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	Immirzi parameter - Wikipedia, the free encyclopedia
		The Immirzi parameter (also known as the Barbero-Immirzi parameter) is a numerical coefficient appearing in loop quantum gravity, a nonperturbative theory of quantum gravity.
		The Immirzi parameter measures the size of the quantum of area in Planck units.
		The Immirzi parameter appears in the denominator because the entropy counts the number of edges puncturing the event horizon, and the Immirzi parameter is proportional to the area contributed by each puncture.
	en.wikipedia.org /wiki/Immirzi_parameter (606 words)

	Loop quantum gravity (Site not responding. Last check: 2007-10-08)
		While string/M-theory does not need the Immirzi parameter, it can as yet only derive the Hawking formula for extremal fl holes and near-extremal fl holes -- fl holes with a net electric charge, which differ from the nearly neutral fl holes formed from the collapse of electrically neutral matter such as neutron stars.
		Modulo the Immirzi parameter, which is the only free parameter of LQG, it matches it on average, and additionally predicts a fine structure to it, which is experimentally testable and potentially an improvement.
		The Immirzi discrepancy was believed to be proportional to the logarithm of two or three, and a speculative explanation in terms of quasinormal modes was proposed.
	loop-quantum-gravity.iqnaut.net (6515 words)

	CiteULike: Quantum Gravity, Torsion, Parity Violation and all that (Site not responding. Last check: 2007-10-08)
		In particular, we study the coupling of fermionic degrees of freedom in the presence of torsion and the physical meaning of the Immirzi parameter from the viewpoint of effective field theory.
		We derive the low-energy effective lagrangian which turns out to involve two parameters, one measuring the non-minimal coupling of fermions in the presence of torsion, the other being the Immirzi parameter.
		On the other hand, purely imaginary values of the Immirzi parameter lead to violations of unitarity for the case of non-minimal coupling.
	www.citeulike.org /user/jrw/article/326462 (420 words)

	Quantum Gravity Students
		Constraints in a three dimensional space (corresponding to parameters for hadrons, leptons and massless particles) show that current observational data is consistent with the quantum gravity model.
		The allowed parameter space is strongly constrained in the positive region where the particles would be able to move propagate at speeds faster than light, and the sign ambiguity for the hadronic parameter is removed altogether.
		It is shown that the statistical mechanics of the model reduces to that of a simple non-interacting gas of distinguishable particles with spin.
	academics.hamilton.edu /physics/smajor/students.html (968 words)

	Roh-Suan Tung: the Origin of the Immirzi Parameter
		Chung-Hsien Chou, Roh-Suan Tung, Hoi-Lai Yu "Using quadratic spinor techniques we demonstrate that the Immirzi parameter can be expressed as ratio between scalar and pseudo-scalar contributions in the theory and can be interpreted as a measure of how Einstein gravity differs from a generally constructed covariant theory for gravity.
		One of the important advantage of deriving the Immirzi parameter using the quadratic spinor techniques is to allow the introduction of renormalization scale associated with the Immirzi parameter through the expectation value of the spinor field upon quantization."
		[7] A. Perez and C. Rovelli, “Physical effects of the Immirzi parameter”, http://arxiv.org/gr-qc/0505081.
	www.physicsforums.com /showthread.php?t=88051 (656 words)

	Wikinfo \| Loop quantum gravity (Site not responding. Last check: 2007-10-08)
		While String/M-theory does not need the Immirzi parameter, it can only derive the correct Hawking formula for extremal fl holes -- fl holes with a net electric charge, which are unlikely to exist physically.
		To date, the Immirzi cannot be derived from more fundamental principles, and is an unavoidable artifact of quantization of general relativity's field equations.
		After Baez announced in his column This Week's Finds that Olaf Dreyer had found a connection between the Immirzi Parameter and the asymptotic behaviour of fl hole quasinormal modes (in numerical general relativity), Lubos Motl wasted no time proving that the exact asymptotic behaviour was as predicted numerically.
	wikinfo.org /wiki.php?title=Loop_quantum_gravity (3571 words)

