499 research outputs found
Holography of the Conformal Window
Inspired by the model of Jarvinen and Kiritsis, we present a simple
holographic model for the on set of chiral symmetry breaking at the edge of the
conformal window in QCD in the Veneziano limit. Our most naive model enforces
the QCD two loop running coupling on a D3/D7 holographic brane system. The mass
of the holographic field, describing the chiral condensate in the model, is
driven below the BF bound when the running is sufficiently strong, triggering
chiral symmetry breaking for N_f/N_c<2.9. This model though contains too great
a remnant of supersymmetry and does not correctly encode the perturbative
anomalous dimensions of QCD. In a second model we impose the QCD anomalous
dimension result and find chiral symmetry breaking sets in for N_f/N_c=4 at a
BKT-type phase transition. In this case the transition is triggered when the
anomalous dimension of the mass operator \gamma_m=1.Comment: 10 pages, 2 figures, v2: minor corrections, improved Figure
Non Mean-Field Quantum Critical Points from Holography
We construct a class of quantum critical points with non-mean-field critical
exponents via holography. Our approach is phenomenological. Beginning with the
D3/D5 system at nonzero density and magnetic field which has a chiral phase
transition, we simulate the addition of a third control parameter. We then
identify a line of quantum critical points in the phase diagram of this theory,
provided that the simulated control parameter has dimension less than two. This
line smoothly interpolates between a second-order transition with mean-field
exponents at zero magnetic field to a holographic
Berezinskii-Kosterlitz-Thouless transition at larger magnetic fields. The
critical exponents of these transitions only depend upon the parameters of an
emergent infrared theory. Moreover, the non-mean-field scaling is destroyed at
any nonzero temperature. We discuss how generic these transitions are.Comment: 15 pages, 7 figures, v2: Added reference
The Chiral Model of Sakai-Sugimoto at Finite Baryon Density
In the context of holographic QCD we analyze Sakai-Sugimoto's chiral model at
finite baryon density and zero temperature. The baryon number density is
introduced through compact D4 wrapping S^4 at the tip of D8-\bar{D8}. Each
baryon acts as a chiral point-like source distributed uniformly over R^3, and
leads a non-vanishing U(1)_V potential on the brane. For fixed baryon charge
density n_B we analyze the bulk energy density and pressure using the canonical
formalism. The baryonic matter with point like sources is always in the
spontaneously broken phase of chiral symmetry, whatever the density. The
point-like nature of the sources and large N_c cause the matter to be repulsive
as all baryon interactions are omega mediated. Through the induced DBI action
on D8-\bar{D8}, we study the effects of the fixed baryon charge density n_B on
the pion and vector meson masses and couplings. Issues related to vector
dominance in matter in the context of holographic QCD are also discussed.Comment: V3: 39 pages, 16 figures, minor corrections, version to appear in
JHEP. V2: references added, typos correcte
Baryonic Response of Dense Holographic QCD
The response function of a homogeneous and dense hadronic system to a
time-dependent (baryon) vector potential is discussed for holographic dense QCD
(D4/D8 embedding) both in the confined and deconfined phases. Confined
holographic QCD is an uncompressible and static baryonic insulator at large N_c
and large \lambda, with a gapped vector spectrum and a massless pion.
Deconfined holographic QCD is a diffusive conductor with restored chiral
symmetry and a gapped transverse baryonic current. Similarly, dense D3/D7 is
diffusive for any non-zero temperature at large N_c and large \lambda. At zero
temperature dense D3/D7 exhibits a baryonic longitudinal visco-elastic mode
with a first sound speed \lambda/\sqrt{3} and a small width due to a shear
viscosity to baryon ratio \eta/n_B=\hbar/4. This mode is turned diffusive by
arbitrarily small temperatures, a hallmark of holography.Comment: V2: 47 pages, 7 figures, references added, typos correcte
Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide
The surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a
(
LaFe
O
3
)
8
/
(
SrFe
O
3
)
1
superlattice film capped with four layers of
LaFe
O
3
. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from
F
e
3
+
in the bulk to
F
e
2
+
at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen
Towards spin-polarized two-dimensional electron gas at a surface of an antiferromagnetic insulating oxide
The surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a
(
LaFe
O
3
)
8
/
(
SrFe
O
3
)
1
superlattice film capped with four layers of
LaFe
O
3
. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from
F
e
3
+
in the bulk to
F
e
2
+
at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen
Temporal Trends of Emergency Department Visits of Patients with Atrial Fibrillation:A Nationwide Population-Based Study
