789 research outputs found
Entropy of Killing horizons from Virasoro algebra in D-dimensional extended Gauss-Bonnet gravity
We treat D-dimensional black holes with Killing horizon for extended
Gauss-Bonnet gravity. We use Carlip method and impose boundary conditions on
horizon what enables us to identify Virasoro algebra and evaluate its central
charge and Hamiltonian eigenvalue. The Cardy formula allows then to calculate
the number of states and thus provides for microscopic interpretation of
entropy.Comment: 15 page
Experimental evidence of a fractal dissipative regime in high-T_c superconductors
We report on our experimental evidence of a substantial geometrical
ingredient characterizing the problem of incipient dissipation in high-T_c
superconductors(HTS): high-resolution studies of differential
resistance-current characteristics in absence of magnetic field enabled us to
identify and quantify the fractal dissipative regime inside which the actual
current-carrying medium is an object of fractal geometry. The discovery of a
fractal regime proves the reality and consistency of critical-phenomena
scenario as a model for dissipation in inhomogeneous and disordered HTS, gives
the experimentally-based value of the relevant finite-size scaling exponent and
offers some interesting new guidelines to the problem of pairing mechanisms in
HTS.Comment: 5 pages, 3 figures, RevTex; Accepted for publication in Physical
Review B; (figures enlarged
Axial gravity: a non-perturbative approach to split anomalies
In a theory of a Dirac fermion field coupled to a metric-axial-tensor (MAT)
background, using a Schwinger-DeWitt heat kernel technique, we compute
non-perturbatively the two (odd parity) trace anomalies. A suitable collapsing
limit of this model corresponds to a theory of chiral fermions coupled to
(ordinary) gravity. Taking this limit on the two computed trace anomalies we
verify that they tend to the same expression, which coincides with the already
found odd parity trace anomaly, with the identical coefficient. This confirms
our previous results on this issue.Comment: 43 pages, some additions in section 6.3 and 6.5 plus minor
correction
Axial gravity, massless fermions and trace anomalies
This article deals with two main topics. One is odd parity trace anomalies in
Weyl fermion theories in a 4d curved background, the second is the introduction
of axial gravity. The motivation for reconsidering the former is to clarify the
theoretical background underlying the approach and complete the calculation of
the anomaly. The reference is in particular to the difference between Weyl and
massless Majorana fermions and to the possible contributions from tadpole and
seagull terms in the Feynman diagram approach. A first, basic, result of this
paper is that a more thorough treatment, taking account of such additional
terms { and using dimensional regularization}, confirms the earlier result. The
introduction of an axial symmetric tensor besides the usual gravitational
metric is instrumental to a different derivation of the same result using Dirac
fermions, which are coupled not only to the usual metric but also to the
additional axial tensor. The action of Majorana and Weyl fermions can be
obtained in two different limits of such a general configuration. The results
obtained in this way confirm the previously obtained ones.Comment: 55 pages, comments added in section 2 and 5. Sections 6.4, 6.6, 7,
7.1, 7.2 and Appendices 5.3, 5.5 partially modifie
Perturbative spectrum of the dressed sliver
We analyze the fluctuations of the dressed sliver solution found in a previous paper, hep-th/0311198, in the operator formulation of Vacuum String Field Theory. We derive the tachyon wave function and then analyze the higher level fluctuations. We show that the dressing is responsible for implementing the transversality condition on the massless vector. In order to consistently deal with the singular k = 0 mode we introduce a string midpoint regulator and we show that it is possible to accommodate all the open string states among the solutions to the linearized equations of motion. We finally show how the dressing can give rise to the correct ratio between the energy density of the dressed sliver and the brane tension computed via the three-tachyons-coupling
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