352 research outputs found
Scanning the Parameter Space of Holographic Superconductors
We study various physical quantities associated with holographic s-wave
superconductors as functions of the scaling dimensions of the dual condensates.
A bulk scalar field with negative mass squared , satisfying the
Breitenlohner-Freedman stability bound and the unitarity bound, and allowed to
vary in unit intervals, were considered. We observe that all the physical
quantities investigated are sensitive to the scaling dimensions of the dual
condensates. For all the , the characteristic lengths diverge at the
critical temperature in agreement with the Ginzburg-Landau theory. The
Ginzburg-Landau parameter, obtained from these length scales indicates that the
holographic superconductors can be type I or type II depending on the charge
and the scaling dimensions of the dual condensates. For a fixed charge, there
exists a critical scaling dimension, above which a holographic superconductor
is type I, below which it becomes a type II.Comment: 24 pages 47 figure
The Coherent Crooks Equality
This chapter reviews an information theoretic approach to deriving quantum
fluctuation theorems. When a thermal system is driven from equilibrium, random
quantities of work are required or produced: the Crooks equality is a classical
fluctuation theorem that quantifies the probabilities of these work
fluctuations. The framework summarised here generalises the Crooks equality to
the quantum regime by modeling not only the driven system but also the control
system and energy supply that enables the system to be driven. As is reasonably
common within the information theoretic approach but high unusual for
fluctuation theorems, this framework explicitly accounts for the energy
conservation using only time independent Hamiltonians. We focus on explicating
a key result derived by Johan {\AA}berg: a Crooks-like equality for when the
energy supply is allowed to exist in a superposition of energy eigenstates
states.Comment: 11 pages, 3 figures; Chapter for the book "Thermodynamics in the
Quantum Regime - Recent Progress and Outlook", eds. F. Binder, L. A. Correa,
C. Gogolin, J. Anders and G. Adess
Coarse-Graining Can Beat the Rotating Wave Approximation in Quantum Markovian Master Equations
We present a first-principles derivation of the Markovian semi-group master equation without invoking the rotating wave approximation (RWA). Instead we use a time coarse-graining approach which leaves us with a free timescale parameter, which we can optimize. Comparing this approach to the standard RWA-based Markovian master equation, we find that significantly better agreement is possible using the coarse-graining approach, for a three-level model coupled to a bath of oscillators, whose exact dynamics we can solve for at zero temperature. The model has the important feature that the RWA has a non-trivial effect on the dynamics of the populations. We show that the two different master equations can exhibit strong qualitative differences for the population of the energy eigenstates even for such a simple model. The RWA-based master equation misses an important feature which the coarse-graining based scheme does not. By optimizing the coarse-graining timescale the latter scheme can be made to approach the exact solution much more closely than the RWA-based master equation
AdS/CFT with Flavour in Electric and Magnetic Kalb-Ramond Fields
We investigate gauge/gravity duals with flavour for which pure-gauge
Kalb-Ramond B fields are turned on in the background, into which a D7 brane
probe is embedded. First we consider the case of a magnetic field in two of the
spatial boundary directions. We show that at finite temperature, i.e. in the
AdS-Schwarzschild background, the B field has a stabilizing effect on the
mesons and chiral symmetry breaking occurs for a sufficiently large value of
the B field. Then we turn to the electric case of a B field in the temporal
direction and one spatial boundary direction. In this case, there is a singular
region in which it is necessary to turn on a gauge field on the brane in order
to ensure reality of the brane action. We find that the brane embeddings are
attracted towards this region. Far away from this region, in the weak field
case at zero temperature, we investigate the meson spectrum and find a mass
shift similar to the Stark effect.Comment: 34 pages, 18 figures, v2: added references and comments on mode
decoupling, on thermodynamics and holographic renormalisation, JHEP style,
v3: Final published versio
Holographic Studies of Entanglement Entropy in Superconductors
We present the results of our studies of the entanglement entropy of a
superconducting system described holographically as a fully back-reacted
gravity system, with a stable ground state. We use the holographic prescription
for the entanglement entropy. We uncover the behavior of the entropy across the
superconducting phase transition, showing the reorganization of the degrees of
freedom of the system. We exhibit the behaviour of the entanglement entropy
from the superconducting transition all the way down to the ground state at
T=0. In some cases, we also observe a novel transition in the entanglement
entropy at intermediate temperatures, resulting from the detection of an
additional length scale.Comment: 21 pages, 14 figures. v2:Clarified some remarks concerning stability.
