3,760 research outputs found
Holst Actions for Supergravity Theories
Holst action containing Immirzi parameter for pure gravity is generalised to
the supergravity theories. Supergravity equations of motion are not modified by
such generalisations, thus preserving supersymmetry. Dependence on the Immirzi
parameter does not emerge in the classical equations of motion. This is in
contrast with the recent observation of Perez and Rovelli for gravity action
containing original Holst term and a minimally coupled Dirac fermion where the
classical equations of motion do develop a dependence on Immirzi parameter.Comment: 15 page
Spin nematic ground state of the triangular lattice S=1 biquadratic model
Motivated by the spate of recent experimental and theoretical interest in
Mott insulating S=1 triangular lattice magnets, we consider a model S=1
Hamiltonian on a triangular lattice interacting with rotationally symmetric
biquadratic interactions. We show that the partition function of this model can
be expressed in terms of configurations of three colors of tightly-packed,
closed loops with {\em non-negative} weights, which allows for efficient
quantum Monte Carlo sampling on large lattices. We find the ground state has
spin nematic order, i.e. it spontaneously breaks spin rotation symmetry but
preserves time reversal symmetry. We present accurate results for the
parameters of the low energy field theory, as well as finite-temperature
thermodynamic functions
Logarithmic correction to the Bekenstein-Hawking entropy of the BTZ black hole
We derive an exact expression for the partition function of the Euclidean BTZ
black hole. Using this, we show that for a black hole with large horizon area,
the correction to the Bekenstein-Hawking entropy is , in
agreement with that for the Schwarzschild black hole obtained in the canonical
gravity formalism and also in a Lorentzian computation of BTZ black hole
entropy. We find that the right expression for the logarithmic correction in
the context of the BTZ black hole comes from the modular invariance associated
with the toral boundary of the black hole.Comment: LaTeX, 10 pages, typos corrected, clarifications adde
Strongly Inhomogeneous Phases and Non-Fermi Liquid Behavior in Randomly Depleted Kondo Lattices
We investigate the low-temperature behavior of Kondo lattices upon random
depletion of the local -moments, by using strong-coupling arguments and
solving SU() saddle-point equations on large lattices. For a large range of
intermediate doping levels, between the coherent Fermi liquid of the dense
lattice and the single-impurity Fermi liquid of the dilute limit, we find
strongly inhomogeneous states that exhibit distinct non-Fermi liquid
characteristics. In particular, the interplay of dopant disorder and strong
interactions leads to rare weakly screened moments which dominate the bulk
susceptibility. Our results are relevant to compounds like Ce_{x}La_{1-x}CoIn_5
and Ce_{x}La_{1-x}Pb_3Comment: 4 pages, 5 figure
A Continuous Injection Plasma Model for the X-Ray/Radio Knots in Kpc-Scale Jets of AGN
We consider the evolution of a spherically expanding plasma cloud, where
there is continuous injection of non-thermal electrons. We compute the time
dependent electron distribution and resultant photon spectra taking into
account synchrotron, adiabatic and inverse Compton cooling. This model is
different from previous works where, instead of a continuous injection of
particles, a short injection period was assumed. We apply this model to the
radio/optical knots in the large scale jets of AGN, detected in X-rays by {\it
Chandra} and find that the overall broadband spectral features can be
reproduced. It is shown that for some sources, constraints on the X-ray
spectral index (by a longer {\it Chandra} observation) will be able to
differentiate between the different models. This in turn will put a strong
constraint on the acceleration mechanism active in these sources.Comment: Accepted for publications in the Astrophysical Journal Letter
Black Hole Entropy from a Highly Excited Elementary String
Suggested correspondence between a black hole and a highly excited elementary
string is explored. Black hole entropy is calculated by computing the density
of states for an open excited string. We identify the square root of oscillator
number of the excited string with Rindler energy of black hole to obtain an
entropy formula which, not only agrees at the leading order with the
Bekenstein-Hawking entropy, but also reproduces the logarithmic correction
obtained for black hole entropy in the quantum geometry framework. This
provides an additional supporting evidence for correspondence between black
holes and strings.Comment: revtex, 4 page
Schwarzschild horizon dynamics and SU(2) Chern-Simons theory
We discuss the effect of different choices in partial gauge fixing of bulk
local Lorentz invariance, on the description of the horizon degrees of freedom
of a Schwarzschild black hole as an SU(2) Chern-Simons theory with specific
sources. A classically equivalent description in terms of an ISO(2)
Chern-Simons theory is also discussed. Further, we demonstrate that both these
descriptions can be partially gauge fixed to a horizon theory with U(1) local
gauge invariance, with the solder form sources being subject to extra
constraints in directions orthogonal to an internal vector field left invariant
by U(1) transformations. Seemingly disparate approaches on characterization of
the horizon theory for the Schwarzschild black hole (as well as spherical
Isolated Horizons in general) are thus shown to be equivalent physically.Comment: 22 pages Latex, no figures, version accepted for publication in
Physical Review
Quantum criticality of U(1) gauge theories with fermionic and bosonic matter in two spatial dimensions
We consider relativistic U(1) gauge theories in 2+1 dimensions, with N_b
species of complex bosons and N_f species of Dirac fermions at finite
temperature. The quantum phase transition between the Higgs and Coulomb phases
is described by a conformal field theory (CFT). At large N_b and N_f, but for
arbitrary values of the ratio N_b/N_f, we present computations of various
critical exponents and universal amplitudes for these CFTs. We make contact
with the different spin-liquids, charge-liquids and deconfined critical points
of quantum magnets that these field theories describe. We compute physical
observables that may be measured in experiments or numerical simulations of
insulating and doped quantum magnets.Comment: 30 pages, 8 figure
- …