88 research outputs found
Dynamical gauge fields and anomalous transport at strong coupling
Anomalous transport coefficients are known to be universal in the absence of
dynamical gauge fields. We calculate the corrections to these universal values
due to dynamical gluon fields at strong coupling, at finite temperature and
finite density, using the holographic duality. We show that the consistent
chiral magnetic and chiral vortical currents receive no corrections, while we
derive a semi-analytic formula for the chiral separation conductivity. We
determine these corrections in the large color, large flavor limit, in terms of
a series expansion in the anomalous dimension of the axial current in
terms of physical parameters , temperature, electric and chiral
chemical potentials and the flavor to color ratio . Our
results are applicable to a generic class of chiral gauge theories that allow
for a holographic description in the gravity approximation. We also determine
the dynamical gluon corrections to the chiral vortical separation current in a
particular example in the absence of external axial fields.Comment: 28 pages + appendices, 3 figure
Strongly-coupled anisotropic gauge theories and holography
We initiate a non-perturbative study of anisotropic, non-conformal and
confining gauge theories that are holographically realized in gravity by
generic Einstein-Axion-Dilaton systems. In the vacuum our solutions describe RG
flows from a conformal field theory in the UV to generic scaling solutions in
the IR with generic hyperscaling violation and dynamical exponents and
. We formulate a generalization of the holographic c-theorem to the
anisotropic case. At finite temperature, we discover that the anisotropic
deformation reduces the confinement-deconfinement phase transition temperature
suggesting a possible alternative explanation of inverse magnetic catalysis
solely based on anisotropy. We also study transport and diffusion properties in
anisotropic theories and observe in particular that the butterfly velocity that
characterizes both diffusion and growth of chaos transverse to the anisotropic
direction, saturates a constant value in the IR which can exceed the bound
given by the conformal value.Comment: 6 pages, 4 figures; v2: minor improvements, references added, version
accepted for publication in PR
Realizations of pseudo bosonic theories with non-diagonal automorphisms
Pseudo conformal field theories are theories with the same fusion rules, but
with different modular matrix as some conventional field theory. One of the
authors defined these and conjectured that, for bosonic systems, they can all
be realized by some actual RCFT, which is of free bosons. We complete the proof
here by treating the non diagonal automorphism case. It is shown that for
characteristics they are all equivalent to a diagonal case, fully
classified in our previous publication. For we realize the non diagonal
case, establishing this theorem.Comment: 12 pages, no figure
Quasi-normal modes of a strongly coupled non-conformal plasma and approach to criticality
We study fluctuations around equilibrium in a class of strongly interacting
non-conformal plasmas using holographic techniques. In particular we calculate
the quasi-normal mode spectrum of black hole backgrounds that approach to
Chamblin-Reall plasmas in the IR. In a specific limit, related to the exact
linear-dilaton background in string theory, we observe that the plasma
approaches criticality and we obtain the quasi-normal spectrum analytically. We
regulate the critical limit by gluing the IR geometry that corresponds to the
non-conformal plasma to a part of AdS space-time in the UV. Near criticality,
we find two sets of quasi-normal modes, related to the IR and UV parts of the
geometry. In the critical limit, the quasi-normal modes accumulate to form a
branch cut in the correlators of the energy-momentum tensor on the real axis of
the complex frequency plane.Comment: 6 pages, 4 figure
On conformal field theories at fractional levels
For each lattice one can define a free boson theory propagating on the
corresponding torus. We give an alternative definition where one employs any
automorphism of the group . This gives a wealth of conformal data, which
we realize as some bosonic theory, in all the `regular' cases. We discuss the
generalization to affine theories. As a byproduct, we compute the gauss sum for
any lattice and any diagonal automorphism
Clinical Supervision Model in Teaching Practice: Does it Make a Difference in Supervisors’ Performance?
In search for better practices there has been a plethora of research in preservice teacher training. To contribute to the literature, the current study aims at investigating teacher trainees’ and cooperating teachers’ views about the performance and contribution of supervisors during teaching practice after using Clinical Supervision Model. Experimental in design, the study gathered both qualitative and quantitative data from participants in the experimental (n= 108 CT; n= 191 TT) and control (n=32 CT; n=100TT) groups. The findings revealed that there are statistically significant differences in participants’ evaluations of their university supervisor in favor of the experimental group, suggesting the implementation of Clinical Supervision Model for teaching practice
Universal rapidity scaling of entanglement entropy inside hadrons from conformal invariance
When a hadron is probed at high energy, a non-trivial quantum entanglement
entropy inside the hadron emerges due to the lack of complete information about
the hadron wave function extracted from this measurement. In the high energy
limit, the hadron becomes a maximally entangled state, with a linear dependence
of entanglement entropy on rapidity, as has been found in a recent analysis
based on parton description. In this Letter, we use an effective conformal
field theoretic description of hadrons on the lightcone to show that the linear
dependence of the entanglement entropy on rapidity found in parton description
is a general consequence of approximate conformal invariance and does not
depend on the assumption of weak coupling. Our result also provides further
evidence for a duality between the parton and string descriptions of hadrons.Comment: 5 pages, 1 figur
Topology change in commuting saddles of thermal N=4 SYM theory
We study the large N saddle points of weakly coupled N=4 super Yang-Mills
theory on S^1 x S^3 that are described by a commuting matrix model for the
seven scalar fields {A_0, \Phi_J}. We show that at temperatures below the
Hagedorn/`deconfinement' transition the joint eigenvalue distribution is S^1 x
S^5. At high temperatures T >> 1/R_{S^3}, the eigenvalues form an ellipsoid
with topology S^6. We show how the deconfinement transition realises the
topology change S^1 x S^5 --> S^6. Furthermore, we find compelling evidence
that when the temperature is increased to T = 1/(\sqrt\lambda R_{S^3}) the
saddle with S^6 topology changes continuously to one with S^5 topology in a new
second order quantum phase transition occurring in these saddles.Comment: 1+40 pages, 6 figures. v2: Title changed. Status of commuting saddles
clarified: New high T phase transition claimed in the commuting sector only,
not in the full theor
Holographic entanglement as nonlocal magnetism
The Ryu-Takayanagi prescription can be cast in terms of a set of microscopic
threads that help visualize holographic entanglement in terms of distillation
of EPR pairs. While this framework has been exploited for regions with a high
degree of symmetry, we take the first steps towards understanding general
entangling regions, focusing on AdS. Inspired by simple constructions
achieved for the case of disks and the half-plane, we reformulate bit threads
in terms of a magnetic-like field generated by a current flowing through the
boundary of the entangling region. The construction is possible for these
highly symmetric settings, leading us to a modified Biot-Savart law in curved
space that fully characterizes the entanglement structure of the state. For
general entangling regions, the prescription breaks down as the corresponding
modular Hamiltonians become inherently nonlocal. We develop a formalism for
general shape deformations and derive a flow equation that accounts for these
effects as a systematic expansion. We solve this equation for a complete set of
small deformations and show that the structure of the expansion explicitly
codifies the expected nonlocalities. Our findings are consistent with numerical
results existing in the literature, and shed light on the fundamental nature of
quantum entanglement as a nonlocal phenomenon.Comment: 28 pages, 5 figure
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
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