The question of list decoding error-correcting codes over finite fields (under the Hamming metric) has been widely studied in recent years. Motivated by the similar discrete linear structure of linear codes and point lattices in R N, and their many shared applications across complexity theory, cryptography, and coding theory, we initiate the study of list decoding for lattices. Namely: for a lattice L ⊆ R N, given a target vector r ∈ R N and a distance parameter d, output the set of all lattice points w ∈ L that are within distance d of r. In this work we focus on combinatorial and algorithmic questions related to list decoding for the well-studied family of Barnes-Wall lattices. Our main contributions are twofold: 1. We give tight (up to polynomials) combinatorial bounds on the worst-case list size, showing it to be polynomial in the lattice dimension for any error radius bounded away from the lattice’s minimum distance (in the Euclidean norm). 2. Building on the unique decoding algorithm of Micciancio and Nicolosi (ISIT ’08), we give a list-decoding algorithm that runs in time polynomial in the lattice dimension and worst-case list size, for any error radius. Moreover, our algorithm is highly parallelizable, and with sufficiently many processors can run in parallel time only poly-logarithmic in the lattice dimension. In particular, our results imply a polynomial-time list-decoding algorithm for any error radius bounded away from the minimum distance, thus beating a typical barrier for natural error-correcting codes posed by the Johnson radius
Impact of mental disorders on the risk of atrial fibrillation in patients with diabetes mellitus:a nationwide population-based study
BACKGROUND: It is unclear whether mental disorders are an independent risk factor for atrial fibrillation (AF) in patients with diabetes. We aimed to investigate whether patients with diabetes who have mental disorders have an increased risk for AF. METHODS: Using the Korea National Health Insurance Service database, we enrolled 2,512,690 patients diagnosed with diabetes without AF between 2009 and 2012. We assessed five mental disorders: depression, insomnia, anxiety, bipolar disorder, and schizophrenia. Newly diagnosed AF was identified during the follow-up period, and multivariate Cox regression analysis was performed. RESULTS: Among the 2,512,690 patients (mean age 57.2 ± 12.3 years; 60.1% men), 828,929 (33.0%) had mental disorders. Among the five mental disorders, anxiety (68.1%) was the most common, followed by insomnia (40.0%). During a median follow-up duration of 7.1 years, new-onset AF was diagnosed in 79,525 patients (4.66 per 1,000 person-years). Patients with diabetes who had mental disorders showed a higher risk for AF (adjusted hazard ratio [HR] 1.19; 95% confidence interval [CI] 1.17–1.21; p-value < 0.001). Depression, insomnia, and anxiety were significantly associated with higher risk for AF (adjusted HR [95% CI]: 1.15 [1.12–1.17], 1.15 [1.13–1.18], and 1.19 [1.67–1.21], respectively; all p-values < 0.001), whereas bipolar disorder and schizophrenia were not. CONCLUSIONS: Mental disorders, especially depression, insomnia, and anxiety, were associated with an increased risk for AF in patients with diabetes. Greater awareness with a prompt diagnosis of AF should be considered for patients with both DM and mental disorders. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12933-022-01682-7
Holographic DC conductivities from the open string metric
We study the DC conductivities of various holographic models using the open
string metric (OSM), which is an effective metric geometrizing density and
electromagnetic field effect. We propose a new way to compute the nonlinear
conductivity using OSM. As far as the final conductivity formula is concerned,
it is equivalent to the Karch-O'Bannon's real-action method. However, it yields
a geometrical insight and technical simplifications. Especially, a real-action
condition is interpreted as a regular geometry condition of OSM. As
applications of the OSM method, we study several holographic models on the
quantum Hall effect and strange metal. By comparing a Lifshitz background and
the Light-Cone AdS, we show how an extra parameter can change the temperature
scaling behavior of conductivity. Finally we discuss how OSM can be used to
study other transport coefficients, such as diffusion constant, and effective
temperature induced by the effective world volume horizon.Comment: 33 page
Chiral phase transitions and quantum critical points of the D3/D7(D5) system with mutually perpendicular E and B fields at finite temperature and density
We study chiral symmetry restoration with increasing temperature and density
in gauge theories subject to mutually perpendicular electric and magnetic
fields using holography. We determine the chiral symmetry breaking phase
structure of the D3/D7 and D3/D5 systems in the temperature-density-electric
field directions. A magnetic field may break the chiral symmetry and an
additional electric field induces Ohm and Hall currents as well as restoring
the chiral symmetry. At zero temperature the D3/D5 system displays a line of
holographic BKT phase transitions in the density-electric field plane, while
the D3/D7 system shows a mean-field phase transition. At intermediate
temperatures, the transitions in the density-electric field plane are of first
order at low density, transforming to second order at critical points as
density rises. At high temperature the transition is only ever first order.Comment: 15 pages, 7 figures, v2: Added a referenc
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