941 research outputs found
Bifundamental Superfluids from Holography
We study the holographic dual of a (2+1)-dimensional s-wave superfluid that
breaks an abelian U(1) x U(1) global symmetry group to the diagonal U(1)_V. The
model is inspired by Sen's tachyonic action, and the operator that condenses
transforms in the bifundamental representation of the symmetry group. We focus
on two configurations: the first one describes a marginal operator, and the
phase diagram at finite temperature contains a first or a second order phase
transition, depending on the parameters that determine the theory. In the
second model the operator is relevant and the finite temperature transitions
are always second order. In the latter case the conductivity for the current
associated to the broken symmetry shows quasiparticle excitations at low
temperatures, with mass given by the width of the superconducting gap. The
suppression of spectral weight at low frequencies is also observed in the
conductivity associated to the conserved symmetry, for which the DC value
decreases as the temperature is reduced.Comment: 30 pages, 14 figures; v2: refs. added, plots and discussion improved,
typos corrected, published versio
The CP-odd sector and dynamics in holographic QCD
The holographic model of V-QCD is used to analyze the physics of QCD in the
Veneziano large-N limit. An unprecedented analysis of the CP-odd physics is
performed going beyond the level of effective field theories. The structure of
holographic saddle-points at finite is determined, as well as its
interplay with chiral symmetry breaking. Many observables (vacuum energy and
higher-order susceptibilities, singlet and non-singlet masses and mixings) are
computed as functions of and the quark mass . Wherever applicable
the results are compared to those of chiral Lagrangians, finding agreement. In
particular, we recover the Witten-Veneziano formula in the small
limit, we compute the -dependence of the pion mass and we derive the
hyperscaling relation for the topological susceptibility in the conformal
window in terms of the quark mass.Comment: 58 pages plus appendices, 19 figures. V2: section 3.1 improved, typos
corrected, published versio
V-QCD: Spectra, the dilaton and the S-parameter
Zero temperature spectra of mesons and glueballs are analyzed in a class of
holographic bottom-up models for QCD (named V-QCD), as a function of x =
N_f/N_c with the full back-reaction included. It is found that spectra are
discrete and gapped (modulo the pions) in the QCD regime, for x below the
critical value x_c where the conformal transition takes place. The masses
uniformly converge to zero in the walking region x -> x_c due to Miransky
scaling. The ratio of masses all asymptote to non-zero constants as x -> x_c
and therefore there is no "dilaton" in the spectrum. The S-parameter is
computed and found to be of O(1) in the walking regime.Comment: 11 pages, 6 figure
The discontinuities of conformal transitions and mass spectra of V-QCD
Zero temperature spectra of mesons and glueballs are analyzed in a class of
holographic bottom-up models for QCD in the Veneziano limit, N_c -> infinity,
N_f -> infinity, with x = N_f/N_c fixed (V-QCD). The backreaction of flavor on
color is fully included. It is found that spectra are discrete and gapped
(modulo the pions) in the QCD regime, for x below the critical value x_c where
the conformal transition takes place. The masses uniformly converge to zero in
the walking region x -> x_c^- due to Miransky scaling. All the ratios of masses
asymptote to non-zero constants as x -> x_c^- and therefore there is no
"dilaton" in the spectrum. The S-parameter is computed and found to be of O(1)
in units of N_f N_c in the walking regime, while it is always an increasing
function of x. This indicates the presence of a subtle discontinuity of
correlation functions across the conformal transition at x = x_c.Comment: 45 pages plus appendices, 13 figure
Holographic charge localization at brane intersections
Using gauge/gravity duality, we investigate charge localization near an
interface in a strongly coupled system. For this purpose we consider a top-down
holographic model and determine its conductivities. Our model corresponds to a
holographic interface which localizes charge around a (1+1)-dimensional defect
in a (2+1)-dimensional system. The setup consists of a D3/D5 intersection at
finite temperature and charge density. We work in the probe limit, and consider
massive embeddings of a D5-brane where the mass depends on one of the field
theory spatial directions, with a profile interpolating between a negative and
a positive value. We compute the conductivity in the direction parallel and
perpendicular to the interface. For the latter case we are able to express the
DC conductivity as a function of background horizon data. At the interface, the
DC conductivity in the parallel direction is enhanced up to five times with
respect to that in the orthogonal one. We study the implications of broken
translation invariance for the AC and DC conductivities.Comment: 36 pages, 12 figures. v2: typos corrected, JHEP versio
Executive Function and Learned Helplessness in Adolescents with Chronic Illness
Previous research has revealed that children with chronic illnesses are significantly more likely to experience academic, behavioral, and emotional difficulties. The current study hypothesized that these difficulties could be impacted by the development of learned helplessness and/or difficulties with executive functioning. The proposed theoretical model suggests that chronic illness variables have an effect on learned helplessness and executive functioning. In addition, it was hypothesized that these factors lead to an increased risk of depressive symptomatology.
The current study revealed significant differences between the chronic illness and control group in parent-reported executive function abilities; however, there were no significant differences in self-reported executive function, learned helplessness or depressive symptomatology. Parent-reported control of illness predicted parent- and self-reported executive function and parent-reported depression. It did not predict learned helplessness or self-reported depression. The number of medications taken by the chronic illness group did not predict executive function, learned helplessness, or depression. In addition, learned helplessness predicted parent- and self-reported depression. Several strong correlations were found, including associations between parent-reported executive function and self-reported executive function, and parent-reported depression and parent- and self-reported executive function. In addition, there were strong associations between self-reported executive function and parent- and self-reported depression. The model of learned helplessness, executive function, and parent-reported control of illness did not significantly predict parent-reported depression. This information may be used to improve intervention efforts directed at children with chronic illnesses
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