96 research outputs found
The Stress-Energy Tensor of Flavor Fields from AdS/CFT
We use the AdS/CFT correspondence to study the transport properties of
massive N=2 hypermultiplet fields in an N=4 SU(Nc) super-Yang-Mills theory
plasma in the large Nc, large 't Hooft coupling limit, and in the presence of a
baryon number chemical potential and external electric and magnetic fields. In
particular, we compute the flavor fields' contribution to the stress-energy
tensor. We find infrared divergences in the stress-energy tensor, arising from
the flavor fields' constant rate of energy and momentum loss. We regulate these
divergences and extract the energy and momentum loss rates from the divergent
terms. We also check our result in various limits in which the divergences are
absent. The supergravity dual is a system of D7-branes, with a particular
configuration of worldvolume fields, probing an AdS-Schwarzschild background.
The supergravity calculation amounts to computing the stress-energy tensor of
the D7-branes.Comment: 32 pages; v2, added one footnote in section 2.2, added one reference,
version published in JHE
Holographic Flavor Transport in Arbitrary Constant Background Fields
We use gauge-gravity duality to compute a new transport coefficient
associated with a number Nf of massive N=2 supersymmetric hypermultiplet fields
propagating through an N=4 SU(Nc) super-Yang-Mills theory plasma in the limits
of large Nc and large 't Hooft coupling, with Nf << Nc. We introduce a baryon
number density as well as arbitrary constant electric and magnetic fields,
generalizing previous calculations by including a magnetic field with a
component parallel to the electric field. We can thus compute all components of
the conductivity tensor associated with transport of baryon number charge,
including a component never before calculated in gauge-gravity duality. We also
compute the contribution that the flavor degrees of freedom make to the
stress-energy tensor, which exhibits divergences associated with the rates of
energy and momentum loss of the flavor degrees of freedom. We discuss two
currents that are free from these divergences, one of which becomes anomalous
when the magnetic field has a component parallel to the electric field and
hence may be related to recent study of charge transport in the presence of
anomalies.Comment: 27 page
Spinning Dragging Strings
We use the AdS/CFT correspondence to compute the drag force experienced by a
heavy quark moving through a maximally supersymmetric SU(N) super Yang-Mills
plasma at nonzero temperature and R-charge chemical potential and at large 't
Hooft coupling. We resolve a discrepancy in the literature between two earlier
studies of such quarks. In addition, we consider small fluctuations of the
spinning strings dual to these probe quarks and find no evidence of
instabilities. We make some comments about suitable D7-brane boundary
conditions for the dual strings.Comment: 25 pages, 4 figures; v2 refs added; v3 to appear in JHEP, clarifying
comment
Holographic Thermodynamics at Finite Baryon Density: Some Exact Results
We use the AdS/CFT correspondence to study the thermodynamics of massive N=2
supersymmetric hypermultiplets coupled to N=4 supersymmetric SU(Nc) Yang-Mills
theory in the limits of large Nc and large 't Hooft coupling. In particular, we
study the theory at finite baryon number density. At zero temperature, we
present an exact expression for the hypermultiplets' leading-order contribution
to the free energy, and in the supergravity description we clarify which
D-brane configuration is appropriate for any given value of the chemical
potential. We find a second-order phase transition when the chemical potential
equals the mass. At finite temperature, we present an exact expression for the
hypermultiplets' leading-order contribution to the free energy at zero mass.Comment: 21 pages, 1 figure; v2 corrected typos, added comments to sections
2.2 and 2.
