<?xml version="1.0" encoding="ISO-8859-1"?><article xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<front>
<journal-meta>
<journal-id>0035-001X</journal-id>
<journal-title><![CDATA[Revista mexicana de física]]></journal-title>
<abbrev-journal-title><![CDATA[Rev. mex. fis.]]></abbrev-journal-title>
<issn>0035-001X</issn>
<publisher>
<publisher-name><![CDATA[Sociedad Mexicana de Física]]></publisher-name>
</publisher>
</journal-meta>
<article-meta>
<article-id>S0035-001X2011000500003</article-id>
<title-group>
<article-title xml:lang="en"><![CDATA[Oriented matroid theory and loop quantum gravity in (2+2) and eight dimensions]]></article-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J.A.]]></given-names>
</name>
<xref ref-type="aff" rid="A01"/>
</contrib>
</contrib-group>
<aff id="A01">
<institution><![CDATA[,Arizona State University  ]]></institution>
<addr-line><![CDATA[Tempe AZ]]></addr-line>
<country>USA</country>
</aff>
<pub-date pub-type="pub">
<day>11</day>
<month>10</month>
<year>2011</year>
</pub-date>
<pub-date pub-type="epub">
<day>11</day>
<month>10</month>
<year>2011</year>
</pub-date>
<volume>57</volume>
<numero>5</numero>
<fpage>400</fpage>
<lpage>405</lpage>
<copyright-statement/>
<copyright-year/>
<self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_arttext&amp;pid=S0035-001X2011000500003&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_abstract&amp;pid=S0035-001X2011000500003&amp;lng=en&amp;nrm=iso"></self-uri><self-uri xlink:href="http://www.scielo.org.mx/scielo.php?script=sci_pdf&amp;pid=S0035-001X2011000500003&amp;lng=en&amp;nrm=iso"></self-uri><abstract abstract-type="short" xml:lang="en"><p><![CDATA[We establish a connection between oriented matroid theory and loop quantum gravity in (2+2) (two time and two space dimensions) and 8-dimensions. We start by observing that supersymmetry implies that the structure constants of the real numbers, complex numbers, quaternions and octonions can be identified with the chirotope concept. This means, among other things, that normed divisions algebras, which are only possible in 1,2, 4 or 8-dimensions, are linked to oriented matroid theory. Therefore, we argue that the possibility for developing loop quantum gravity in 8-dimensions must be taken as important alternative. Moreover, we show that in 4-dimensions, loop quantum gravity theories in the (1+3) or (0+4) signatures are not the only possibilities. In fact, we show that loop quantum gravity associated with the (2+2)-signature may also be an interesting physical structure.]]></p></abstract>
<kwd-group>
<kwd lng="en"><![CDATA[Loop quantum gravity]]></kwd>
<kwd lng="en"><![CDATA[eight dimensions]]></kwd>
<kwd lng="en"><![CDATA[(2+2)-dimensions]]></kwd>
</kwd-group>
</article-meta>
</front><body><![CDATA[  	    <p align="justify"><font face="verdana" size="4">Investigaci&oacute;n</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="center"><font face="verdana" size="4"><b>Oriented matroid theory and loop quantum gravity in (2+2) and eight dimensions</b></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="center"><font face="verdana" size="2"><b>J.A. Nieto</b></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><i>Mathematical, Computational &amp; Modeling Science Center, Arizona State University, PO Box 871904, Tempe, AZ 85287, USA. Facultad de Ciencias F&iacute;sico&#45;Matem&aacute;ticas de la Universidad Aut&oacute;noma de Sinaloa, 80010, Culiac&aacute;n Sinaloa, M&eacute;xico. Departamento de Investigaci&oacute;n en F&iacute;sica de la Universidad de Sonora, 83000, Hermosillo Sonora, M&eacute;xico.</i></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2">Recibido el 18 de noviembre de 2010;    ]]></body>
<body><![CDATA[<br> 	aceptado el 26 de julio de 2011</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Abstract</b></font></p>  	    <p align="justify"><font face="verdana" size="2">We establish a connection between oriented matroid theory and loop quantum gravity in (2+2) (two time and two space dimensions) and 8&#45;dimensions. We start by observing that supersymmetry implies that the structure constants of the real numbers, complex numbers, quaternions and octonions can be identified with the chirotope concept. This means, among other things, that normed divisions algebras, which are only possible in 1,2, 4 or 8&#45;dimensions, are linked to oriented matroid theory. Therefore, we argue that the possibility for developing loop quantum gravity in 8&#45;dimensions must be taken as important alternative. Moreover, we show that in 4&#45;dimensions, loop quantum gravity theories in the (1+3) or (0+4) signatures are not the only possibilities. In fact, we show that loop quantum gravity associated with the (2+2)&#45;signature may also be an interesting physical structure.