4,899 research outputs found
Non-Equilibrium Time Evolution in Quantum Field Theory
The time development of equal-time correlation functions in quantum mechanics
and quantum field theory is described by an exact evolution equation for
generating functionals. This permits a comparison between classical and quantum
evolution in non-equilibrium systems.Comment: 7 pages, LaTe
An algorithm for the solution of the distribution problem of probabilistic linear programming /
External Momentum, Volume Effects, and the Nucleon Magnetic Moment
We analyze the determination of volume effects for correlation functions that
depend on an external momentum. As a specific example, we consider finite
volume nucleon current correlators, and focus on the nucleon magnetic moment.
Because the multipole decomposition relies on SO(3) rotational invariance, the
structure of such finite volume corrections is unrelated to infinite volume
multipole form factors. One can deduce volume corrections to the magnetic
moment only when a zero-mode photon coupling vanishes, as occurs at
next-to-leading order in heavy baryon chiral perturbation theory. To deduce
such finite volume corrections, however, one must assume continuous momentum
transfer. In practice, volume corrections with momentum transfer dependence are
required to address the extraction of the magnetic moment, or other observables
that arise in momentum dependent correlation functions. Additionally we shed
some light on a puzzle concerning differences in lattice form factor data at
equal values of momentum transfer squared.Comment: 21 pages, 5 figures; discussion in Sect. IV C expanded, Figs. now B&W
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Surface Brightness and Stellar Populations at the Outer Edge of the Large Magellanic Cloud: No Stellar Halo Yet
We present a high quality CMD for a 36'x 36' field located 8 degrees (7 kpc)
from the LMC center, as well as a precise determination of the LMC surface
brightness derived from the resolved stellar population out to this large
galactocentric radius. This deep CMD shows for the first time the detailed age
distribution at this position, where the surface brightness is V=26.5 mag/sq".
At a radius R=474' the main sequence is well populated from the oldest turnoff
at I=21.5 to the 2.5 Gyr turnoff at I=19.5. Beyond this radius, a relatively
strong gradient in the density of stars with ages in the 2.5-4 Gyr range is
apparent. There are some stars brighter and bluer than the main population,
quite uniformly distributed over the whole area surveyed, which are well
matched by a 1.5 Gyr isochrone and may be indicative of a relatively recent
star formation, or merger, event. The surface brightness profile of the LMC
remains exponential to this large galactocentric radius and shows no evidence
of disk truncation. Combining the information on surface brightness and stellar
population we conclude that the LMC disk extends (and dominates over a possible
stellar halo) out to a distance of at least 7 kpc. These results confirm that
the absence of blue stars in the relatively shallow off-center CMDs of dIrr
galaxies is not necessarily evidence for an exclusively old stellar population
resembling the halo of the Milky Way.Comment: ApJLett, in press 13 pages including 3 color figure
Dynamic critical behaviour in Ising spin glasses
The critical dynamics of Ising spin glasses with Bimodal, Gaussian, and
Laplacian interaction distributions are studied numerically in dimensions 3 and
4. The data demonstrate that in both dimensions the critical dynamic exponent
, the non-equilibrium autocorrelation decay exponent
, and the critical fluctuation-dissipation ratio
all vary strongly and systematically with the form of the
interaction distribution.Comment: 8 pages, 4 figures, version to appear in Phys. Rev.
Quantum Isometrodynamics
Classical Isometrodynamics is quantized in the Euclidean plus axial gauge.
The quantization is then generalized to a broad class of gauges and the
generating functional for the Green functions of Quantum Isometrodynamics (QID)
is derived. Feynman rules in covariant Euclidean gauges are determined and QID
is shown to be renormalizable by power counting. Asymptotic states are
discussed and new quantum numbers related to the "inner" degrees of freedom
introduced. The one-loop effective action in a Euclidean background gauge is
formally calculated and shown to be finite and gauge-invariant after
renormalization and a consistent definition of the arising "inner" space
momentum integrals. Pure QID is shown to be asymptotically free for all
dimensions of "inner" space whereas QID coupled to the Standard Model
fields is not asymptotically free for D <= 7. Finally nilpotent BRST
transformations for Isometrodynamics are derived along with the BRST symmetry
of the theory and a scetch of the general proof of renormalizability for QID is
given.Comment: 38 page
Many-body physics in the radio frequency spectrum of lattice bosons
We calculate the radio-frequency spectrum of a trapped cloud of cold bosonic
atoms in an optical lattice. Using random phase and local density
approximations we produce both trap averaged and spatially resolved spectra,
identifying simple features in the spectra that reveal information about both
superfluidity and correlations. Our approach is exact in the deep Mott limit
and in the deep superfluid when the hopping rates for the two internal spin
states are equal. It contains final state interactions, obeys the Ward
identities (and the associated conservation laws), and satisfies the -sum
rule. Motivated by earlier work by Sun, Lannert, and Vishveshwara [Phys. Rev. A
\textbf{79}, 043422 (2009)], we also discuss the features which arise in a
spin-dependent optical lattice.Comment: 6 pages, 4 figures, 13 subfigure
Heavy Fermion Quantum Criticality
During the last few years, investigations of Rare-Earth materials have made
clear that not only the heavy fermion phase in these systems provides
interesting physics, but the quantum criticality where such a phase dies
exhibits novel phase transition physics not fully understood. Moreover,
attempts to study the critical point numerically face the infamous fermion sign
problem, which limits their accuracy. Effective action techniques and
Callan-Symanzik equations have been very popular in high energy physics, where
they enjoy a good record of success. Yet, they have been little exploited for
fermionic systems in condensed matter physics. In this work, we apply the RG
effective action and Callan-Symanzik techiques to the heavy fermion problem. We
write for the first time the effective action describing the low energy physics
of the system. The f-fermions are replaced by a dynamical scalar field whose
nonzero expected value corresponds to the heavy fermion phase. This removes the
fermion sign problem, making the effective action amenable to numerical studies
as the effective theory is bosonic. Renormalization group studies of the
effective action can be performed to extract approximations to nonperturbative
effects at the transition. By performing one-loop renormalizations, resummed
via Callan-Symanzik methods, we describe the heavy fermion criticality and
predict the heavy fermion critical dynamical susceptibility and critical
specific heat. The specific heat coefficient exponent we obtain (0.39) is in
excellent agreement with the experimental result at low temperatures (0.4).Comment: 5 pages. In the replacement, the numerical value for the specific
heat coefficient exponent has been included explicitly in decimal form, and
has been compared with the experimental result
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