13,355 research outputs found
Towards a holographic realization of the quarkyonic phase
Large-N_c QCD matter at intermediate baryon density and low temperatures has
been conjectured to be in the so-called quarkyonic phase, i.e., to have a quark
Fermi surface and on top of it a confined spectrum of excitations. It has been
suggested that the presence of the quark Fermi surface leads to a homogeneous
phase with restored chiral symmetry, which is unstable towards creating
condensates breaking both the chiral and translational symmetry. Motivated by
these exotic features, we investigate properties of cold baryonic matter in the
single flavor Sakai-Sugimoto model searching for a holographic realization of
the quarkyonic phase. We use a simplified mean-field description and focus on
the regime of parametrically large baryon densities, of the order of the square
of the 't Hooft coupling, as they turn out to lead to new physical effects
similar to the ones occurring in the quarkyonic phase. One effect, the
appearance of a particular marginally stable mode breaking translational
invariance and linked with the presence of the Chern-Simons term in the flavor
brane Lagrangian, is known to occur in the deconfined phase of the
Sakai-Sugimoto model, but turns out to be absent here. The other, completely
new phenomenon that we, preliminarily, study using strong simplifying
assumptions are density-enhanced interactions of the flavor brane gauge field
with holographically represented baryons. These seem to significantly affect
the spectrum of vector and axial mesons and might lead to approximate chiral
symmetry restoration in the lowest part of the spectrum, where the mesons start
to qualitatively behave like collective excitations of the dense baryonic
medium. We discuss the relevance of these effects for holographic searches of
the quarkyonic phase and conclude with a discussion of various subtleties
involved in constructing a mean-field holographic description of a dense
baryonic medium.Comment: 31 pages, 16 figures; v2: inset plot in Fig. 10 removed, coloring in
Fig. 13 fixed, typos fixed, matches published versio
Entanglement, Holography and Causal Diamonds
We argue that the degrees of freedom in a d-dimensional CFT can be
re-organized in an insightful way by studying observables on the moduli space
of causal diamonds (or equivalently, the space of pairs of timelike separated
points). This 2d-dimensional space naturally captures some of the fundamental
nonlocality and causal structure inherent in the entanglement of CFT states.
For any primary CFT operator, we construct an observable on this space, which
is defined by smearing the associated one-point function over causal diamonds.
Known examples of such quantities are the entanglement entropy of vacuum
excitations and its higher spin generalizations. We show that in holographic
CFTs, these observables are given by suitably defined integrals of dual bulk
fields over the corresponding Ryu-Takayanagi minimal surfaces. Furthermore, we
explain connections to the operator product expansion and the first law of
entanglement entropy from this unifying point of view. We demonstrate that for
small perturbations of the vacuum, our observables obey linear two-derivative
equations of motion on the space of causal diamonds. In two dimensions, the
latter is given by a product of two copies of a two-dimensional de Sitter
space. For a class of universal states, we show that the entanglement entropy
and its spin-three generalization obey nonlinear equations of motion with local
interactions on this moduli space, which can be identified with Liouville and
Toda equations, respectively. This suggests the possibility of extending the
definition of our new observables beyond the linear level more generally and in
such a way that they give rise to new dynamically interacting theories on the
moduli space of causal diamonds. Various challenges one has to face in order to
implement this idea are discussed.Comment: 84 pages, 12 figures; v2: expanded discussion on constraints in
section 7, matches published versio
Characterizing time-irreversibility in disordered fermionic systems by the effect of local perturbations
We study the effects of local perturbations on the dynamics of disordered
fermionic systems in order to characterize time-irreversibility. We focus on
three different systems, the non-interacting Anderson and Aubry-Andr\'e-Harper
(AAH-) models, and the interacting spinless disordered t-V chain. First, we
consider the effect on the full many-body wave-functions by measuring the
Loschmidt echo (LE). We show that in the extended/ergodic phase the LE decays
