3,131 research outputs found
Particle decay in false vacuum
We revisit the problem of decay of a metastable vacuum induced by the
presence of a particle. For the bosons of the `master field' the problem is
solved in any number of dimensions in terms of the spontaneous decay rate of
the false vacuum, while for a fermion we find a closed expression for the decay
rate in (1+1) dimensions. It is shown that in the (1+1) dimensional case an
infrared problem of one-loop correction to the decay rate of a boson is
resolved due to a cancellation between soft modes of the field. We also find
the boson decay rate in the `sine-Gordon staircase' model in the limits of
strong and weak coupling.Comment: 19 pages, 2 figure
Top quark longitudinal polarization near the threshold in l+ l- annihilation
We show that the longitudinal polarization of the top quarks produced in the
annihilation of e+ e- or mu+ mu- into tbar t at energies near the threshold is
not affected by the large Coulomb-type corrections, which greatly modify the
total cross section. Thus the longitudinal polarization, although small, may
provide an independent information on the mass and the width of the top quark,
largely independent of the uncertainty in alpha_s.Comment: 6 pages, LaTeX, no figures, added references, corrected typo
Degenerate Domain Wall Solutions in Supersymmetric Theories
A family of degenerate domain wall configurations, partially preserving
supersymmetry, is discussed in a generalized Wess-Zumino model with two scalar
superfields. We establish some general features inherent to the models with
continuously degenerate domain walls. For instance, for purely real
trajectories additional "integrals of motion" exist. The solution for the
profile of the scalar fields for any wall belonging to the family is found in
quadratures for arbitrary ratio of the coupling constants. For a special value
of this ratio the solution family is obtained explicitly in terms of elementary
functions. We also discuss the threshold amplitudes for multiparticle
production generated by these solutions. New unexpected nullifications of the
threshold amplitudes are found.Comment: 21 pages, LaTeX, 3 figures using epsf.st
Stochastic current switching in bistable resonant tunneling systems
Current-voltage characteristics of resonant-tunneling structures often
exhibit intrinsic bistabilities. In the bistable region of the I-V curve one of
the two current states is metastable. The system switches from the metastable
state to the stable one at a random moment in time. The mean switching time
\tau depends exponentially on the bias measured from the boundary of the
bistable region V_{th}. We find full expressions for \tau (including
prefactors) as functions of bias, sample geometry, and in-plane conductivity.
Our results take universal form upon appropriate renormalization of the
threshold voltage V_{th}. We also show that in large samples the switching
initiates inside, at the edge, or at a corner of the sample depending on the
parameters of the system.Comment: 21 pages, 5 figure
Decay of metastable current states in one-dimensional resonant tunneling devices
Current switching in a double-barrier resonant tunneling structure is studied
in the regime where the current-voltage characteristic exhibits intrinsic
bistability, so that in a certain range of bias two different steady states of
current are possible. Near the upper boundary V_{th} of the bistable region the
upper current state is metastable, and because of the shot noise it eventually
decays to the stable lower current state. We find the time of this switching
process in strip-shaped devices, with the width small compared to the length.
As the bias V is tuned away from the boundary value V_{th} of the bistable
region, the mean switching time \tau increases exponentially. We show that in
long strips \ln\tau \propto (V_{th} -V)^{5/4}, whereas in short strips \ln\tau
\propto (V_{th} -V)^{3/2}. The one-dimensional geometry of the problem enables
us to obtain analytically exact expressions for both the exponential and the
prefactor of \tau. Furthermore, we show that, depending on the parameters of
the system, the switching can be initiated either inside the strip, or at its
ends.Comment: 12 pages, 5 figures, update to published versio
Non-Abelian Dipole Radiation and the Heavy Quark Expansion
Dipole radiation in QCD is derived to the second order in . A
power-like evolution of the spin-singlet heavy quark operators is obtained to
the same accuracy. In particular, relation between a
short-distance low-scale running heavy quark mass and the \barMS mass is
given. We discuss the properties of the effective QCD coupling \aw(E) which
governs the dipole radiation. This coupling is advantageous for heavy quark
physics.Comment: 12 pages, Late
Neutrino electromagnetic properties and new bounds on neutrino magnetic moments
We give a brief outline of possible neutrino electromagnetic characteristics,
which can indicate new physics beyond the Standard Model. Special emphasis is
put on recent theoretical development in searches for neutrino magnetic
moments.Comment: 4 pages, to appear in J. Phys.: Conf. Ser. (2012), based on the talk
presented at the XII International Conference on Topics in Astroparticle and
Underground Physics (TAUP 2011), Munich 5-9 September 201
Heavy ion collisions: Correlations and Fluctuations in particle production
Correlations and fluctuations (the latter are directly related to the
2-particle correlations) is one of the important directions in analysis of
heavy ion collisions. At the current stage of RHIC exploration, when the
details matter, basically any physics question is addressed with help of
correlation techniques. In this talk I start with a general introduction to the
correlation and fluctuation formalism and discuss weak and strong sides of
different type of observables. In more detail, I discuss the two-particle
correlations/\mpt fluctuations. In spite of not observing any dramatic
changes in the event-by-event fluctuations with energy, which would indicate a
possible phase transition, such correlations measurements remain an interesting
and important subject, bringing valuable information. Lastly, I show how radial
flow can generate characteristic azimuthal, transverse momentum and rapidity
correlations, which could qualitatively explain many of recently observed
phenomena in nuclear collisions.Comment: 8 pages, 8 figures. Invited talk at 5th International Conference on
Physics and Astrophysics of Quark Gluon Plasma, February 8-12, 2005, Salt
Lake City, Kolkata, Indi
On the two-photon decay width of the sigma meson
We shortly report on the two-photon decay width of the light -meson
interpreted as a quarkonium state. Results are given in dependence on the
-mass and the constituent mass of the light quark. The triangle
quark-loop diagram, responsible for the two-photon transition, is carefully
evaluated: a term in the transition amplitude, often omitted in literature,
results in destructive interference with the leading term. As a result we show
that the two-photon decay width of the in the quarkonium picture is
less than 1 keV for the physical range of parameters.Comment: 6 pages, 4 figure
Dirac-Neutrino Magnetic Moment and the Dynamics of a Supernova Explosion
The double conversion of the neutrino helicity
has been analyzed for supernova conditions, where the first stage is due to the
interaction of the neutrino magnetic moment with plasma electrons and protons
in the supernova core, and the second stage, due to the resonance spin flip of
the neutrino in the magnetic field of the supernova envelope. It is shown that,
in the presence of the neutrino magnetic moment in the range and a magnetic field of G
between the neutrinosphere and the shock-stagnation region, an additional
energy of about erg, which is sufficient for a supernova explosion,
can be injected into this region during a typical shock-stagnation time.Comment: 10 pages, LaTeX, 4 EPS figures, accepted to JETP Letter
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