Critical Exponents from AdS/CFT with Flavor
We use the AdS/CFT correspondence to study the thermodynamics of massive N=2
supersymmetric hypermultiplet flavor fields coupled to N=4 supersymmetric
SU(Nc) Yang-Mills theory, formulated on curved four-manifolds, in the limits of
large Nc and large 't Hooft coupling. The gravitational duals are probe
D-branes in global thermal AdS. These D-branes may undergo a topology-changing
transition in the bulk. The D-brane embeddings near the point of the topology
change exhibit a scaling symmetry. The associated scaling exponents can be
either real- or complex-valued. Which regime applies depends on the
dimensionality of a collapsing submanifold in the critical embedding. When the
scaling exponents are complex-valued, a first-order transition associated with
the flavor fields appears in the dual field theory. Real scaling exponents are
expected to be associated with a continuous transition in the dual field
theory. For one example with real exponents, the D7-brane, we study the
transition in detail. We find two field theory observables that diverge at the
critical point, and we compute the associated critical exponents. We also
present analytic and numerical evidence that the transition expresses itself in
the meson spectrum as a non-analyticity at the critical point. We argue that
the transition we study is a true phase transition only when the 't Hooft
coupling is strictly infinite.Comment: 31 pages, 21 eps files in 12 figures; v2 added one reference and one
footnote, version published in JHE
Hot Defect Superconformal Field Theory in an External Magnetic Field
In this paper we investigate the influence of an external magnetic field on a
flavoured holographic gauge theory dual to the D3/D5 intersection at finite
temperature. Our study shows that the external magnetic field has a freezing
effect on the confinement/ deconfinement phase transition. We construct the
corresponding phase diagram. We investigate some thermodynamic quantities of
the theory. A study of the entropy reveals enhanced relative jump of the
entropy at the "chiral" phase transition. A study of the magnetization shows
that both the confined and deconfined phases exhibit diamagnetic response. The
diamagnetic response in the deconfined phase has a stronger temperature
dependence reflecting the temperature dependence of the conductivity. We study
the meson spectrum of the theory and analyze the stability of the different
phases looking at both normal and quasi-normal semi-classical excitations. For
the symmetry breaking phase we analyze the corresponding pseudo-Goldstone modes
and prove that they satisfy non-relativistic dispersion relation.Comment: 42 pages, 14 figure
Universal Holographic Chiral Dynamics in an External Magnetic Field
In this work we further extend the investigation of holographic gauge
theories in external magnetic fields, continuing earlier work. We study the
phenomenon of magnetic catalysis of mass generation in 1+3 and 1+2 dimensions,
using D3/D7- and D3/D5-brane systems, respectively. We obtain the low energy
effective actions of the corresponding pseudo Goldstone bosons and study their
dispersion relations. The D3/D7 system exhibits the usual
Gell-Mann--Oakes--Renner (GMOR) relation and a relativistic dispersion
relation, while the D3/D5 system exhibits a quadratic non-relativistic
dispersion relation and a modified linear GMOR relation. The low energy
effective action of the D3/D5 system is related to that describing magnon
excitations in a ferromagnet. We also study properties of general Dp/Dq systems
in an external magnetic field and verify the universality of the magnetic
catalysis of dynamical symmetry breaking.Comment: 41 pages, 11 figures, references adde
Holographic conductivity of zero temperature superconductors
Using the recently found by G. Horowitz and M. Roberts (arXiv:0908.3677)
numerical model of the ground state of holographic superconductors (at zero
temperature), we calculate the conductivity for such models. The universal
relation connecting conductivity with the reflection coefficient was used for
finding the conductivity by the WKB approach. The dependence of the
conductivity on the frequency and charge density is discussed. Numerical
calculations confirm the general arguments of (arXiv:0908.3677) in favor of
non-zero conductivity even at zero temperature. In addition to the
Horowitz-Roberts solution we have found (probably infinite) set of extra
solutions which are normalizable and reach the same correct RN-AdS asymptotic
at spatial infinity. These extra solutions (which correspond to larger values
of the grand canonical potential) lead to effective potentials that also vanish
at the horizon and thus correspond to a non-zero conductivity at zero
temperature.Comment: 9 pages, 10 figure
Boundary and defect CFT: Open problems and applications
A review of Boundary and defect conformal field theory: open problems and applications, following a workshop held at Chicheley Hall, Buckinghamshire, UK, 7–8 Sept. 2017. We attempt to provide a broad, bird’s-eye view of the latest progress in boundary and defect conformal field theory in various sub-fields of theoretical physics, including the renormalization group, integrability, conformal bootstrap, topological field theory, supersymmetry, holographic duality, and more. We also discuss open questions and promising research directions in each of these sub-fields, and combinations thereof
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