38 research outputs found
Ground states of holographic superconductors
We investigate the ground states of the Abelian Higgs model in AdS_4 with
various choices of parameters, and with no deformations in the ultraviolet
other than a chemical potential for the electric charge under the Abelian gauge
field. For W-shaped potentials with symmetry-breaking minima, an analysis of
infrared asymptotics suggests that the ground state has emergent conformal
symmetry in the infrared when the charge of the complex scalar is large enough.
But when this charge is too small, the likeliest ground state has Lifshitz-like
scaling in the infrared. For positive mass quadratic potentials, Lifshitz-like
scaling is the only possible infrared behavior for constant nonzero values of
the scalar. The approach to Lifshitz-like scaling is shown in many cases to be
oscillatory.Comment: 36 pages, 7 figure
Mimicking the QCD equation of state with a dual black hole
We present numerical and analytical studies of the equation of state of
translationally invariant black hole solutions to five-dimensional gravity
coupled to a single scalar. As an application, we construct a family of black
holes that closely mimics the equation of state of quantum chromodynamics at
zero chemical potential.Comment: 25 pages, 7 figure
The quantization of exotic states in SU(3) soliton models: A solvable quantum mechanical analog
The distinction between the rigid rotor and Callan-Klebanov approaches to the
quantization of SU(3) solitons is considered in the context of exotic baryons.
A numerically tractable quantum mechanical analog system is introduced to test
the reliability of the two quantization schemes. We find that in the equivalent
of the large N_c limit of QCD, the Callan-Klebanov approach agrees with a
numerical solution of the quantum mechanical analog. Rigid rotor quantization
generally does not. The implications for exotic baryons are briefly discussed.Comment: 8 pages; 3 figures; minor corrections; reference adde
An Invertible Transform for Efficient String Matching in Labeled Digraphs
Let G = (V, E) be a digraph where each vertex is unlabeled, each edge is labeled by a character in some alphabet ?, and any two edges with both the same head and the same tail have different labels. The powerset construction gives a transform of G into a weakly connected digraph G\u27 = (V\u27, E\u27) that enables solving the decision problem of whether there is a walk in G matching an arbitrarily long query string q in time linear in |q| and independent of |E| and |V|. We show G is uniquely determined by G\u27 when for every v_? ? V, there is some distinct string s_? on ? such that v_? is the origin of a closed walk in G matching s_?, and no other walk in G matches s_? unless it starts and ends at v_?. We then exploit this invertibility condition to strategically alter any G so its transform G\u27 enables retrieval of all t terminal vertices of walks in the unaltered G matching q in O(|q| + t log |V|) time. We conclude by proposing two defining properties of a class of transforms that includes the Burrows-Wheeler transform and the transform presented here
Pion-Nucleon Scattering Relations at Next-to-Leading Order in 1/N_c
We obtain relations between partial-wave amplitudes for pi-N-->pi-N and
pi-N-->pi-Delta directly from large N_c QCD. While linear relations among
certain amplitudes holding at leading order (LO) in 1/N_c were derived in the
context of chiral soliton models two decades ago, the present work employs a
fully model-independent framework based on consistency with the large N_c
expansion. At LO we reproduce the soliton model results; however, this method
allows for systematic corrections. At next-to-leading order (NLO), most
relations require additional unknown functions beyond those appearing at
leading order (LO) and thus have little additional predictive power. However,
three NLO relations for the pi-N-->pi-Delta reaction are independent of unknown
functions and make predictions accurate at this order. The amplitudes relevant
to two of these relations were previously extracted from experiment. These
relations describe experiment dramatically better than their LO counterparts.Comment: 8 pages, 2 figures; references adde
NSeq: a multithreaded Java application for finding positioned nucleosomes from sequencing data
We introduce NSeq, a fast and efficient Java application for finding positioned nucleosomes from the high-throughput sequencing of MNase-digested mononucleosomal DNA. NSeq includes a user-friendly graphical interface, computes false discovery rates (FDRs) for candidate nucleosomes from Monte Carlo simulations, plots nucleosome coverage and centers, and exploits the availability of multiple processor cores by parallelizing its computations. Java binaries and source code are freely available at https://github.com/songlab/NSeq. The software is supported on all major platforms equipped with Java Runtime Environment 6 or later
A bound on the speed of sound from holography
We show that the squared speed of sound v_{s}^{2} is bounded from above at
high temperatures by the conformal value of 1/3 in a class of strongly coupled
four-dimensional field theories, given some mild technical assumptions. This
class consists of field theories that have gravity duals sourced by a single
scalar field. There are no known examples to date of field theories with
gravity duals for which v_{s}^{2} exceeds 1/3 in energetically favored
configurations. We conjecture that v_{s}^{2}=1/3 represents an upper bound for
a broad class of four-dimensional theories.Comment: 4 pages, 1 figur
Thermodynamics and bulk viscosity of approximate black hole duals to finite temperature quantum chromodynamics
We consider classes of translationally invariant black hole solutions whose
equations of state closely resemble that of QCD at zero chemical potential. We
use these backgrounds to compute the ratio zeta/s of bulk viscosity to entropy
density. For a class of black holes that exhibits a first order transition, we
observe a sharp rise in zeta/s near T_c. For constructions that exhibit a
smooth cross-over, like QCD does, the rise in zeta/s is more modest. We
conjecture that divergences in zeta/s for black hole horizons are related to
extrema of the entropy density as a function of temperature.Comment: 5 pages, 1 figur