	The Immirzi parameter
		We don't yet know how to derive this parameter from first principles, so we are free to set it to whatever we want to get this fl hole entropy calculation to work.
		The cool part is, Dreyer's calculation of the Immirzi parameter gives the same answer as the SO(3) loop quantum gravity calculation if the exact number is: ln(3) / 8 pi = 0.043712394070757472250...
		If the numbers really match, we'll have two completely different calculations that both give the same formula for the Immirzi parameter, and thus the fundamental quantum of area: a calculation using loop quantum gravity, and a semiclassical calculation a la Bohr based on the properties of vibrating fl holes.
	www.lns.cornell.edu /spr/2002-11/msg0046358.html (565 words)

	Re: The Immirzi parameter
		Let me explain the actual situation, not just for you, but for everyone else who may be wondering what this "Immirzi parameter" business is all about.
		But before I stop, I should note that when people read Immirzi's paper, they got very excited and started calling beta the "Immirzi parameter", much to the annoyance of poor old Fernando Barbero, who had discovered it.
		People also got sick of having this parameter be negative, so they defined gamma = -beta and worked with positive values of gamma.
	www.lns.cornell.edu /spr/2001-06/msg0033558.html (1017 words)

	RRI Digital Repository: Item 2289/1188 (Site not responding. Last check: 2007-10-08)
		The Immirzi parameter is a free parameter which appears in the physical predictions of loop quantum gravity and is sometimes viewed as a quantization ambiguity.
		Interpretations have been offered for the Immirzi ambiguity, but there does not appear to be a clear understanding or even a consensus about its origin and significance.
		We show that a previously discussed example containing a “finite dimensional analogue” of the Immirzi ambiguity is fallacious, in the sense that the ambiguity in this example is not intrinsic to the system, but introduced artificially by compactifying the configuration space.
	dspace.rri.res.in:8080 /dspace/handle/2289/1188 (124 words)

	Spin networks, spin foams and loop quantum gravity
		The Immirzi parameter in quantum general relativity, 1997.
		Immirzi Ambiguity, Boosts and Conformal Frames for Black Holes, 2003.
		Shows that in the presence of fermions, the Immirzi parameter appears in the equations of motion.
	jdc.math.uwo.ca /spin-foams (2360 words)

	BF \| Musings
		and this is indeed pretty small as long as the immirzi parameter is not tuned to be one.
		The main emphasis is put on the immirzi parameter which is not a theta term and still induces gravitational cp violation.
		In particular, the Immirzi parameter of the Euclidean theory is pure-imaginary (i.e.
	golem.ph.utexas.edu /~distler/blog/archives/000541.html (6970 words)

	The Reference Frame: Quasinormal story on quasinormal modes
		In this case, there are "metastable" modes in which the particle sits in the "hole" for quite a long time, but eventually it escapes by quantum tunneling (the rate of the tunneling exponentially depends on the parameters, which is why the lifetime of various alpha-decays are so incredibly diverse in size).
		This is not a random value of mass (or frequency): numerically, it was found to be the asymptotic real part of the highly-damped quasinormal frequencies of a neutral fl hole.
		The singular point would have been unknowable and a none-fixed boundary, except for the fact that it simply exhibits very simple parameters that is easily measurable from outside, i.e., the total mass, total angular momentum, and total charge, the "three hairs" of a flhole.
	motls.blogspot.com /2005/03/quasinormal-story-on-quasinormal-modes.html (4214 words)

	Immirzi parameter biography .ms (via CobWeb/3.1 planetlab1.tamu.edu) (Site not responding. Last check: 2007-10-08)
		In 1997, Ashtekar, Baez, Corichi and Krasnov quantized the classical phase space of the exterior of a fl hole in vacuum General Relativity.
		Their result involves the logarithm of a transcendental number instead of the logatithms of integers mentioned above.
		Quantum Geometry of Isolated Horizons and Black Hole Entropy, a calculation incorporating matter and the theory of isolated horizons from General Relativity.
	www.biography.ms.cob-web.org:8888 /Immirzi_parameter.html (553 words)

