353 research outputs found
Continuous Hawking-Page transitions in Einstein-scalar gravity
We investigate continuous Hawking-Page transitions in Einstein's gravity
coupled to a scalar field with an arbitrary potential in the weak gravity
limit. We show that this is only possible in a singular limit where the
black-hole horizon marginally traps a curvature singularity. Depending on the
subleading terms in the potential, a rich variety of continuous phase
transitions arise. Our examples include second and higher order, including the
Berezinskii-Kosterlitz-Thouless type. In the case when the scalar is dilaton,
the condition for a continuous phase transition lead to (asymptotically)
linear-dilaton background. We obtain the scaling laws of thermodynamic
functions, as well as the viscosity coefficients near the transition. In the
limit of weak gravitational interactions, the bulk viscosity asymptotes to a
universal constant, independent of the details of the scalar potential. As a
byproduct of our analysis we obtain a one-parameter family of kink solutions in
arbitrary dimension d that interpolate between AdS near the boundary and
linear-dilaton background in the deep interior. The continuous Hawking-Page
transitions found here serve as holographic models for normal-to superfluid
transitions.Comment: 35 pages + appendice
Holographic bulk viscosity: GPR vs EO
Recently Eling and Oz (EO) proposed a formula for the holographic bulk
viscosity, in arXiv:1103.1657, derived from the null horizon focusing equation.
This formula seems different from that obtained earlier by Gubser, Pufu and
Rocha (GPR) in arXiv:0806.0407 calculated from the IR limit of the two-point
function of the trace of the stress tensor. The two were shown to agree only
for some simple scaling cases. We point out that the two formulae agree in two
non-trivial holographic theories describing RG flows. The first is the strongly
coupled N=2* gauge theory plasma. The second is the semi-phenomenological model
of Improved Holographic QCD.Comment: 21 pages, 2 figure
The holographic quantum effective potential at finite temperature and density
We develop a formalism that allows the computation of the quantum effective
potential of a scalar order parameter in a class of holographic theories at
finite temperature and charge density. The effective potential is a valuable
tool for studying the ground state of the theory, symmetry breaking patterns
and phase transitions. We derive general formulae for the effective potential
and apply them to determine the phase transition temperature and density in the
scaling region.Comment: 27 page
Instability and Degeneracy in the BMN Correspondence
Non-degenerate perturbation theory, which was used to calculate the scale
dimension of operators on the gauge theory side of the correspondence, breaks
down when effects of triple trace operators are included. We interpret this as
an instability of excited single-string states in the dual string theory for
decay into the continuum of degenerate 3-string states. We apply time-dependent
perturbation theory to calculate the decay widths from gauge theory. These
widths are new gauge theory data which can be compared with future calculations
in light cone string field theory.Comment: 23 pages, no figure
Non-Riemannian gravity actions from double field theory
Non-Riemannian gravitational theories suggest alternative avenues to
understand properties of quantum gravity and provide a concrete setting to
study condensed matter systems with non-relativistic symmetry. Derivation of an
action principle for these theories generally proved challenging for various
reasons. In this technical note, we employ the formulation of double field
theory to construct actions for a variety of such theories. This formulation
helps removing ambiguities in the corresponding equations of motion. In
particular, we embed Torsional Newton-Cartan gravity, Carrollian gravity and
String Newton-Cartan gravity in double field theory, derive their actions and
compare with the previously obtained results in literature
Predictions for PP-wave string amplitudes from perturbative SYM
The role of general two-impurity multi-trace operators in the BMN
correspondence is explored. Surprisingly, the anomalous dimensions of all
two-impurity multi-trace BMN operators to order g_2^2\lambda' are completely
determined in terms of single-trace anomalous dimensions. This is due to
suppression of connected field theory diagrams in the BMN limit and this fact
has important implications for some string theory processes on the PP-wave
background. We also make gauge theory predictions for the matrix elements of
the light-cone string field theory Hamiltonian in the two string-two string and
one string-three string sectors.Comment: 46 pages, 12 figures. V3:typos correcte
On the Temperature Dependence of the Shear Viscosity and Holography
We examine the structure of the shear viscosity to entropy density ratio
eta/s in holographic theories of gravity coupled to a scalar field, in the
presence of higher derivative corrections. Thanks to a non-trivial scalar field
profile, eta/s in this setup generically runs as a function of temperature. In
particular, its temperature behavior is dictated by the shape of the scalar
potential and of the scalar couplings to the higher derivative terms. We
consider a number of dilatonic setups, but focus mostly on phenomenological
models that are QCD-like. We determine the geometric conditions needed to
identify local and global minima for eta/s as a function of temperature, which
translate to restrictions on the signs and ranges of the higher derivative
couplings. Finally, such restrictions lead to an holographic argument for the
existence of a global minimum for eta/s in these models, at or above the
deconfinement transition.Comment: references adde
Holographic Conformal Window - A Bottom Up Approach
We propose a five-dimensional framework for modeling the background geometry
associated to ordinary Yang-Mills (YM) as well as to nonsupersymmetric gauge
theories possessing an infrared fixed point with fermions in various
representations of the underlying gauge group. The model is based on the
improved holographic approach, on the string theory side, and on the
conjectured all-orders beta function for the gauge theory one. We first analyze
the YM gauge theory. We then investigate the effects of adding flavors and show
that, in the holographic description of the conformal window, the geometry
becomes AdS when approaching the ultraviolet and the infrared regimes. As the
number of flavors increases within the conformal window we observe that the
geometry becomes more and more of AdS type over the entire energy range.Comment: 20 Pages, 3 Figures. v2: references adde
Robustness of Sound Speed and Jet Quenching for Gauge/Gravity Models of Hot QCD
We probe the effectiveness and robustness of a simple gauge/gravity dual
model of the QCD fireball that breaks conformal symmetry by constructing a
family of similar geometries that solve the scalar/gravity equations of motion.
This family has two parameters, one of which is associated to the temperature.
We calculate two quantities, the speed of sound and the jet-quenching
parameter. We find the speed of sound to be universal and robust over all the
geometries when appropriate units are used, while the jet-quenching parameter
varies significantly away from the conformal limit. We note that the overall
structure of the jet-quenching depends strongly on whether the running scalar
is the dilaton or not. We also discuss the variation of the scalar potential
over our family of solutions, and truncate our results to where the associated
error is small.Comment: 21 pages, 9 figures, LaTeX. v2:references added, minor correction to
speed of sound; conclusions unchange
Holographic models for undoped Weyl semimetals
We continue our recently proposed holographic description of single-particle
correlation functions for four-dimensional chiral fermions with Lifshitz
scaling at zero chemical potential, paying particular attention to the
dynamical exponent z = 2. We present new results for the spectral densities and
dispersion relations at non-zero momenta and temperature. In contrast to the
relativistic case with z = 1, we find the existence of a quantum phase
transition from a non-Fermi liquid into a Fermi liquid in which two Fermi
surfaces spontaneously form, even at zero chemical potential. Our findings show
that the boundary system behaves like an undoped Weyl semimetal.Comment: 64 pages, 19 figure
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