</font></p>  	    <p align="justify"><font face="verdana" size="2"><b>Keywords</b>: Loop quantum gravity; eight dimensions; (2+2)&#45;dimensions.</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2">PACS: 04.60.&#45;m; 04.65.+e; 11.15.&#45;q; 11.30.Ly</font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    <p align="justify"><font face="verdana" size="2"><a href="/pdf/rmf/v57n5/v57n5a3.pdf" target="_blank">DESCARGAR ART&Iacute;CULO EN FORMATO PDF</a></font></p>  	    <p align="justify"><font face="verdana" size="2">&nbsp;</font></p>  	    ]]></body>
<body><![CDATA[<p align="justify"><font face="verdana" size="2"><b>Referencias</b></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">1. A. Ashtekar and J. Lewandowski, <i>Class. Quant. Grav.</i> <b>21</b> (2004) R53; gr&#45;qc/0404018.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371404&pid=S0035-001X201100050000300001&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">2. T. Jacobson and L. Smolin, <i>Class. Quant. Grav.</i> <b>5</b> (1988) 583.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371406&pid=S0035-001X201100050000300002&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">3. J. Samuel, <i>Pramana J. Phys.</i> <b>28</b> (1987) L429.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371408&pid=S0035-001X201100050000300003&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">4. J. A. Nieto, <i>Class. Quant. Grav.</i> <b>22</b> (2005) 947; e&#45;Print: hep&#45;th/0410260.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371410&pid=S0035-001X201100050000300004&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">5. J. A. Nieto, <i>Class. Quant. Grav.</i> <b>23</b> (2006) 4387; e&#45;Print: hep&#45;th/0509169.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371412&pid=S0035-001X201100050000300005&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">6. J. A. Nieto, <i>Gen. Rel. Grav.</i> <b>39</b> (2007) 1109.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371414&pid=S0035-001X201100050000300006&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">7. J. A. Nieto, <i>"Towards a background independent quantum gravity in eight dimensions";</i> e&#45;Print: arXiv:0704.2769.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371416&pid=S0035-001X201100050000300007&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">8. A.R. Dundarer, F. Gursey and C.H. Tze, <i>J. Math. Phys.</i> <b>25</b> (1984) 1496.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371418&pid=S0035-001X201100050000300008&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">9. A. R. Dundarer and F. Gursey, <i>J. Math. Phys.</i> <b>32</b> (1991) 1178.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371420&pid=S0035-001X201100050000300009&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">10. E. Corrigan, C. Devchand, D.B. Fairlie and J. Nuyts, <i>Nucl. Phys.B</i> <b>214</b> (1983)452.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371422&pid=S0035-001X201100050000300010&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">11. H. Nishino and S. Rajpoot, JHEP <b>0404</b> (2004) 020; hep&#45;th/0210132.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371424&pid=S0035-001X201100050000300011&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">12. H. Nishino and S. Rajpoot, <i>Phys. Lett. B</i><b>564</b> (2003) 269; hep&#45;th/0302059.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371426&pid=S0035-001X201100050000300012&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">13. J. C. Baez, <i>Bull. Amer. Math. Soc.</i> <b>39</b> (2002) 145.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371428&pid=S0035-001X201100050000300013&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">14. R. Bott and J. Milnor, <i>Bull. Amer. Math. Soc.</i> <b>64</b> (1958) 87.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371430&pid=S0035-001X201100050000300014&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">15. M. Kervair, <i>Proc. Nat. Acad. Sci.</i> <b>44</b> (1958) 286.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371432&pid=S0035-001X201100050000300015&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">16. S. Okubo, <i>"Introduction to Octonions and Other Non&#45;Associative Alebras in Physics",</i> (Cambridge University Press, 1995).    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371434&pid=S0035-001X201100050000300016&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">17. I. L. Kantor and A. S. Solodovnikov, <i>"Hypercomplex Numbers; An Elementary Introduction to Algebras"</i> (Springer&#45;Verlag, NY, 1989).    