77 research outputs found
Generalized Supergravity Equations and Generalized Fradkin-Tseytlin Counterterm
The generalized Fradkin-Tseytlin counterterm for the (type I) Green-Schwarz
superstring is determined for background fields satisfying the generalized
supergravity equations (GSE). For this purpose, we revisit the derivation of
the GSE based upon the requirement of kappa-symmetry of the superstring action.
Lifting the constraint of vanishing bosonic torsion components, we are able to
make contact to several different torsion constraints used in the literature.
It is argued that a natural geometric interpretation of the GSE vector field
that generalizes the dilaton is as the torsion vector, which can combine with
the dilatino spinor into the torsion supervector. To find the counterterm, we
use old results for the one-loop effective action of the heterotic sigma model.
The counterterm is covariant and involves the worldsheet torsion for vanishing
curvature, but cannot be constructed as a local functional in terms of the
worldsheet metric. It is shown that the Weyl anomaly cancels without imposing
any further constraints on the background fields. In the case of ordinary
supergravity, it reduces to the Fradkin-Tseytlin counterterm modulo an
additional constraint.Comment: 23 pages, v2: added reference and extended discussion of the
counterter
On the number of soft quanta in classical field configurations
A crucial ingredient in the large-N quantum portrait of black holes proposed
by Dvali and Gomez is the estimate of the number of soft quanta that make up
the classical gravitational field. It is argued here that the coherent state
formalism provides a way to calculate that number directly. As a consequence,
the average energy of the soft quanta is such that the typical geometric size
of the field source can be roughly interpreted as their de Broglie wavelength.
The calculation is done for the electromagnetic field and for Newtonian
gravity, and it is argued that the number of soft quanta should be unchanged in
General Relativity due to the long range nature of gravity.Comment: 5 pages, v.2: small text changes and added reference
Quantum Portrait of a Black Hole with P\"oschl-Teller Potential
We improve upon the simple model studied by Casadio and Orlandi [JHEP 1308
(2013) 025] for a black hole as a condensate of gravitons. Instead of the
harmonic oscillator potential, the P\"oschl-Teller potential is used, which
allows for a continuum of scattering states. The quantum mechanical model is
embedded into a relativistic wave equation for a complex Klein-Gordon field,
and the charge of the field is interpreted as the gravitational charge (mass)
carried by the graviton condensate.Comment: 12 pages, 1 figure, v2: typos correcte
An improved correspondence formula for AdS/CFT with multi-trace operators
An improved correspondence formula is proposed for the calculation of
correlation functions of a conformal field theory perturbed by multi-trace
operators from the analysis of the dynamics of the dual field theory in Anti-de
Sitter space. The formula reduces to the usual AdS/CFT correspondence formula
in the case of single-trace perturbations.Comment: 6 pages, v.2: minor corrections, v.3: version to appear in PL
Exact 1/N expansion of Wilson loop correlators in Super-Yang-Mills theory
Supersymmetric circular Wilson loops in Super-Yang-Mills
theory are discussed starting from their Gaussian matrix model representations.
Previous results on the generating functions of Wilson loops are reviewed and
extended to the more general case of two different loop contours, which is
necessary to discuss coincident loops with opposite orientations. A
combinatorial formula representing the connected correlators of multiply wound
Wilson loops in terms of the matrix model solution is derived. Two new results
are obtained on the expectation value of the circular Wilson loop, the
expansion of which into a series in and to all orders in the 't~Hooft
coupling was derived by Drukker and Gross about twenty years ago. The
connected correlators of two multiply wound Wilson loops with arbitrary winding
numbers are calculated as a series in . The coefficient functions are
derived not only as power series in , but also to all orders in
by expressing them in terms of the coefficients of the Drukker and
Gross series. This provides an efficient way to calculate the series,
which can probably be generalized to higher-point correlators.Comment: 45 pages, 3 tables, v2: typos corrected and reference updat
Reparameterization Dependence and Holographic Complexity of Black Holes
We refine the calculation of holographic complexity of black holes in the
complexity equals action approach by applying the recently introduced criterion
that the action of any causal diamond in static vacuum regions must vanish
identically. This criterion fixes empty anti-de Sitter (AdS) spacetime as the
reference state with vanishing complexity and renders holographic complexity
explicitly finite in all the cases we consider. The cases considered here
include the Reissner-Nordstr\"om-AdS black hole, the rotating BTZ black hole,
the Kerr-AdS black hole, and AdS-Vaidya spacetime. The criterion is equivalent
to imposing that the corner contributions vanish. Contrary to earlier results,
we find that the generalized Lloyd bound always holds in the
Reissner-Nordstr\"om-AdS and BTZ cases.Comment: 41 pages, 9 figures, v2: added references, v3: part on AdS-Kerr
totally rewritte
Conformal Primary Basis for Dirac Spinors
We study solutions to the Dirac equation in Minkowski space
that transform as -dimensional conformal primary
spinors under the Lorentz group . Such solutions are parameterized
by a point in and a conformal dimension . The set of
wavefunctions that belong to the principal continuous series, , with and in the massive
and massless cases, respectively, form a complete basis of delta-function
normalizable solutions of the Dirac equation. In the massless case, the
conformal primary wavefunctions are related to the wavefunctions in momentum
space by a Mellin transform.Comment: 21 pages, v2: added references, v3: added calculation of the explicit
form of the wave functio
Reparameterization Dependence is Useful for Holographic Complexity
Holographic complexity in the "complexity equals action" approach is
reconsidered relaxing the requirement of reparameterization invariance of the
action with the prescription that the action vanish in any vacuum causal
diamond. This implies that vacuum anti-de Sitter space plays the role of the
reference state. Moreover, the complexity of an anti-de Sitter-Schwarzschild
black hole becomes intrinsically finite and saturates Lloyd's bound after a
critical time. It is also argued that several artifacts, such as the unphysical
negative-time interval, can be removed by truly considering the bulk dual of
the thermofield double state.Comment: 33 pages, 7 figures, v2: references added, v3: added section on BTZ
black hole, version to appear in JHE
Effective Fluid Description of the Dark Universe
We propose an effective anisotropic fluid description for a generic
infrared-modified theory of gravity. In our framework, the additional component
of the acceleration, commonly attributed to dark matter, is explained as a
radial pressure generated by the reaction of the dark energy fluid to the
presence of baryonic matter. Using quite general assumptions, and a microscopic
description of the fluid in terms of a Bose-Einstein condensate of gravitons,
we find the static, spherically symmetric solution for the metric in terms of
the Misner-Sharp mass function and the fluid pressure. At galactic scales, we
correctly reproduce the leading MOND-like and subleading
terms in the weak-field expansion of the potential. Our
description also predicts a tiny (of order for a typical spiral
galaxy) Machian modification of the Newtonian potential at galactic scales,
which is controlled by the cosmological acceleration.Comment: 13 pages, no figures. Replaced version: major revisions in the
introduction, microscopic derivation of Tully-Fisher relation using
Bose-Einstein condensate of gravitons. Some typos correcte
Very Special Relativity in Curved Space-Times
The generalization of Cohen and Glashow's Very Special Relativity to curved
space-times is considered. Gauging the SIM(2) symmetry does not, in general,
provide the coupling to the gravitational background. However, locally SIM(2)
invariant Lagrangians can always be constructed. For space-times with SIM(2)
holonomy, they describe chiral fermions propagating freely as massive
particles.Comment: 7 page
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