exponentially fast with time, while in the localized phase the decay is
algebraic. We demonstrate that the exponent of the decay of the LE in the
localized phase diverges proportionally to the single-particle localization
length as we approach the metal-insulator transition in the AAH model. Second,
we probe different phases of disordered systems by studying the time
expectation value of local observables evolved with two Hamiltonians that
differ by a spatially local perturbation. Remarkably, we find that many-body
localized systems could lose memory of the initial state in the long-time
limit, in contrast to the non-interacting localized phase where some memory is
always preserved
Scarring by homoclinic and heteroclinic orbits
In addition to the well known scarring effect of periodic orbits, we show
here that homoclinic and heteroclinic orbits, which are cornerstones in the
theory of classical chaos, also scar eigenfunctions of classically chaotic
systems when associated closed circuits in phase space are properly quantized,
thus introducing strong quantum correlations. The corresponding quantization
rules are also established. This opens the door for developing computationally
tractable methods to calculate eigenstates of chaotic systems.Comment: 5 pages, 4 figure
A hole-ographic spacetime
We embed spherical Rindler space -- a geometry with a spherical hole in its
center -- in asymptotically AdS spacetime and show that it carries a
gravitational entropy proportional to the area of the hole. Spherical
AdS-Rindler space is holographically dual to an ultraviolet sector of the
boundary field theory given by restriction to a strip of finite duration in
time. Because measurements have finite durations, local observers in the field
theory can only access information about bounded spatial regions. We propose a
notion of Residual Entropy that captures uncertainty about the state of a
system left by the collection of local, finite-time observables. For
two-dimensional conformal field theories we use holography and the strong
subadditivity of entanglement to propose a formula for Residual Entropy and
show that it precisely reproduces the areas of circular holes in AdS3.
Extending the notion to field theories on strips with variable durations in
time, we show more generally that Residual Entropy computes the areas of all
closed, inhomogenous curves on a spatial slice of AdS3. We discuss the
extension to higher dimensional field theories, the relation of Residual
Entropy to entanglement between scales, and some implications for the emergence
of space from the RG flow of entangled field theories.Comment: v3: minor typos correcte
Topological Susceptibility and Zero Mode Size in Lattice QCD
We use the overlap formalism to define a topological index on the lattice. We
study the spectral flow of the hermitian Wilson-Dirac operator and identify
zero crossings with topological objects. We determine the topological
susceptibility and zero mode size distribution, and we comment on the stability
of our results.Comment: 3 pages latex with 2 postscript figures. Talk presented at
LATTICE98(confine
Orbit bifurcations and the scarring of wavefunctions
We extend the semiclassical theory of scarring of quantum eigenfunctions
psi_{n}(q) by classical periodic orbits to include situations where these
orbits undergo generic bifurcations. It is shown that |psi_{n}(q)|^{2},
averaged locally with respect to position q and the energy spectrum E_{n}, has
structure around bifurcating periodic orbits with an amplitude and length-scale
whose hbar-dependence is determined by the bifurcation in question.
Specifically, the amplitude scales as hbar^{alpha} and the length-scale as
hbar^{w}, and values of the scar exponents, alpha and w, are computed for a
variety of generic bifurcations. In each case, the scars are semiclassically
wider than those associated with isolated and unstable periodic orbits;
moreover, their amplitude is at least as large, and in most cases larger. In
this sense, bifurcations may be said to give rise to superscars. The
competition between the contributions from different bifurcations to determine
the moments of the averaged eigenfunction amplitude is analysed. We argue that
there is a resulting universal hbar-scaling in the semiclassical asymptotics of
these moments for irregular states in systems with a mixed phase-space
dynamics. Finally, a number of these predictions are illustrated by numerical
computations for a family of perturbed cat maps.Comment: 24 pages, 6 Postscript figures, corrected some typo
Star Formation in Dwarf Galaxies
We explore mechanisms for the regulation of star formation in dwarf galaxies.