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371436&pid=S0035-001X201100050000300017&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">18. J. A. Nieto and L. N. Alejo&#45;Armenta, <i>Int. J. Mod. Phys. A</i> <b>16</b> (2001) 4207; hep&#45;th/0005184.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371438&pid=S0035-001X201100050000300018&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">19. J. A. Wolf, <i>J. Diff. Geom.</i> <b>6</b> (1972) 317;    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371440&pid=S0035-001X201100050000300019&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --><!-- ref --> <i>J. Diff. Geom.</i> <b>7</b> (1972) 19.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371441&pid=S0035-001X201100050000300020&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">20. T. Kugo and P. Townsend, <i>Nucl. Phys. B</i><b>221</b> (1983) 357.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371443&pid=S0035-001X201100050000300021&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">21. D. Grumiller, W. Kummer, and D.V. Vassilevich, <i>Phys. Rept.</i> <b>369</b> (2002) 327, hep&#45;th/0204253.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371445&pid=S0035-001X201100050000300022&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">22. J. A. Nieto, <i>Nuovo Cim. B</i> <b>120</b> (2005) 135; e&#45;Print: hep&#45;th/0410003.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371447&pid=S0035-001X201100050000300023&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">23. C. Hull, <i>JHEP</i> <b>9811</b> (1998) 017;    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371449&pid=S0035-001X201100050000300024&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --> e&#45;Print: hep&#45;th/9807127.</font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">24. M. P. Blencowe and M. J. Duff, <i>Nucl. Phys. B</i><b>310</b> (1988) 387.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371451&pid=S0035-001X201100050000300025&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">25. E. Witten, <i>Phys. Rev. D</i> <b>44</b> (1991) 314.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371453&pid=S0035-001X201100050000300026&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">26. I. Bars, <i>Class. Quant. Grav.</i> <b>18</b> (2001) 3113; e&#45;Print: hep&#45;th/0008164.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371455&pid=S0035-001X201100050000300027&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">27. S. Hwang, <i>Nucl. Phys. B</i><b>354</b> (1991) 100.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371457&pid=S0035-001X201100050000300028&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">28. P.A. Griffin and O. F. Hernandez, <i>Nucl. Phys. B</i><b>356</b> (1991) 287.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371459&pid=S0035-001X201100050000300029&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">29. J. M. Evans, <i>Nucl. Phys. B</i><b>298</b> (1988) 92.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371461&pid=S0035-001X201100050000300030&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">30. A. Bjorner, M. Las Vergnas, B. Sturmfels, N. White and G. M. Ziegler, <i>Oriented Martroids,</i> (Cambridge University Press,Cambridge, 1993).    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371463&pid=S0035-001X201100050000300031&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">31. J. A. Nieto, <i>Rev. Mex. Fis. E</i> <b>51</b> (2005) 5; e&#45;Print: hep&#45;th/0407093.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371465&pid=S0035-001X201100050000300032&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">32. J. A. Nieto, <i>"Maximal supersymmetry in eleven&#45;dimensional supergravity revisited and chirotopes";</i> e&#45;Print: hep&#45;th/0603139.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371467&pid=S0035-001X201100050000300033&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">33. T. Thiemann, <i>"Introduction to modern canonical quantum general relativity",</i> gr&#45;qc/0110034.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371469&pid=S0035-001X201100050000300034&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">34. D. Joyce, <i>J. Diff. Geom.</i> <b>53</b> (1999) 89; math.dg/9910002.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371471&pid=S0035-001X201100050000300035&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">35. R. Gambini and J. Pullin, <i>"Loops, Knots, Gauge Theories and Quantum Gravity"</i> (Cambridge Monographis in Mathematical Physics, 1996).    