256 research outputs found
Quantum Critical Superfluid Flows and Anisotropic Domain Walls
We construct charged anisotropic AdS domain walls as solutions of a
consistent truncation of type IIB string theory. These are a one-parameter
family of solutions that flow to an AdS fixed point in the IR, exhibiting
emergent conformal invariance and quantum criticality. They represent the
zero-temperature limit of the holographic superfluids at finite superfluid
velocity constructed in arXiv:1010.5777. We show that these domain walls exist
only for velocities less than a critical value, agreeing in detail with a
conjecture made there. We also comment about the IR limits of flows with
velocities higher than this critical value, and point out an intriguing
similarity between the phase diagrams of holographic superfluid flows and those
of ordinary superconductors with imbalanced chemical potential.Comment: 11 pages, 3 figures. V2: Very minor corrections. JHEP versio
Flavor from M5-branes
We study various aspects of the defect conformal field theory that arises
when placing a single M5-brane probe in AdS_4 x S^7. We derive the full set of
fluctuation modes and dimensions of the corresponding dual operators. We argue
that the latter does not depend on the presence of a non-trivial magnetic flux
on the M5-brane world-volume. Finally we give a mass to the hypermultiplet
living on the defect, and compute the resulting mesonic spectrum.Comment: 19 page
On the geometry of string duals with backreacting flavors
Making use of generalized calibrated geometry and G-structures we put the
problem of finding string-duals with smeared backreacting flavor branes in a
more mathematical setting. This more formal treatment of the problem allows us
to easily smear branes without good coordinate representations, establish
constraints on the smearing form and identify a topological central charge in
the SUSY algebra. After exhibiting our methods for a series of well known
examples, we apply them to the problem of flavoring a supergravity-dual to a
d=2+1 dimensional N=2 super Yang-Mills-like theory. We find new solutions to
both the flavored and unflavored systems. Interpretating these turns out to be
difficult.Comment: 38 pages - Typos corrected and references added - As published in
JHE
On unquenched N=2 holographic flavor
The addition of fundamental degrees of freedom to a theory which is dual (at
low energies) to N=2 SYM in 1+3 dimensions is studied. The gauge theory lives
on a stack of Nc D5 branes wrapping an S^2 with the appropriate twist, while
the fundamental hypermultiplets are introduced by adding a different set of Nf
D5-branes. In a simple case, a system of first order equations taking into
account the backreaction of the flavor branes is derived (Nf/Nc is kept of
order 1). From it, the modification of the holomorphic coupling is computed
explicitly. Mesonic excitations are also discussed.Comment: 25 pages, 4 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
Pain severity predicts depressive symptoms over and above individual illnesses and multimorbidity in older adults.
BACKGROUND: Multi-morbidity in older adults is commonly associated with depressed mood. Similarly, subjective reports of pain are also associated with both physical illness and increased depressive symptoms. However, whether pain independently contributes to the experience of depression in older people with multi-morbidity has not been studied. METHODS: In this study, participants were 1281 consecutive older adults presenting to one of 19 primary care services in Australia (recruitment rate = 75%). Participants were asked to indicate the presence of a number of common chronic illnesses, to rate their current pain severity and to complete the Geriatric Depression Scale. RESULTS: Results confirmed that the number of medical illnesses reported was strongly associated with depressive symptoms. Twenty-six percent of participants with multi-morbidity scored in the clinical range for depressive symptoms in comparison to 15% of participants with no illnesses or a single illness. In regression analyses, the presence of chronic pain (t = 5.969, p < 0.0005), diabetes (t = 4.309, p < 0.0005), respiratory (t = 3.720, p < 0.0005) or neurological illness (t = 2.701, p = 0.007) were all independent contributors to depressive symptoms. Even when controlling for each individual illness, and the overall number of illnesses (t = 2.207, p = 0.028), pain severity remained an independent predictor of depressed mood (F change = 28.866, p < 0.0005, t = 5.373, p < 0.0005). CONCLUSIONS: Physicians should consider screening for mood problems amongst those with multi-morbidity, particularly those who experience pain
The shear viscosity of the non-commutative plasma
We compute the shear viscosity of the non-commutative N=4 super Yang-Mills
quantum field theory at strong coupling using the dual supergravity background.
Special interest derives from the fact that the background presents an
intrinsic anisotropy in space through the distinction of commutative and
non-commutative directions. Despite this anisotropy the analysis exhibits the
ubiquitous result \eta/s = 1/4\pi for two different shear channels. In order to
derive this result, we show that the boundary energy momentum tensor must
couple to the open string metric. As a byproduct we compute the renormalised
holographic energy momentum tensor and show that it coincides with one in the
commutative theory.Comment: 17 pages. v2: reference adde
The Many Phases of Holographic Superfluids
We investigate holographic superfluids in AdS_{d+1} with d=3,4 in the
non-backreacted approximation for various masses of the scalar field. In d=3
the phase structure is universal for all the masses that we consider: the
critical temperature decreases as the superfluid velocity increases, and as it
is cranked high enough, the order of the phase transition changes from second
to first. Surprisingly, in d=4 we find that the phase structure is more
intricate. For sufficiently high mass, there is always a second order phase
transition to the normal phase, no matter how high the superfluid velocity. For
some parameters, as we lower the temperature, this transition happens before a
first order transition to a new superconducting phase. Across this first order
transition, the gap in the transverse conductivity jumps from almost zero to
about half its maximum value. We also introduce a double scaling limit where we
can study the phase transitions (semi-)analytically in the large velocity
limit. The results corroborate and complement our numerical results. In d=4,
this approach has the virtue of being fully analytically tractable.Comment: 31 pages, 19 figure
Type IIB Holographic Superfluid Flows
We construct fully backreacted holographic superfluid flow solutions in a
five-dimensional theory that arises as a consistent truncation of low energy
type IIB string theory. We construct a black hole with scalar and vector hair
in this theory, and study the phase diagram. As expected, the superfluid phase
ceases to exist for high enough superfluid velocity, but we show that the phase
transition between normal and superfluid phases is always second order. We also
analyze the zero temperature limit of these solutions. Interestingly, we find
evidence that the emergent IR conformal symmetry of the zero-temperature domain
wall is broken at high enough velocity.Comment: v3: Published version. Figures 5 and 6 corrected. 24 pages, 7 figure
Holographic flavor in N=4 gauge theories in 3d from wrapped branes
We study the addition of flavor to the gravity dual of N=4 three-dimensional
gauge theories obtained by wrapping D4-branes on a two-cycle of a
non-compact Calabi-Yau two-fold. In this setup the flavor is introduced by
adding another set of D4-branes that are extended along the non-compact
directions of the Calabi-Yau which are normal to the cycle which the color
branes wrap. The analysis is performed both in the quenched and unquenched
approximations. In this latter case we compute the backreacted metric and we
show that it reproduces the running of the gauge coupling. The meson spectrum
and the behavior of Wilson loops are also discussed and the holographic
realization of the Higgs branch is analyzed. Other aspects of this system
studied are the entanglement entropy and the non-relativistic version of our
backgrounds.Comment: 44 pages, 6 figure
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