547 research outputs found
Critical behavior of O(2)xO(N) symmetric models
We investigate the controversial issue of the existence of universality
classes describing critical phenomena in three-dimensional statistical systems
characterized by a matrix order parameter with symmetry O(2)xO(N) and
symmetry-breaking pattern O(2)xO(N) -> O(2)xO(N-2). Physical realizations of
these systems are, for example, frustrated spin models with noncollinear order.
Starting from the field-theoretical Landau-Ginzburg-Wilson Hamiltonian, we
consider the massless critical theory and the minimal-subtraction scheme
without epsilon expansion. The three-dimensional analysis of the corresponding
five-loop expansions shows the existence of a stable fixed point for N=2 and
N=3, confirming recent field-theoretical results based on a six-loop expansion
in the alternative zero-momentum renormalization scheme defined in the massive
disordered phase.
In addition, we report numerical Monte Carlo simulations of a class of
three-dimensional O(2)xO(2)-symmetric lattice models. The results provide
further support to the existence of the O(2)xO(2) universality class predicted
by the field-theoretical analyses.Comment: 45 pages, 20 figs, some additions, Phys.Rev.B in pres
Exploiting gauge and constraint freedom in hyperbolic formulations of Einstein's equations
We present new many-parameter families of strongly and symmetric hyperbolic
formulations of Einstein's equations that include quite general algebraic and
live gauge conditions for the lapse. The first system that we present has 30
variables and incorporates an algebraic relationship between the lapse and the
determinant of the three metric that generalizes the densitized lapse
prescription. The second system has 34 variables and uses a family of live
gauges that generalizes the Bona-Masso slicing conditions. These systems have
free parameters even after imposing hyperbolicity and are expected to be useful
in 3D numerical evolutions. We discuss under what conditions there are no
superluminal characteristic speeds
Entanglement entropy of two dimensional systems and holography
In this note a new method for computing the entanglement entropy of a CFT
holographically is explored. It consists of finding a bulk background with a
boundary metric that has the conical singularities needed to compute the
entanglement entropy in the usual QFT definition. An explicit calculation is
presented for d=2.Comment: 20 pages, 1 figure: v2 typos fixed, references and comments adde
Well-Posed Initial-Boundary Evolution in General Relativity
Maximally dissipative boundary conditions are applied to the initial-boundary
value problem for Einstein's equations in harmonic coordinates to show that it
is well-posed for homogeneous boundary data and for boundary data that is small
in a linearized sense. The method is implemented as a nonlinear evolution code
which satisfies convergence tests in the nonlinear regime and is robustly
stable in the weak field regime. A linearized version has been stably matched
to a characteristic code to compute the gravitational waveform radiated to
infinity.Comment: 5 pages, 6 figures; added another convergence plot to Fig. 2 + minor
change
AdS/CFT and Strong Subadditivity of Entanglement Entropy
Recently, a holographic computation of the entanglement entropy in conformal
field theories has been proposed via the AdS/CFT correspondence. One of the
most important properties of the entanglement entropy is known as the strong
subadditivity. This requires that the entanglement entropy should be a concave
function with respect to geometric parameters. It is a non-trivial check on the
proposal to see if this property is indeed satisfied by the entropy computed
holographically. In this paper we examine several examples which are defined by
annuli or cusps, and confirm the strong subadditivity via direct calculations.
Furthermore, we conjecture that Wilson loop correlators in strongly coupled
gauge theories satisfy the same relation. We also discuss the relation between
the holographic entanglement entropy and the Bousso bound.Comment: 29 pages, harvmac, 7 figures, references adde
Chiral phase transitions: focus driven critical behavior in systems with planar and vector ordering
The fixed point that governs the critical behavior of magnets described by
the -vector chiral model under the physical values of () is
shown to be a stable focus both in two and three dimensions. Robust evidence in
favor of this conclusion is obtained within the five-loop and six-loop
renormalization-group analysis in fixed dimension. The spiral-like approach of
the chiral fixed point results in unusual crossover and near-critical regimes
that may imitate varying critical exponents seen in physical and computer
experiments.Comment: 4 pages, 5 figures. Discussion enlarge
Multimodal long noncoding RNA interaction networks: Control panels for cell fate specification
Lineage specification in early development is the basis for the exquisitely precise body plan of multicellular organisms. It is therefore critical to understand cell fate decisions in early development. Moreover, for regenerative medicine, the accurate specification of cell types to replace damaged/diseased tissue is strongly dependent on identifying determinants of cell identity. Long noncoding RNAs (lncRNAs) have been shown to regulate cellular plasticity, including pluripotency establishment and maintenance, differentiation and development, yet broad phenotypic analysis and the mechanistic basis of their function remains lacking. As components of molecular condensates, lncRNAs interact with almost all classes of cellular biomolecules, including proteins, DNA, mRNAs, and microRNAs. With functions ranging from controlling alternative splicing of mRNAs, to providing scaffolding upon which chromatin modifiers are assembled, it is clear that at least a subset of lncRNAs are far from the transcriptional noise they were once deemed. This review highlights the diversity of lncRNA interactions in the context of cell fate specification, and provides examples of each type of interaction in relevant developmental contexts. Also highlighted are experimental and computational approaches to study lncRNAs
Entanglement and Nonunitary Evolution
We consider a collapsing relativistic spherical shell for a free quantum
field. Once the center of the wavefunction of the shell passes a certain radius
R, the degrees of freedom inside R are traced over. We show that an observer
outside this region will determine that the evolution of the system is
nonunitary. We argue that this phenomenon is generic to entangled systems, and
discuss a possible relation to black hole physics.Comment: 14 pages, 1 figure; Added a clarification regarding the relation with
black hole physic
SWI/SNF remains localized to chromatin in the presence of SCHLAP1
SCHLAP1 is a long noncoding RNA that is reported to function by depleting the SWI/SNF complex from the genome. We investigated the hypothesis that SCHLAP1 affects only specific compositions of SWI/SNF. Using several assays, we found that SWI/SNF is not depleted from the genome by SCHLAP1 and that SWI/SNF is associated with many coding and noncoding RNAs, suggesting that SCHLAP1 may function in a SWI/SNF-independent manner
On String Theory Duals of Lifshitz-like Fixed Points
We present type IIB supergravity solutions which are expected to be dual to
certain Lifshitz-like fixed points with anisotropic scale invariance. They are
expected to describe a class of D3-D7 systems and their finite temperature
generalizations are straightforward. We show that there exist solutions that
interpolate between these anisotropic solutions in the IR and the standard AdS5
solutions in the UV. This predicts anisotropic RG flows from familiar isotropic
fixed points to anisotropic ones. In our case, these RG flows are triggered by
a non-zero theta-angle in Yang-Mills theories that linearly depends on one of
the spatial coordinates. We study the perturbations around these backgrounds
and discuss the possibility of instability. We also holographically compute
their thermal entropies, viscosities, and entanglement entropies.Comment: 47 pages, 4 figure
- …