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371473&pid=S0035-001X201100050000300036&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">36. D. Mulsch and B. Geyer, <i>Int. J. Geom. Meth. Mod. Phys.</i> <b>1</b> (2004) 185; hep&#45;th/0310237.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371475&pid=S0035-001X201100050000300037&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">37. L. Smolin, "An <i>Invitation to loop quantum gravity',</i> published in *Cincinnati 2003, Quantum theory and symmetries* 655682; hep&#45;th/0408048.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371477&pid=S0035-001X201100050000300038&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">38. A. Corichi, <i>J. Phys. Conf. Ser.</i> <b>24</b> (2005) 1; gr&#45;qc/0507038.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371479&pid=S0035-001X201100050000300039&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">39. C. Rovelli, <i>Phys. Rev. D</i> <b>59</b> (1999) 104015; e&#45;Print: gr&#45;qc/9806121.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371481&pid=S0035-001X201100050000300040&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">40. L. Smolin, <i>Nucl. Phys. B</i><b>739</b> (2006) 169; hep&#45;th/0503140.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371483&pid=S0035-001X201100050000300041&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">41. T. Thiemann, <i>Class. Quant. Grav.</i> <b>23</b> 1923 (2006); hep&#45;th/0401172.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371485&pid=S0035-001X201100050000300042&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">42. J. Brunnemann and D. Rideout, <i>Oriented Matroids &#45; Combinatorial Structures Underlying Loop Quantum Gravity,</i> e&#45;Print: arXiv:1003.2348.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371487&pid=S0035-001X201100050000300043&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">43. J. A. Nieto, <i>Adv. Theor. Math. Phys.</i> <b>8</b> (2004) 177; hep&#45;th/0310071.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371489&pid=S0035-001X201100050000300044&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">44. J. A. Nieto, <i>Adv. Theor. Math. Phys.</i> <b>10</b> (2006) 747, hep&#45;th/0506106.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371491&pid=S0035-001X201100050000300045&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">45. J. A. Nieto, <i>J. Math. Phys.</i> <b>45</b> (2004) 285; hep&#45;th/0212100.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371493&pid=S0035-001X201100050000300046&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">46. J. A. Nieto and M. C. Mar&iacute;n, <i>J. Math. Phys.</i> <b>41</b> (2000) 7997.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371495&pid=S0035-001X201100050000300047&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">47. J. A. Nieto and M.C. Mar&iacute;n, <i>Int. J. Mod. Phys. A</i> <b>18</b> (2003) 5261;hep&#45;th/0302193.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371497&pid=S0035-001X201100050000300048&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">48. A. Bachem and W. Kern, <i>Linear Programming Duality; An Introduction of Oriented Matroids</i> (Spring&#45;Verlag Berlin Heidelberg, 1992).    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371499&pid=S0035-001X201100050000300049&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">49. J. A. Nieto, <i>Phys. Lett. A</i> <b>262</b> (1999) 274; e&#45;Print: hep&#45;th/9910049.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371501&pid=S0035-001X201100050000300050&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    ]]></body>
<body><![CDATA[<!-- ref --><p align="justify"><font face="verdana" size="2">50. P. R. Brady, S. Droz, W. Israel and S.M. Morsink, <i>Class. Quant. Grav.</i> <b>13</b> (1996) 2211; e&#45;Print: gr&#45;qc/9510040.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371503&pid=S0035-001X201100050000300051&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">51. R. Geroch, A. Held and R. Penrose, <i>J. Math. Phys.</i> <b>14</b> (1973) 874.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371505&pid=S0035-001X201100050000300052&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">52. M. J. Duff, <i>Phys. Lett. B</i> <b>641</b> (2006) 335;    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371507&pid=S0035-001X201100050000300053&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --> e&#45;Print: hep&#45;th/0602160.</font></p>  	    <!-- ref --><p align="justify"><font face="verdana" size="2">53. H. Ooguri and C. Vafa, <i>Nucl. Phys. B</i><b>361</b> (1991) 469.    &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;[&#160;<a href="javascript:void(0);" onclick="javascript: window.open('/scielo.php?script=sci_nlinks&ref=8371509&pid=S0035-001X201100050000300054&lng=','','width=640,height=500,resizable=yes,scrollbars=1,menubar=yes,');">Links</a>&#160;]<!-- end-ref --></font></p>      ]]></body><back>
