24,700 research outputs found
Classical Non-Abelian Solitons
In two space-time dimensions a class of classical multicomponent scalar field
theories with discrete, in general non-Abelian global symmetry is considered.
The corresponding soliton solutions are given for the cases of 2, 3, and 4
components.Comment: 5 pages, KL-TH-94/2
Spectral correlations in the crossover between GUE and Poisson regularity: on the identification of scales
Motivated by questions of present interest in nuclear and condensed matter
physics we consider the superposition of a diagonal matrix with independent
random entries and a GUE. The relative strength of the two contributions is
determined by a parameter suitably defined on the unfolded scale.
Using results for the spectral two-point correlator of this model obtained in
the framework of the supersymmetry method we focus attention on two different
regimes. For << 1 the correlations are given by Dawson's integral
while for >> 1 we derive a novel analytical formula for the two-point
function. In both cases the energy scales, in units of the mean level spacing,
at which deviations from pure GUE behavior become noticable can be identified.
We also derive an exact expansion of the local level density for finite level
number.Comment: 15 pages, Revtex, no figures, to be published in special issue of J.
Math. Phys. (1997
Future dynamics in f(R) theories
The gravity theories provide an alternative way to explain the current
cosmic acceleration without invoking dark energy matter component. However, the
freedom in the choice of the functional forms of gives rise to the
problem of how to constrain and break the degeneracy among these gravity
theories on theoretical and/or observational grounds. In this paper to proceed
further with the investigation on the potentialities, difficulties and
limitations of gravity, we examine the question as to whether the future
dynamics can be used to break the degeneracy between gravity theories by
investigating the future dynamics of spatially homogeneous and isotropic dust
flat models in two gravity theories, namely the well known gravity and another by A. Aviles et al., whose motivation comes
from the cosmographic approach to gravity. To this end we perform a
detailed numerical study of the future dynamic of these flat model in these
theories taking into account the recent constraints on the cosmological
parameters made by the Planck team. We show that besides being powerful for
discriminating between gravity theories, the future dynamics technique
can also be used to determine the fate of the Universe in the framework of
these gravity theories. Moreover, there emerges from our numerical
analysis that if we do not invoke a dark energy component with
equation-of-state parameter one still has dust flat FLRW solution
with a big rip, if gravity deviates from general relativity via . We also show that FLRW dust solutions with do not
necessarily lead to singularity.Comment: 12 pages, 8 figures. V2: Generality and implications of the results
are emphasized, connection with the recent literature improved, typos
corrected, references adde
The Standard Quantum Limit of Coherent Beam Combining
Coherent beam combining refers to the process of generating a bright output
beam by merging independent input beams with locked relative phases. We report
the first quantum mechanical noise limit calculations for coherent beam
combining and compare our results to quantum-limited amplification. Our
coherent beam combining scheme is based on an optical Fourier transformation
which renders the scheme compatible with integrated optics. The scheme can be
layed out for an arbitrary number of input beams and approaches the shot noise
limit for a large number of inputs
Systematic Mapping of the Hubbard Model to the Generalized t-J Model
The generalized t-J model conserving the number of double occupancies is
constructed from the Hubbard model at and in the vicinity of half-filling at
strong coupling. The construction is realized by a self-similar continuous
unitary transformation. The flow equation is closed by a truncation scheme
based on the spatial range of processes. We analyze the conditions under which
the t-J model can be set up and we find that it can only be defined for
sufficiently large interaction. There, the parameters of the effective model
are determined.Comment: 16 pages, 13 figures included. v2: Order of sections changed.
Calculation and discussion of apparent gap in Section IV.A correcte
Treponema denticola in Disseminating Endodontic Infections
Treponema denticola is a consensus periodontal pathogen that has recently been associated with endodontic pathology. In this study, the effect of mono-infection of the dental pulp with T. denticola and with polymicrobial “red-complex” organisms (RC) (Porphyromonas gingivalis, Tannerella forsythia, and T. denticola) in inducing disseminating infections in wild-type (WT) and severe-combined-immunodeficiency (SCID) mice was analyzed. After 21 days, a high incidence (5/10) of orofacial abscesses was observed in SCID mice mono-infected with T. denticola, whereas abscesses were rare in SCID mice infected with the red-complex organisms or in wildtype mice. Splenomegaly was present in all groups, but only mono-infected SCID mice had weight loss. T. denticola DNA was detected in the spleen, heart, and brain of mono-infected SCID mice and in the spleen from mono-infected wild-type mice, which also had more periapical bone resorption. The results indicate that T. denticola has high pathogenicity, including dissemination to distant organs, further substantiating its potential importance in oral and linked systemic conditions
Generalized Parton Distributions of ^3He
A realistic microscopic calculation of the unpolarized quark Generalized
Parton Distribution (GPD) of the nucleus is presented. In
Impulse Approximation, is obtained as a convolution between the GPD of
the internal nucleon and the non-diagonal spectral function, describing
properly Fermi motion and binding effects. The proposed scheme is valid at low
values of , the momentum transfer to the target, the most relevant
kinematical region for the coherent channel of hard exclusive processes. The
obtained formula has the correct forward limit, corresponding to the standard
deep inelastic nuclear parton distributions, and first moment, giving the
charge form factor of . Nuclear effects, evaluated by a modern realistic
potential, are found to be larger than in the forward case. In particular, they
increase with increasing the momentum transfer when the asymmetry of the
process is kept fixed, and they increase with the asymmetry at fixed momentum
transfer. Another relevant feature of the obtained results is that the nuclear
GPD cannot be factorized into a -dependent and a
-independent term, as suggested in prescriptions proposed for finite
nuclei. The size of nuclear effects reaches 8 % even in the most important part
of the kinematical range under scrutiny. The relevance of the obtained results
to study the feasibility of experiments is addressed.Comment: 23 pages, 8 figures; Discussion in section II enlarged; discussion in
section IV shortened. Final version accepted by Phys. Rev.
A Gauge-fixed Hamiltonian for Lattice QCD
We study the gauge fixing of lattice QCD in 2+1 dimensions, in the
Hamiltonian formulation. The technique easily generalizes to other theories and
dimensions. The Hamiltonian is rewritten in terms of variables which are gauge
invariant except under a single global transformation. This paper extends
previous work, involving only pure gauge theories, to include matter fields.Comment: 7 pages of LaTeX, RU-92-45 and BUHEP-92-3
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