2,153 research outputs found
Mixing Renormalization for Scalar Fields
We consider the renormalization of theories with many scalar fields. We
discuss at the one-loop level some simple, non-gauge models with an arbitrary
number of scalars and fermions both in mass-shell and MS schemes. In MS scheme
we give a detailed qualitative analysis of the RG flow of dimensionless
couplings in flavor space.Comment: 32 pages, LaTeX2e, AmsLaTeX, minor typos correcte
Can the string scale be related to the cosmic baryon asymmetry?
In a previous work, a mechanism was presented by which baryon asymmetry can
be generated during inflation from elliptically polarized gravitons.
Nonetheless, the mechanism only generated a realistic baryon asymmetry under
special circumstances which requires an enhancement of the lepton number from
an unspecified GUT. In this note we provide a stringy embedding of this
mechanism through the Green-Schwarz mechanism, demonstrating that if the
model-independent axion is the source of the gravitational waves responsible
for the lepton asymmetry, one can observationally constrain the string scale
and coupling.Comment: 12 Pages, typo corrected in the tex
Master equation approach to friction at the mesoscale
At the mesoscale friction occurs through the breaking and formation of local
contacts. This is often described by the earthquake-like model which requires
numerical studies. We show that this phenomenon can also be described by a
master equation, which can be solved analytically in some cases and provides an
efficient numerical solution for more general cases. We examine the effect of
temperature and aging of the contacts and discuss the statistical properties of
the contacts for different situations of friction and their implications,
particularly regarding the existence of stick-slip.Comment: To be published in Physical Review
V,W and X in Technicolour Models
Light techni-fermions and pseudo Goldstone bosons that contribute to the
electroweak radiative correction parameters V,W and X may relax the constraints
on technicolour models from the experimental values of the parameters S and T.
Order of magnitude estimates of the contributions to V,W and X from light
techni-leptons are made when the the techni-neutrino has a small Dirac mass or
a large Majorana mass. The contributions to V,W and X from pseudo Goldstone
bosons are calculated in a gauged chiral Lagrangian. Estimates of V,W and X in
one family technicolour models suggest that the upper bounds on S and T should
be relaxed by between 0.1 and 1 depending upon the precise particle spectrum.Comment: 19 pages + 2 pages of ps figs, SWAT/1
Energy Anomaly and Polarizability of Carbon Nanotubes
The energy of electron Fermi sea perturbed by external potential, represented
as energy anomaly which accounts for the contribution of the deep-lying states,
is analyzed for massive d = 1+1 Dirac fermions on a circle. The anomaly is a
universal function of the applied field, and is related to known
field-theoretic anomalies. We express transverse polarizability of Carbon
nanotubes via the anomaly, in a way which exhibits the universality and
scale-invariance of the response dominated by pi-electrons and qualitatively
different from that of dielectric and conducting shells. Electron band
transformation in a strong-field effect regime is predicted.Comment: 4 pg
Hydrogen Atom in Relativistic Motion
The Lorentz contraction of bound states in field theory is often appealed to
in qualitative descriptions of high energy particle collisions. Surprisingly,
the contraction has not been demonstrated explicitly even in simple cases such
as the hydrogen atom. It requires a calculation of wave functions evaluated at
equal (ordinary) time for bound states in motion. Such wave functions are not
obtained by kinematic boosts from the rest frame. Starting from the exact
Bethe-Salpeter equation we derive the equal-time wave function of a
fermion-antifermion bound state in QED, i.e., positronium or the hydrogen atom,
in any frame to leading order in alpha. We show explicitly that the bound state
energy transforms as the fourth component of a vector and that the wave
function of the fermion-antifermion Fock state contracts as expected.
Transverse photon exchange contributes at leading order to the binding energy
of the bound state in motion. We study the general features of the
corresponding fermion-antifermion-photon Fock states, and show that they do not
transform by simply contracting. We verify that the wave function reduces to
the light-front one in the infinite momentum frame.Comment: 20 pages, 10 figures; v2: some changes in discussion, accepted for
publication in Phys.Rev.
Properties of a Discrete Quantum Field Theory
A scalar quantum field theory defined on a discrete spatial coordinate is
examined. The renormalization of the lattice propagator is discussed with an
emphasis on the periodic nature of the associated momentum coordinate. The
analytic properties of the scattering amplitudes indicate the development of a
second branch point on which the branch cut from the optical theorem
terminates.Comment: 7 pages, 1 figur
Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential
We consider QED in five dimensions in a configuration where matter is
localized on a 3-brane while foton propagates in the bulk. The idea is to
investigate the effects of the Kaluza-Klein modes of the photon in the
relativistic regime, but in low energy, and in the nonrelativistic regime. In
the relativistic regime, we calculate the cross section for the reaction . We compare our theoretical result with a precise
measurement of this cross section at GeV. As result, we
extract a lower bound on the size of the extra dimension. In the
nonrelativistic regime, we derive the contribution for the Coulomb potential
due to the whole tower of the Kaluza-Klein excited modes of the photon. We use
the modified potential to calculate the Rutherford scattering differential
cross section.Comment: minor changes, three new refs. added, to appear in IJMP
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