v3: Updated to the version that appears in JHE
Energy Loss of Heavy Quarks from Asymptotically AdS Geometries
We investigate some universal features of AdS/CFT models of heavy quark
energy loss. In addition, as a specific example, we examine quark damping in
the spinning D3-brane solution dual to N=4 SU(N_c) super Yang-Mills at finite
temperature and R-charge chemical potential.Comment: 17 pages, 9 figures; v2 refs added, typo fixe
Holographic Aspects of Fermi Liquids in a Background Magnetic Field
We study the effects of an external magnetic field on the properties of the
quasiparticle spectrum of the class of 2+1 dimensional strongly coupled
theories holographically dual to charged AdS black holes at zero
temperature. We uncover several interesting features. At certain values of the
magnetic field, there are multiple quasiparticle peaks representing a novel
level structure of the associated Fermi surfaces. Furthermore, increasing
magnetic field deforms the dispersion characteristics of the quasiparticle
peaks from non-Landau toward Landau behaviour. At a certain value of the
magnetic field, just at the onset of Landau-like behaviour of the Fermi liquid,
the quasiparticles and Fermi surface disappear.Comment: 18 pages, 10 figures. Revised some of the terminology: changed
non-separable solutions to infinite-sum solution
Criticality, Scaling and Chiral Symmetry Breaking in External Magnetic Field
We consider a D7-brane probe of in the presence of pure
gauge -field. The dual gauge theory is flavored Yang-Mills theory in
external magnetic field. We explore the dependence of the fermionic condensate
on the bare quark mass and study the discrete self-similar behavior of
the theory near the origin of the parametric space. We calculate the critical
exponents of the bare quark mass and the fermionic condensate. A study of the
meson spectrum supports the expectation based on thermodynamic considerations
that at zero bare quark mass the stable phase of the theory is a chiral
symmetry breaking one. Our study reveals the self-similar structure of the
spectrum near the critical phase of the theory, characterized by zero fermionic
condensate and we calculate the corresponding critical exponent of the meson
spectrum.Comment: 29 pages, 9 figures. Accepted in JHEP. Updated to mach the published
version. One figure added, some definitions improve
Dynamics of Fundamental Matter in N=2* Yang-Mills Theory
We study the dynamics of quenched fundamental matter in
supersymmetric large SU(N) Yang-Mills theory at zero temperature. Our tools
for this study are probe D7-branes in the holographically dual
Pilch-Warner gravitational background. Previous work using
D3-brane probes of this geometry has shown that it captures the physics of a
special slice of the Coulomb branch moduli space of the gauge theory, where the
constituent D3-branes form a dense one dimensional locus known as the
enhancon, located deep in the infrared. Our present work shows how this physics
is supplemented by the physics of dynamical flavours, revealed by the D7-branes
embeddings we find. The Pilch-Warner background introduces new divergences into
the D7-branes free energy, which we are able to remove with a single
counterterm. We find a family of D7-brane embeddings in the geometry and
discuss their properties. We study the physics of the quark condensate,
constituent quark mass, and part of the meson spectrum. Notably, there is a
special zero mass embedding that ends on the enhancon, which shows that while
the geometry acts repulsively on the D7-branes, it does not do so in a way that
produces spontaneous chiral symmetry breaking.Comment: 24 pages, 8 figures. Corrected typos, added comment about
counterterm. To appear in JHE
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