<ref-list>
<ref id="B1">
<label>1</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Ashtekar]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Lewandowski]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year>2004</year>
<volume>21</volume>
<page-range>R53</page-range></nlm-citation>
</ref>
<ref id="B2">
<label>2</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Jacobson]]></surname>
<given-names><![CDATA[T.]]></given-names>
</name>
<name>
<surname><![CDATA[Smolin]]></surname>
<given-names><![CDATA[L.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year>1988</year>
<volume>5</volume>
<page-range>583</page-range></nlm-citation>
</ref>
<ref id="B3">
<label>3</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Samuel]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Pramana J. Phys.]]></source>
<year>1987</year>
<volume>28</volume>
<page-range>L429</page-range></nlm-citation>
</ref>
<ref id="B4">
<label>4</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year>2005</year>
<volume>22</volume>
<page-range>947</page-range></nlm-citation>
</ref>
<ref id="B5">
<label>5</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year>2006</year>
<volume>23</volume>
<page-range>4387</page-range></nlm-citation>
</ref>
<ref id="B6">
<label>6</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[A. Nieto]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Gen. Rel. Grav.]]></source>
<year>2007</year>
<volume>39</volume>
<page-range>1109</page-range></nlm-citation>
</ref>
<ref id="B7">
<label>7</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Towards a background independent quantum gravity in eight dimensions]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B8">
<label>8</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Dundarer]]></surname>
<given-names><![CDATA[A.R.]]></given-names>
</name>
<name>
<surname><![CDATA[Gursey]]></surname>
<given-names><![CDATA[F.]]></given-names>
</name>
<name>
<surname><![CDATA[Tze]]></surname>
<given-names><![CDATA[C.H.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Math. Phys.]]></source>
<year>1984</year>
<volume>25</volume>
<page-range>1496</page-range></nlm-citation>
</ref>
<ref id="B9">
<label>9</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Dundarer]]></surname>
<given-names><![CDATA[A. R.]]></given-names>
</name>
<name>
<surname><![CDATA[Gursey]]></surname>
<given-names><![CDATA[F.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Math. Phys.]]></source>
<year>1991</year>
<volume>32</volume>
<page-range>1178</page-range></nlm-citation>
</ref>
<ref id="B10">
<label>10</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Corrigan]]></surname>
<given-names><![CDATA[E.]]></given-names>
</name>
<name>
<surname><![CDATA[Devchand]]></surname>
<given-names><![CDATA[C.]]></given-names>
</name>
<name>
<surname><![CDATA[Fairlie]]></surname>
<given-names><![CDATA[D.B.]]></given-names>
</name>
<name>
<surname><![CDATA[Nuyts]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.B]]></source>
<year>1983</year>
<volume>214</volume>
<page-range>452</page-range></nlm-citation>
</ref>
<ref id="B11">
<label>11</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nishino]]></surname>
<given-names><![CDATA[H.]]></given-names>
</name>
<name>
<surname><![CDATA[Rajpoot]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
</person-group>
<source><![CDATA[JHEP]]></source>
<year></year>
<volume>0404</volume>
<numero>2004</numero>
<issue>2004</issue>
<page-range>020</page-range></nlm-citation>
</ref>
<ref id="B12">
<label>12</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nishino]]></surname>
<given-names><![CDATA[H.]]></given-names>
</name>
<name>
<surname><![CDATA[Rajpoot]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
</person-group>
<source><![CDATA[Phys. Lett.]]></source>
<year>2003</year>
<volume>B564</volume>
<page-range>269</page-range></nlm-citation>
</ref>
<ref id="B13">
<label>13</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Baez]]></surname>
<given-names><![CDATA[J. C.]]></given-names>
</name>
</person-group>
<source><![CDATA[Bull. Amer. Math. Soc.]]></source>
<year>2002</year>
<volume>39</volume>
<page-range>145</page-range></nlm-citation>
</ref>
<ref id="B14">
<label>14</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Bott]]></surname>
