6,372 research outputs found
Quantum criticality in SU(3) and SU(4) anti-ferromagnets
We study the quantum phase transition out of the Neel state in SU(3) and
SU(4) generalizations of the Heisenberg anti-ferromagnet with a sign problem
free four spin coupling (so-called JQ model), by extensive quantum Monte Carlo
simulations. We present evidence that the SU(3) and SU(4) order parameters and
the SU(3) and SU(4) stiffness' go to zero continuously without any evidence for
a first order transition. However, we find considerable deviations from simple
scaling laws for the stiffness even in the largest system sizes studied. We
interpret these as arising from multiplicative scaling terms in these
quantities which affect the leading behavior, i.e., they will persist in the
thermodynamic limit unlike the conventional additive corrections from
irrelevant operators. We conjecture that these multiplicative terms arise from
dangerously irrelevant operators whose contributions to the quantities of
interest are non-analytic
Holst Actions for Supergravity Theories
Holst action containing Immirzi parameter for pure gravity is generalised to
the supergravity theories. Supergravity equations of motion are not modified by
such generalisations, thus preserving supersymmetry. Dependence on the Immirzi
parameter does not emerge in the classical equations of motion. This is in
contrast with the recent observation of Perez and Rovelli for gravity action
containing original Holst term and a minimally coupled Dirac fermion where the
classical equations of motion do develop a dependence on Immirzi parameter.Comment: 15 page
Logarithmic correction to the Bekenstein-Hawking entropy of the BTZ black hole
We derive an exact expression for the partition function of the Euclidean BTZ
black hole. Using this, we show that for a black hole with large horizon area,
the correction to the Bekenstein-Hawking entropy is , in
agreement with that for the Schwarzschild black hole obtained in the canonical
gravity formalism and also in a Lorentzian computation of BTZ black hole
entropy. We find that the right expression for the logarithmic correction in
the context of the BTZ black hole comes from the modular invariance associated
with the toral boundary of the black hole.Comment: LaTeX, 10 pages, typos corrected, clarifications adde
Using Incomplete Information for Complete Weight Annotation of Road Networks -- Extended Version
We are witnessing increasing interests in the effective use of road networks.
For example, to enable effective vehicle routing, weighted-graph models of
transportation networks are used, where the weight of an edge captures some
cost associated with traversing the edge, e.g., greenhouse gas (GHG) emissions
or travel time. It is a precondition to using a graph model for routing that
all edges have weights. Weights that capture travel times and GHG emissions can
be extracted from GPS trajectory data collected from the network. However, GPS
trajectory data typically lack the coverage needed to assign weights to all
edges. This paper formulates and addresses the problem of annotating all edges
in a road network with travel cost based weights from a set of trips in the
network that cover only a small fraction of the edges, each with an associated
ground-truth travel cost. A general framework is proposed to solve the problem.
Specifically, the problem is modeled as a regression problem and solved by
minimizing a judiciously designed objective function that takes into account
the topology of the road network. In particular, the use of weighted PageRank
values of edges is explored for assigning appropriate weights to all edges, and
the property of directional adjacency of edges is also taken into account to
assign weights. Empirical studies with weights capturing travel time and GHG
emissions on two road networks (Skagen, Denmark, and North Jutland, Denmark)
offer insight into the design properties of the proposed techniques and offer
evidence that the techniques are effective.Comment: This is an extended version of "Using Incomplete Information for
Complete Weight Annotation of Road Networks," which is accepted for
publication in IEEE TKD
Asymptotic Density of Open p-brane States with Zero-modes included
We obtain the asymptotic density of open p-brane states with zero-modes
included. The resulting logarithmic correction to the p-brane entropy has a
coefficient - \frac{p + 2}{2 p}, and is independent of the dimension of the
embedding spacetime. Such logarithmic corrections to the entropy, with
precisely this coefficient, appear in two other contexts also: a gas of
massless particles in p-dimensional space, and a Schwarzschild black hole in (p