	RedTram News Search Engine \| News on Physics everywhere (Site not responding. Last check: 2007-10-08)
		A Note on Parity Violation and the Immirzi Parameter.
		There has been considerable recent interest in the Immirzi parameter as a measure of parity violating effects in the classical theory of gravitation with fermion coupling.
		Most recently it was shown that the Immirzi parameter together with the non-minimal coupling
	www.redtram.com /catalogue/world/physics/20051010/2 (887 words)

	Strings and Quantum Gravity
		19] because the asymptotic form of quasi-normal frequencies was shown to be related to the Barbero-Immirzi parameter [
		The imaginary part is large making the numerical analysis cumbersome, but is easy to understand by noting that the spacing of the frequencies
		Thus, its validity is limited to small values of the parameter
	aesop.phys.utk.edu /research/node6.html (530 words)

	Citebase - Immirzi parameter in the Barrett-Crane model?
		Authors: Livine, Richard E. We study the generalised constrained BF theory described in gr-qc/0102073 in order to introduce the Immirzi parameter in spin foam models.
		We show that the resulting spin foam model is still based on simple representations and that the generalised BF action is simply a deformation of the Barrett-Crane model.
		The Immirzi parameter doesn't change the representations used in the spin foam model, so it doesn't affect the geometry of the model.
	citebase.eprints.org /cgi-bin/citations?id=oai:arXiv.org:gr-qc/0103081 (151 words)

	7.3 Entropy
		An added bonus comes from the fact that the isolated horizon framework naturally incorporates not only fl hole horizons but also the cosmological ones for which thermodynamical considerations are also known to apply [99].
		In this case, all the (gravitational, electro-magnetic, and scalar field) multipoles are required as macroscopic parameters to fix the system of interest.
		Therefore, now the appropriate ensemble is determined by fixing all these multipoles to lie in a small range around given values.
	www.emis.ams.org /journals/LRG/Articles/lrr-2004-10/articlesu17.html (983 words)

	Not Even Wrong » Blog Archive » LQG for Skeptics
		One reason for this is of course that most of the parameters in such classes of such theories are irrelevant in the RG sense, and do not influence large scale predictions.
		I agree that to define a theory you have first to define a regulated theory and then study the limit as the regulator is removed and show that the expressions for observables that result have the symmetries and gauge invariances of the classical theory.
		I agree it would be very interesting to know how the parameters of the finite spin foam models map to the parameters of the effective field theory with the appropriate ground state symmetry.
	www.math.columbia.edu /~woit/wordpress/?p=330 (18166 words)

	Spin network - Wikipedia, the free encyclopedia
		According to this formula, the lowest possible non-zero eigenvalue of the area operator corresponds to a link that carries spin 1/2 representation.
		Assuming Immirzi parameter on the order of 1, this gives the smallest possible measurable area of ~10
		The formula for area eigenvalues becomes somewhat more complicated if the surface is allowed to pass through the nodes (it is not yet clear if these situations are physically meaningful.
	en.wikipedia.org /wiki/Spin_network (746 words)

	week112
		So: it seems we can't determine the constant of proportionality in the entropy-area relation, because of this arbitrariness in the Immirzi parameter.
		All we can say is this: we have a theory of the microstates of a fl hole, which predicts that entropy is proportional to area for largish fl holes, and which taken together with the Bekenstein-Hawking calculation allows us to determine the Immirzi parameter.
		Under certain assumptions on the Hamiltonian we find that, although the emission spectrum consists of distinct lines, the curve enveloping the spectrum is close to the Planck thermal distribution with temperature given by the thermodynamical temperature of the fl hole as defined by the derivative of the entropy with respect to the fl hole mass.
	math.ucr.edu /home/baez/week112.html (3437 words)

	The Reference Frame: Objections to loop quantum gravity
		Indeed, the infinitely many parameters that govern the effective action and make quantized general relativity non-renormalizable and unpredictive are simply replaced by an infinite number of parameters of the Hamiltonian constraint and/or the spin foam Feynman rules.
		While string theory confirms general relativity or its extensions at long distances - where GR is tested - and modifies it at the shorter ones, loop quantum gravity does just the opposite.
		The only non-trivial check could be the coefficient, but it comes out incorrectly (see the Immirzi discrepancy).
	motls.blogspot.com /2004/10/objections-to-loop-quantum-gravity.html (5350 words)