<given-names><![CDATA[R.]]></given-names>
</name>
<name>
<surname><![CDATA[Milnor]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Bull. Amer. Math. Soc.]]></source>
<year>1958</year>
<volume>64</volume>
<page-range>87</page-range></nlm-citation>
</ref>
<ref id="B15">
<label>15</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Kervair]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
</person-group>
<source><![CDATA[Proc. Nat. Acad. Sci.]]></source>
<year>1958</year>
<volume>44</volume>
<page-range>286</page-range></nlm-citation>
</ref>
<ref id="B16">
<label>16</label><nlm-citation citation-type="book">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Okubo]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
</person-group>
<source><![CDATA[Introduction to Octonions and Other Non-Associative Alebras in Physics]]></source>
<year>1995</year>
<publisher-loc><![CDATA[Cambridge ]]></publisher-loc>
<publisher-name><![CDATA[University Press]]></publisher-name>
</nlm-citation>
</ref>
<ref id="B17">
<label>17</label><nlm-citation citation-type="book">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Kantor]]></surname>
<given-names><![CDATA[I. L.]]></given-names>
</name>
<name>
<surname><![CDATA[Solodovnikov]]></surname>
<given-names><![CDATA[A. S.]]></given-names>
</name>
</person-group>
<source><![CDATA[Hypercomplex Numbers; An Elementary Introduction to Algebras]]></source>
<year>1989</year>
<publisher-loc><![CDATA[NY ]]></publisher-loc>
<publisher-name><![CDATA[Springer-Verlag]]></publisher-name>
</nlm-citation>
</ref>
<ref id="B18">
<label>18</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
<name>
<surname><![CDATA[Alejo-Armenta]]></surname>
<given-names><![CDATA[L. N.]]></given-names>
</name>
</person-group>
<source><![CDATA[Int. J. Mod. Phys.]]></source>
<year>2001</year>
<volume>A 16</volume>
<page-range>4207</page-range></nlm-citation>
</ref>
<ref id="B19">
<label>19</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Wolf]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Diff. Geom.]]></source>
<year>1972</year>
<volume>6</volume>
<page-range>317</page-range></nlm-citation>
</ref>
<ref id="B20">
<nlm-citation citation-type="journal">
<source><![CDATA[J. Diff. Geom.]]></source>
<year>1972</year>
<volume>7</volume>
<page-range>19</page-range></nlm-citation>
</ref>
<ref id="B21">
<label>20</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Kugo]]></surname>
<given-names><![CDATA[T.]]></given-names>
</name>
<name>
<surname><![CDATA[Townsend]]></surname>
<given-names><![CDATA[P.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>1983</year>
<volume>B221</volume>
<page-range>357</page-range></nlm-citation>
</ref>
<ref id="B22">
<label>21</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Grumiller]]></surname>
<given-names><![CDATA[D.]]></given-names>
</name>
<name>
<surname><![CDATA[Kummer]]></surname>
<given-names><![CDATA[W.]]></given-names>
</name>
<name>
<surname><![CDATA[Vassilevich]]></surname>
<given-names><![CDATA[D.V.]]></given-names>
</name>
</person-group>
<source><![CDATA[Phys. Rept.]]></source>
<year>2002</year>
<volume>369</volume>
<page-range>327</page-range></nlm-citation>
</ref>
<ref id="B23">
<label>22</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nuovo Cim.]]></source>
<year>2005</year>
<volume>B 120</volume>
<page-range>135</page-range><page-range>e-Print: hep-th/0410003</page-range></nlm-citation>
</ref>
<ref id="B24">
<label>23</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Hull]]></surname>
<given-names><![CDATA[C.]]></given-names>
</name>
</person-group>
<source><![CDATA[JHEP]]></source>
<year></year>
<volume>9811</volume>
<numero>1998</numero>
<issue>1998</issue>
<page-range>017</page-range></nlm-citation>
</ref>
<ref id="B25">
<label>24</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Blencowe]]></surname>
<given-names><![CDATA[M. P.]]></given-names>
</name>
<name>
<surname><![CDATA[Duff]]></surname>
<given-names><![CDATA[M. J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>1988</year>
<volume>B310</volume>
<page-range>387</page-range></nlm-citation>
</ref>
<ref id="B26">
<label>25</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Witten]]></surname>
<given-names><![CDATA[E.]]></given-names>
</name>
</person-group>
<source><![CDATA[Phys. Rev. D]]></source>
<year>1991</year>
<volume>44</volume>
<page-range>314</page-range></nlm-citation>
</ref>
<ref id="B27">
<label>26</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Bars]]></surname>
<given-names><![CDATA[I.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year></year>
<volume>18</volume>
<numero>2001</numero>
<issue>2001</issue>