+ 2)-dimensional anti de Sitter spacetime.Comment: 9 pages, Latex. V 2: Results are for open p-branes only; Title
modified; a few references and an acknowledgement adde
R\'enyi entanglement entropy of critical SU() spin chains
We present a study of the scaling behavior of the R\'{e}nyi entanglement
entropy (REE) in SU() spin chain Hamiltonians, in which all the spins
transform under the fundamental representation. These SU() spin chains are
known to be quantum critical and described by a well known Wess-Zumino-Witten
(WZW) non-linear sigma model in the continuum limit. Numerical results from our
lattice Hamiltonian are obtained using stochastic series expansion (SSE)
quantum Monte Carlo for both closed and open boundary conditions. As expected
for this 1D critical system, the REE shows a logarithmic dependence on the
subsystem size with a prefector given by the central charge of the SU() WZW
model. We study in detail the sub-leading oscillatory terms in the REE under
both periodic and open boundaries. Each oscillatory term is associated with a
WZW field and decays as a power law with an exponent proportional to the
scaling dimension of the corresponding field. We find that the use of periodic
boundaries (where oscillations are less prominent) allows for a better estimate
of the central charge, while using open boundaries allows for a better estimate
of the scaling dimensions. For completeness we also present numerical data on
the thermal R\'{e}nyi entropy which equally allows for extraction of the
central charge.Comment: 8 pages, 13 figure
Polymorphous low grade adenocarcinoma-an unusual presentation
Polymorphous low-grade adenocarcinoma (PLGA) is a neoplasm that occurs frequently in the mucosa of the soft and hard palates, in the buccal mucosa and in the upper lip and is very rare within the nasopharynx. We present a case of PLGA, which presented as a nasal polyp
Scaling in the Fan of an Unconventional Quantum Critical Point
We present results of extensive finite-temperature Quantum Monte Carlo
simulations on a SU(2) symmetric S=1/2 quantum antiferromagnet with a four-spin
interaction [Sandvik, Phys. Rev. Lett. 98, 227202 (2007)]. Our simulations,
which are free of the sign-problem and carried out on lattices containing in
excess of 1.6 X 10^4 spins, indicate that the four-spin interaction destroys
the N\'eel order at an unconventional z=1 quantum critical point, producing a
valence-bond solid paramagnet. Our results are consistent with the `deconfined
quantum criticality' scenario.Comment: published version, minor change
Dynamic elastic properties and magnetic susceptibility across the austenite-martensite transformation in site-disordered ferromagnetic Ni-Fe-Al alloy
Besides permitting an accurate determination of the
ferromagnetic-to-paramagnetic phase transition temperature and the
characteristic temperatures for the beginning and end of the growth of
martensite (austenite) phase at the expense of austenite (martensite) phase
while cooling (heating), the results of an extensive ac susceptibility, sound
velocity and internal friction investigation of the thermoelastic martensitic
transformation in melt-quenched (site-disordered) Ni55Fe20Al25 alloy provide a
clear experimental evidence for the following. Irreversible thermoelastic
changes (thermal hysteresis) occur in the austenite phase in the premartensitic
regime. In the heating cycle, the system retains the "memory" of the initiation
and subsequent growth of the martensitic phase (at the expense of the parent
austenite phase) that had taken place during the cooling cycle in the
austenite-martensite phase coexistence region. We report and discuss these
novel findings in this communication.Comment: 5 figure
Quantum phase transitions in bilayer SU(N) anti-ferromagnets
We present a detailed study of the destruction of SU(N) magnetic order in
square lattice bilayer anti-ferromagnets using unbiased quantum Monte Carlo
numerical simulations and field theoretic techniques. We study phase
transitions from an SU(N) N\'eel state into two distinct quantum disordered
"valence-bond" phases: a valence-bond liquid (VBL) with no broken symmetries
and a lattice-symmetry breaking valence-bond solid (VBS) state. For finite
inter-layer coupling, the cancellation of Berry phases between the layers has
dramatic consequences on the two phase transitions: the N\'eel-VBS transition
is first order for all accesible in our model, whereas the N\'eel-VBL
transition is continuous for N=2 and first order for N>= 4; for N=3 the
N\'eel-VBL transition show no signs of first-order behavior
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