	Luboš Motl's reference frame: March 2005 (Site not responding. Last check: 2007-10-08)
		Jacques considered generic cubic superpotentials of "N" chiral superfields that are constrained to preserve a "Z_4" R-symmetry under which the fields are odd, and therefore the superpotential must be an odd function.
		It is straightforward but tedious to calculate the average values of the superpotential, the squared potential (second moment), as well as all other conceivable polynomials of the roots (vacua) - sums over all roots (vacua); all the average values are polynomials in the variables "a,b" themselves.
		You essentially know how to do it if you know that the coefficients in a quadratic equation are the sum and the product of the roots, respectively, and similar rules apply for higher degree polynomials, even if they are polynomials of many variables.
	www.physics.harvard.edu /~motl/2005_03_01_motls_archive.html (14120 words)

	The LQG Landscape \| Musings
		This paper seems to indicate that the Immirzi parameter cannot be set arbitrarily once fermions are included.
		The original hope was that the Immirzi term would yield parity violating effects via torsion in the effective field theory.
		However, the Immirzi parameter is taken to be something completely different, to adjust the fl hole entropy etc.
	golem.ph.utexas.edu /~distler/blog/archives/000855.html (12660 words)

	Luboš Motl's reference frame: August 2005 (Site not responding. Last check: 2007-10-08)
		There is shockingly one more paper about the Immirzi parameter: a new value of it is proposed.
		Although many people would be happy if someone else referred to their (my) work often, I am personally very confused what all these guys want to do and why they think it's interesting; see the quasinormal story on quasinormal modes.
		For example, a crackpot may think that it is important for the neutron lifetime to be something like 885.2 seconds, and the main task is to develop calculations that lead to this "magic" number.
	www.physics.harvard.edu /~motl/2005_08_01_motls_archive.html (12731 words)

	Astro-ph for busy people (Site not responding. Last check: 2007-10-08)
		With the unusually complex velocity structure resolved in the NV profiles, this system is unlikely to represent a traditional galaxy disk/corona.
		The redshift of an L^* galaxy (z=0.9289), at an impact parameter of 38h^-1 kpc is consistent with the redshift of this system.
		I show that, for different angular momenta of the compact object, the valid disk parameter region dramatically changes and disk may become unstable in certain situations.
	www.camk.edu.pl /~gwar/astro-ph/2003.03.06.html (6990 words)

	Meissner corrects the Immirzi parameter
		Hence, the value of the Barbero-Immirzi parameter involved in the spectra of all the geometric and physical operators in this theory is different than previously derived."
		There was a time when Lubos Motl and friends would argue that LQG must be wrong because of some small numerical difference in Immirzi gotten by calculating this way and that.
		Unfortunately it was found that the part of the spectra of the types of quasinormal modes conjectured to fix the immirzi-barbero parameter depends on the kind of hole we're talking about.
	www.physicsforums.com /showthread.php?p=257709 (2041 words)

	Quantization of area: the plot thickens
		Given this, it was tempting to attribute the entropy of a fl hole to microstates of its event horizon, and to describe these in terms of spin network edges puncturing the horizon.
		On the one hand this is good: it's a way to determine the Barbero-Immirzi parameter, and thus the quantum of area, which works out to
		This makes for a pretty picture in which almost all the spin network edges puncturing the event horizon carry one quantum of area and one qubit of information, as in Wheeler's `it from bit' scenario [9].
	www.phys.lsu.edu /mog/mog21/node11.html (1421 words)

	Holostars: Black Holes Without Event Horizons - an Astronomy Net Blackholes2 Forum Message
		A large charged/rotating holostar can be regarded as the classical analogue of a quantum gravity spin-network state.
		If the links of a large spin network state are identified with the interior relativistic particles of the holostar solution, the Immirzi parameter can be determined.
		Its value is roughly a factor of 4.8 higher than the result derived by Ashtekar et.al.
	www.astronomy.net /forums/blackholes2/messages/4846.shtml (963 words)

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