<page-range>3113</page-range></nlm-citation>
</ref>
<ref id="B28">
<label>27</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Hwang]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>1991</year>
<volume>B354</volume>
<page-range>100</page-range></nlm-citation>
</ref>
<ref id="B29">
<label>28</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Griffin]]></surname>
<given-names><![CDATA[P.A.]]></given-names>
</name>
<name>
<surname><![CDATA[Hernandez]]></surname>
<given-names><![CDATA[O. F.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>1991</year>
<volume>B356</volume>
<page-range>287</page-range></nlm-citation>
</ref>
<ref id="B30">
<label>29</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Evans]]></surname>
<given-names><![CDATA[J. M.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>1988</year>
<volume>B298</volume>
<page-range>92</page-range></nlm-citation>
</ref>
<ref id="B31">
<label>30</label><nlm-citation citation-type="book">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Bjorner]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Las Vergnas]]></surname>
<given-names><![CDATA[M.]]></given-names>
</name>
<name>
<surname><![CDATA[Sturmfels]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
<name>
<surname><![CDATA[White]]></surname>
<given-names><![CDATA[N.]]></given-names>
</name>
<name>
<surname><![CDATA[Ziegler]]></surname>
<given-names><![CDATA[G. M.]]></given-names>
</name>
</person-group>
<source><![CDATA[Oriented Martroids]]></source>
<year>1993</year>
<publisher-loc><![CDATA[Cambridge ]]></publisher-loc>
<publisher-name><![CDATA[Cambridge University Press]]></publisher-name>
</nlm-citation>
</ref>
<ref id="B32">
<label>31</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Rev. Mex. Fis. E]]></source>
<year>2005</year>
<volume>51</volume>
<page-range>5</page-range></nlm-citation>
</ref>
<ref id="B33">
<label>32</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Maximal supersymmetry in eleven-dimensional supergravity revisited and chirotopes]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B34">
<label>33</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Thiemann]]></surname>
<given-names><![CDATA[T.]]></given-names>
</name>
</person-group>
<source><![CDATA[Introduction to modern canonical quantum general relativity]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B35">
<label>34</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Joyce]]></surname>
<given-names><![CDATA[D.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Diff. Geom.]]></source>
<year>1999</year>
<volume>53</volume>
<page-range>89</page-range></nlm-citation>
</ref>
<ref id="B36">
<label>35</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Gambini]]></surname>
<given-names><![CDATA[R.]]></given-names>
</name>
<name>
<surname><![CDATA[Pullin]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Loops, Knots, Gauge Theories and Quantum Gravity]]></source>
<year>1996</year>
</nlm-citation>
</ref>
<ref id="B37">
<label>36</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Mulsch]]></surname>
<given-names><![CDATA[D.]]></given-names>
</name>
<name>
<surname><![CDATA[Geyer]]></surname>
<given-names><![CDATA[B.]]></given-names>
</name>
</person-group>
<source><![CDATA[Int. J. Geom. Meth. Mod. Phys.]]></source>
<year>2004</year>
<volume>1</volume>
<page-range>185</page-range></nlm-citation>
</ref>
<ref id="B38">
<label>37</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Smolin]]></surname>
<given-names><![CDATA[L.]]></given-names>
</name>
</person-group>
<article-title xml:lang="en"><![CDATA[An Invitation to loop quantum gravity]]></article-title>
<source><![CDATA[Cincinnati 2003, Quantum theory and symmetries]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B39">
<label>38</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Corichi]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Phys. Conf. Ser.]]></source>
<year></year>
<volume>24</volume>
<numero>2005</numero>
<issue>2005</issue>
<page-range>1</page-range></nlm-citation>
</ref>
<ref id="B40">
<label>39</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Rovelli]]></surname>
<given-names><![CDATA[C.]]></given-names>
</name>
</person-group>
<source><![CDATA[Phys. Rev.]]></source>
<year></year>
<volume>D 59</volume>
<numero>1999</numero>
<issue>1999</issue>
<page-range>104015</page-range></nlm-citation>
</ref>
<ref id="B41">
<label>40</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Smolin]]></surname>
<given-names><![CDATA[L.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>2006</year>
<volume>B739</volume>
<page-range>169</page-range><page-range>hep-th/0503140</page-range></nlm-citation>
