37,663 research outputs found
Radiative Electroweak Symmetry-Breaking Revisited
In the absence of a tree-level scalar-field mass, renormalization-group
methods permit the explicit summation of leading-logarithm contributions to all
orders of the perturbative series within the effective potential for
electroweak symmetry. This improvement of the effective
potential function is seen to reduce residual dependence on the renormalization
mass scale. The all-orders summation of leading logarithm terms involving the
dominant three couplings contributing to radiative corrections is suggestive of
a potential characterized by a plausible Higgs boson mass of 216 GeV. However,
the tree potential's local minimum at is restored if QCD is
sufficiently strong.Comment: revtex, 4 pages, 1 eps figure embedded in manuscript. Updated version
contains additional comments and corrects minor error
Dark energy from conformal symmetry breaking
The breakdown of conformal symmetry in a conformally invariant scalar-tensor
gravitational model is revisited in the cosmological context. Although the old
scenario of conformal symmetry breaking in cosmology containing scalar field
has already been used in many earlier works, it seems that no special attention
has been paid for the investigation on the possible connection between the
breakdown of conformal symmetry and the existence of dark energy. In this
paper, it is shown that the old scenario of conformal symmetry breaking in
cosmology, if properly interpreted, not only has a potential ability to
describe the origin of dark energy as a symmetry breaking effect, but also may
resolve the coincidence problem.Comment: 11 pages, minor revision, published online in EPJ
Charge symmetry breaking in hypernuclei revisited
The large charge symmetry breaking (CSB) implied by the binding
energy difference He)H) = 0.350.06 MeV
of the mirror hypernuclei ground states, determined from emulsion
studies, has defied theoretical attempts to reproduce it in terms of CSB in
hyperon masses and in hyperon-nucleon interactions, including one pion exchange
arising from mixing. Using a schematic strong-interaction
coupling model developed by Akaishi and
collaborators for -shell hypernuclei, we revisit the evaluation of
CSB in the hypernuclei and extend it to -shell mirror
hypernuclei. The model yields values of MeV. Smaller size and mostly negative -shell
binding energy differences are calculated for the mirror hypernuclei,
in rough agreement with the few available data. CSB is found to reduce by
almost 30 keV the 110 keV B g.s. doublet splitting
anticipated from the hyperon-nucleon strong-interaction spin dependence,
thereby explaining the persistent experimental failure to observe the -ray transition.Comment: a few clarifying statements added to v2; matches published PLB
version plus a note added after publication on p.1
Chiral symmetry breaking with no bilinear condensate revisited
While chiral symmetry breaking in the QCD vacuum is attributed to nonzero
chiral condensate, an alternative symmetry breaking pattern with no chiral
condensate is also possible, as pointed out by Stern. This hypothetical phase
was excluded in QCD at zero density long time ago, but nothing forbids it at
finite baryon density. In this work, we study the dependence of this
unorthodox phase on the basis of chiral perturbation theory. Physical
observables such as energy density, topological susceptibility, non-local
chiral order parameter and meson masses are computed analytically in the
epsilon-regime. At nonzero we find an exotic phase that breaks
vectorial flavor symmetries in a way analogous to the Aoki phase in lattice
QCD.Comment: 27 pages, 8 figures. v2: minor revisions, published versio
Chiral symmetry breaking revisited: the gap equation with lattice ingredients
We study chiral symmetry breaking in QCD, using as ingredients in the quark
gap equation recent lattice results for the gluon and ghost propagators. The
Ansatz employed for the quark-gluon vertex is purely non-Abelian, introducing a
crucial dependence on the ghost dressing function and the quark-ghost
scattering amplitude. The numerical impact of these quantities is considerable:
the need to invoke confinement explicitly is avoided, and the dynamical quark
masses generated are of the order of 300 MeV. In addition, the pion decay
constant and the quark condensate are computed, and are found to be in good
agreement with phenomenology.Comment: 3 pages, 5 figures. Talk presented at the Quark Confinement and the
Hadron Spectrum - Madrid 2010, August 30th - September 3rd 2010, Madrid,
Spai
Parisi Phase in a Neuron
Pattern storage by a single neuron is revisited. Generalizing Parisi's
framework for spin glasses we obtain a variational free energy functional for
the neuron. The solution is demonstrated at high temperature and large relative
number of examples, where several phases are identified by thermodynamical
stability analysis, two of them exhibiting spontaneous full replica symmetry
breaking. We give analytically the curved segments of the order parameter
function and in representative cases compute the free energy, the storage
error, and the entropy.Comment: 4 pages in prl twocolumn format + 3 Postscript figures. Submitted to
Physical Review Letter
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