94 research outputs found
Viscosity bound for anisotropic superfluids in higher derivative gravity
In the present paper, based on the principles of gauge/gravity duality we
analytically compute the shear viscosity to entropy ratio corresponding to the
superfluid phase in Einstein Gauss-Bonnet gravity. From our analysis we note
that the ratio indeed receives a finite temperature correction below certain
critical temperature. This proves the non universality of shear viscosity to
entropy ratio in higher derivative theories of gravity. We also compute the
upper bound for the Gauss-Bonnet coupling corresponding to the symmetry broken
phase and note that the upper bound on the coupling does not seem to change as
long as we are close to the critical point of the phase diagram. However the
corresponding lower bound of the shear viscosity to entropy ratio seems to get
modified due to the finite temperature effects.Comment: 27 pages; v2: Details added, typos fixed, references updated; version
to appear in JHE
Probing analytical and numerical integrability: The curious case of
Motivated by recent studies related to integrability of string motion in
various backgrounds via analytical and numerical procedures, we discuss these
procedures for a well known integrable string background . We start by revisiting conclusions from earlier studies on string
motion in and and then move on
to more complex problems of and
. Discussing both analytically and numerically, we deduce that
while strings do not encounter any irregular trajectories,
string motion in the deformed five-sphere can indeed, quite surprisingly, run
into chaotic trajectories. We discuss the implications of these results both on
the procedures used and the background itself.Comment: 31 pages, 3 figures, references updated, analysis for Spiky strings
in section (4.1) have been revised, version to appear in JHE
Entanglement entropy from surface terms in general relativity
Entanglement entropy in local quantum field theories is typically ultraviolet
divergent due to short distance effects in the neighbourhood of the entangling
region. In the context of gauge/gravity duality, we show that surface terms in
general relativity are able to capture this entanglement entropy. In
particular, we demonstrate that for 1+1 dimensional CFTs at finite temperature
whose gravity dual is the BTZ black hole, the Gibbons-Hawking-York term
precisely reproduces the entanglement entropy which can be computed
independently in the field theory.Comment: 6 pages 1 fig. Essay awarded honourable mention in the Gravity
Research Foundation 2013 Awards for Essays on Gravitation. v2: to appear in
IJMPD spl. issu
Entanglement entropy in higher derivative holography
We consider holographic entanglement entropy in higher derivative gravity
theories. Recently Lewkowycz and Maldacena arXiv:1304.4926 have provided a
method to derive the equations for the entangling surface from first
principles. We use this method to compute the entangling surface in four
derivative gravity. Certain interesting differences compared to the two
derivative case are pointed out. For Gauss-Bonnet gravity, we show that in the
regime where this method is applicable, the resulting equations coincide with
proposals in the literature as well as with what follows from considerations of
the stress tensor on the entangling surface. Finally we demonstrate that the
area functional in Gauss-Bonnet holography arises as a counterterm needed to
make the Euclidean action free of power law divergences.Comment: 24 pages, 1 figure. v3: typos corrected, published versio
Circuit complexity in interacting QFTs and RG flows
We consider circuit complexity in certain interacting scalar quantum field
theories, mainly focusing on the theory. We work out the circuit
complexity for evolving from a nearly Gaussian unentangled reference state to
the entangled ground state of the theory. Our approach uses Nielsen's geometric
method, which translates into working out the geodesic equation arising from a
certain cost functional. We present a general method, making use of integral
transforms, to do the required lattice sums analytically and give explicit
expressions for the cases. Our method enables a study of circuit
complexity in the epsilon expansion for the Wilson-Fisher fixed point. We find
that with increasing dimensionality the circuit depth increases in the presence
of the interaction eventually causing the perturbative calculation to
breakdown. We discuss how circuit complexity relates with the renormalization
group.Comment: 50 pages, 2 figures; references updated; version to appear in JHE
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