</ref>
<ref id="B42">
<label>41</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Thiemann]]></surname>
<given-names><![CDATA[T.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year>2006</year>
<volume>23</volume>
<numero>1923</numero>
<issue>1923</issue>
</nlm-citation>
</ref>
<ref id="B43">
<label>42</label><nlm-citation citation-type="">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Brunnemann]]></surname>
<given-names><![CDATA[J.]]></given-names>
</name>
<name>
<surname><![CDATA[Rideout]]></surname>
<given-names><![CDATA[D.]]></given-names>
</name>
</person-group>
<source><![CDATA[Oriented Matroids - Combinatorial Structures Underlying Loop Quantum Gravity]]></source>
<year></year>
</nlm-citation>
</ref>
<ref id="B44">
<label>43</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Adv. Theor. Math. Phys.]]></source>
<year>2004</year>
<volume>8</volume>
<page-range>177</page-range></nlm-citation>
</ref>
<ref id="B45">
<label>44</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A]]></given-names>
</name>
</person-group>
<source><![CDATA[Adv. Theor. Math. Phys.]]></source>
<year>2006</year>
<volume>10</volume>
<page-range>747</page-range></nlm-citation>
</ref>
<ref id="B46">
<label>45</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Math. Phys.]]></source>
<year>2004</year>
<volume>45</volume>
<page-range>285</page-range></nlm-citation>
</ref>
<ref id="B47">
<label>46</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
<name>
<surname><![CDATA[Marín]]></surname>
<given-names><![CDATA[M. C.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Math. Phys.]]></source>
<year>2000</year>
<volume>41</volume>
<page-range>7997</page-range></nlm-citation>
</ref>
<ref id="B48">
<label>47</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
<name>
<surname><![CDATA[Marín]]></surname>
<given-names><![CDATA[M.C.]]></given-names>
</name>
</person-group>
<source><![CDATA[Int. J. Mod. Phys.]]></source>
<year>2003</year>
<volume>A 18</volume>
<page-range>5261</page-range></nlm-citation>
</ref>
<ref id="B49">
<label>48</label><nlm-citation citation-type="book">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Bachem]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Kern]]></surname>
<given-names><![CDATA[W.]]></given-names>
</name>
</person-group>
<source><![CDATA[Linear Programming Duality; An Introduction of Oriented Matroids]]></source>
<year>1992</year>
<publisher-name><![CDATA[Spring-Verlag Berlin Heidelberg]]></publisher-name>
</nlm-citation>
</ref>
<ref id="B50">
<label>49</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Nieto]]></surname>
<given-names><![CDATA[J. A.]]></given-names>
</name>
</person-group>
<source><![CDATA[Phys. Lett.]]></source>
<year>1999</year>
<volume>A 262</volume>
<page-range>274</page-range></nlm-citation>
</ref>
<ref id="B51">
<label>50</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Brady]]></surname>
<given-names><![CDATA[P. R.]]></given-names>
</name>
<name>
<surname><![CDATA[Droz]]></surname>
<given-names><![CDATA[S.]]></given-names>
</name>
<name>
<surname><![CDATA[Israel]]></surname>
<given-names><![CDATA[W.]]></given-names>
</name>
<name>
<surname><![CDATA[Morsink]]></surname>
<given-names><![CDATA[S.M.]]></given-names>
</name>
</person-group>
<source><![CDATA[Class. Quant. Grav.]]></source>
<year>1996</year>
<volume>13</volume>
<page-range>2211</page-range></nlm-citation>
</ref>
<ref id="B52">
<label>51</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Geroch]]></surname>
<given-names><![CDATA[R.]]></given-names>
</name>
<name>
<surname><![CDATA[Held]]></surname>
<given-names><![CDATA[A.]]></given-names>
</name>
<name>
<surname><![CDATA[Penrose]]></surname>
<given-names><![CDATA[R.]]></given-names>
</name>
</person-group>
<source><![CDATA[J. Math. Phys.]]></source>
<year>1973</year>
<volume>14</volume>
<page-range>874</page-range></nlm-citation>
</ref>
<ref id="B53">
<label>52</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Duff]]></surname>
<given-names><![CDATA[M. J.]]></given-names>
</name>
</person-group>
<source><![CDATA[Phys. Lett.]]></source>
<year>2006</year>
<volume>B 641</volume>
<page-range>335</page-range></nlm-citation>
</ref>
<ref id="B54">
<label>53</label><nlm-citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname><![CDATA[Ooguri]]></surname>
<given-names><![CDATA[H.]]></given-names>
</name>
<name>
<surname><![CDATA[Vafa]]></surname>
<given-names><![CDATA[C.]]></given-names>
</name>
</person-group>
<source><![CDATA[Nucl. Phys.]]></source>
<year>1991</year>
<volume>B361</volume>
<page-range>469</page-range></nlm-citation>
</ref>
</ref-list>
</back>
</article>