We concentrate primarily on a sample in the Virgo cluster, which has HI and
blue total photometry, for which we collected H data at the Wise
Observatory. We find that dwarf galaxies do not show the tight correlation of
the surface brightness of H (a star formation indicator) with the HI
surface density, or with the ratio of this density to a dynamical timescale, as
found for large disk or starburst galaxies. On the other hand, we find the
strongest correlation to be with the average blue surface brightness,
indicating the presence of a mechanism regulating the star formation by the
older (up to 1 Gyr) stellar population if present, or by the stellar population
already formed in the present burst.Comment: 15 pages (LATEX aasms4 style) and three postscript figures, accepted
for publication in the Astrophysical Journa
Dissecting Galaxy Formation: II. Comparing Substructure in Pure Dark Matter and Baryonic Models
We compare the substructure evolution in pure dark matter (DM) halos with
those in the presence of baryons (PDM and BDM). The prime halos have been
analyzed by Romano-Diaz et al (2009). Models have been evolved from identical
initial conditions using Constrained Realizations, including star formation and
feedback. A comprehensive catalog of subhalos has been compiled and properties
of subhalos analyzed in the mass range of 10^8 Mo - 10^11 Mo. We find that
subhalo mass functions are consistent with a single power law, M_sbh^{alpha},
but detect a nonnegligible shift between these functions, alpha -0.86 for the
PDM, and -0.98 for the BDM. Overall, alpha const. in time with variations of
+-15%. Second, we find that the radial mass distribution of subhalos can be
approximated by a power law, R^{gamma} with a steepening around the radius of a
maximal circular velocity, Rvmax, in the prime halos. Gamma ~-1.5 for the PDM
and -1 for the BDM, inside Rvmax, and is steeper outside. We detect little
spatial bias between the subhalo populations and the DM of the main halos. The
subhalo population exhibits much less triaxiality with baryons, in tandem with
the prime halo. Finally, we find that, counter-intuitively, the BDM population
is depleted at a faster rate than the PDM one within the central 30kpc of the
prime. Although the baryons provide a substantial glue to the subhalos, the
main halos exhibit the same trend. This assures a more efficient tidal
disruption of the BDM subhalos. This effect can be reversed for a more
efficient feedback from stellar evolution and supermassive black holes, which
will expel baryons from the center and decrease the concentration of the prime
halo. We compare our results with via Lactea and Aquarius simulations and other
published results.Comment: 12 pages, 9 figures, to be published by the Astrophysical Journa
The Central Region in M100: Observations and Modeling
We present new high-resolution observations of the center of the late-type
spiral M100 (NGC 4321) supplemented by 3D numerical modeling of stellar and gas
dynamics, including star formation (SF). NIR imaging has revealed a stellar
bar, previously inferred from optical and 21 cm observations, and an
ovally-shaped ring-like structure in the plane of the disk. The K isophotes
become progressively elongated and skewed to the position angle of the bar
(outside and inside the `ring') forming an inner bar-like region. The galaxy
exhibits a circumnuclear starburst in the inner part of the K `ring'. Two
maxima of the K emission have been observed to lie symmetrically with respect
to the nucleus and equidistant from it slightly leading the stellar bar. We
interpret the twists in the K isophotes as being indicative of the presence of
a double inner Lindblad resonance (ILR) and test this hypothesis by modeling
the gas flow in a self-consistent gas + stars disk embedded in a halo, with an
overall NGC4321-like mass distribution. We have reproduced the basic morphology
of the region (the bar, the large scale trailing shocks, two symmetric K peaks
corresponding to gas compression maxima which lie at the caustic formed by the
interaction of a pair of trailing and leading shocks in the vicinity of the
inner ILR, both peaks being sites of SF, and two additional zones of SF
corresponding to the gas compression maxima, referred usually as `twin peaks').Comment: 31 pages, postscript, compressed, uuencoded. 21 figures available in
postscript, compressed form by anonymous ftp from
ftp://asta.pa.uky.edu/shlosman/main100 , mget *.ps.Z. To appear in Ap.
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