1,538 research outputs found
A Heavy Fermion Can Create a Soliton: A 1+1 Dimensional Example
We show that quantum effects can stabilize a soliton in a model with no
soliton at the classical level. The model has a scalar field chirally coupled
to a fermion in 1+1 dimensions. We use a formalism that allows us to calculate
the exact one loop fermion contribution to the effective energy for a spatially
varying scalar background. This energy includes the contribution from
counterterms fixed in the perturbative sector of the theory. The resulting
energy is therefore finite and unambiguous. A variational search then yields a
fermion number one configuration whose energy is below that of a single free
fermion.Comment: 10 pages, RevTeX, 2 figures composed from 4 .eps files; v2: fixed
minor errors, added reference; v3: corrected reference added in v
Light Scalar Mesons as Manifestation of Spontaneously Broken Chiral Symmetry
Attention is paid to the production mechanisms of light scalars that reveal
their nature. We reveal the chiral shielding of the \sigma(600) meson. We show
that the kaon loop mechanism of the \phi radiative decays, ratified by
experiment, points to the four-quark nature of light scalars. We show also that
the light scalars are produced in the two photon collisions via four-quark
transitions in contrast to the classic P wave tensor q\bar q mesons that are
produced via two-quark transitions . The history of
spontaneous breaking of symmetry in quantum physics is discussed in Appendix.Comment: Talk at The International Bogolyubov Conference "Problems of
Theoretical and Mathematical Physics" devoted to the 100th anniversary of
N.N.Bogolyubov's birth that was held from August 21 to August 22,2009 in
Moscow at the Russian Academy of Sciences (RAS) and from August 23 to August
27, 2009 in Dubna at the Joint Institute for Nuclear Research (JINR
Neutrino scattering off pair-breaking and collective excitations in superfluid neutron matter and in color-flavor locked quark matter
We calculate the correlation functions needed to describe the linear response
of superfluid matter, and go on to calculate the differential cross section for
neutral-current neutrino scattering in superfluid neutron matter and in
color-flavor locked quark matter (CFL). We report the first calculation of
scattering rates that includes neutrino interactions with both pair-breaking
excitations and low-lying collective excitations (Goldstone modes). Our results
apply both above and below the critical temperature, allowing use in
simulations of neutrino transport in supernovae and neutron stars.Comment: 22 pages, 9 figure
Hartree-Fock and Many-Body Perturbation Theory with Correlated Realistic NN-Interactions
We employ correlated realistic nucleon-nucleon interactions for the
description of nuclear ground states throughout the nuclear chart within the
Hartree-Fock approximation. The crucial short-range central and tensor
correlations, which are induced by the realistic interaction and cannot be
described by the Hartree-Fock many-body state itself, are included explicitly
by a state-independent unitary transformation in the framework of the unitary
correlation operator method (UCOM). Using the correlated realistic interaction
V_UCOM resulting from the Argonne V18 potential, bound nuclei are obtained
already on the Hartree-Fock level. However, the binding energies are smaller
than the experimental values because long-range correlations have not been
accounted for. Their inclusion by means of many-body perturbation theory leads
to a remarkable agreement with experimental binding energies over the whole
mass range from He-4 to Pb-208, even far off the valley of stability. The
observed perturbative character of the residual long-range correlations and the
apparently small net effect of three-body forces provides promising
perspectives for a unified nuclear structure description.Comment: 14 pages, 8 figures, 3 tables, using REVTEX
Cloning a new cytochrome P450 isoform (CYP356A1) from oyster Crassostrea gigas
Author Posting. © Elsevier B.V., 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Environmental Research 66 (2008): 15-18, doi:10.1016/j.marenvres.2008.02.010.We have cloned the full-length cDNA of the first member of a new cytochrome P450
(CYP) family from the Pacific oyster Crassostrea gigas. This new CYP gene was obtained
based on an initial 331 bp fragment previously identified among the list of the differentially
expressed genes in oysters exposed to untreated domestic sewage. The full-length CYP has
an open reading frame of 1500 bp and based on its deduced aminoacid sequence was
classified as a member of a new subfamily, CYP356A1. A phylogenetic analysis showed
that CYP356A1 is closely related to members of the CYP17 and CYP1 subfamilies. Semiquantitative
RT-PCR was performed to analyze the CYP356A1 expression in different
tissues of the oyster (digestive gland, gill, mantle and adductor muscle). Results showed
slightly higher CYP356A1 expression in digestive gland and mantle, than the other tissues,
indicating a possible role of the CYP356A1 in the xenobiotic biotransformation and/or
steroid metabolism.This work was supported by CNPq-Universal to ACDB. ACDB is recipient of Productivity
Fellowship from CNPq
Study of the ground-state energy of 40Ca with the CD-Bonn nucleon-nucleon potential
We have calculated the ground-state energy of the doubly-magic nucleus 40Ca
within the framework of the Goldstone expansion using the CD-Bonn
nucleon-nucleon potential. The short-range repulsion of this potential has been
renormalized by integrating out its high-momentum components so as to derive a
low-momentum potential V-low-k defined up to a cutoff momentum Lambda. A simple
criterion has been employed to establish a connection between this cutoff
momentum and the size of the two-nucleon model space in the harmonic oscillator
basis. This model-space truncation approach provides a reliable way to
renormalize the free nucleon-nucleon potential preserving its many-body
physics. The role of the 3p-3h and 4p-4h excitations in the description of the
ground state of 40Ca is discussed.Comment: 4 pages, 1 figure, 1 table, to be published in Physical Review
Fractional and Integer Charges from Levinson's Theorem
We compute fractional and integer fermion quantum numbers of static
background field configurations using phase shifts and Levinson's theorem. By
extending fermionic scattering theory to arbitrary dimensions, we implement
dimensional regularization in a 1+1 dimensional gauge theory. We demonstrate
that this regularization procedure automatically eliminates the anomaly in the
vector current that a naive regulator would produce. We also apply these
techniques to bag models in one and three dimensions.Comment: 16 pages, uses RevTex, 1 figure; v2: minor correction
Nuclear Structure Calculations with Low-Momentum Potentials in a Model Space Truncation Approach
We have calculated the ground-state energy of the doubly magic nuclei 4He,
16O and 40Ca within the framework of the Goldstone expansion starting from
various modern nucleon-nucleon potentials. The short-range repulsion of these
potentials has been renormalized by constructing a low-momentum potential
V-low-k. We have studied the connection between the cutoff momemtum Lambda and
the size of the harmonic oscillator space employed in the calculations. We have
found a fast convergence of the results with a limited number of oscillator
quanta.Comment: 6 pages, 8 figures, to be published on Physical Review
Brueckner-Goldstone perturbation theory for the half-filled Hubbard model in infinite dimensions
We use Brueckner-Goldstone perturbation theory to calculate the ground-state
energy of the half-filled Hubbard model in infinite dimensions up to fourth
order in the Hubbard interaction. We obtain the momentum distribution as a
functional derivative of the ground-state energy with respect to the bare
dispersion relation. The resulting expressions agree with those from
Rayleigh-Schroedinger perturbation theory. Our results for the momentum
distribution and the quasi-particle weight agree very well with those obtained
earlier from Feynman-Dyson perturbation theory for the single-particle
self-energy. We give the correct fourth-order coefficient in the ground-state
energy which was not calculated accurately enough from Feynman-Dyson theory due
to the insufficient accuracy of the data for the self-energy, and find a good
agreement with recent estimates from Quantum Monte-Carlo calculations.Comment: 15 pages, 8 fugures, submitted to JSTA
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