631 research outputs found
Particle Currents in a Space-Time dependent and CP-violating Higgs Background: a Field Theory Approach
Motivated by cosmological applications like electroweak baryogenesis, we
develop a field theoretic approach to the computation of particle currents on a
space-time dependent and CP-violating Higgs background. We consider the
Standard Model model with two Higgs doublets and CP violation in the scalar
sector, and compute both fermionic and Higgs currents by means of an expansion
in the background fields. We discuss the gauge dependence of the results and
the renormalization of the current operators, showing that in the limit of
local equilibrium, no extra renormalization conditions are needed in order to
specify the system completely.Comment: 21 pages, LaTeX file, uses epsf.sty. 4 figures available as a
compressed .ep
The role of the top mass in b-production at future lepton colliders
We compute the one loop contribution coming from vertex and box diagrams,
where virtual top quarks are exchanged, to the asymptotic energy behaviour of
pair production at future lepton colliders. We find that the effect
of the top mass is an extra linear logarithmic term of Sudakov type that is not
present in the case of (u,d,s,c) production. This appears to be particularly
relevant in the case of the cross section.Comment: 9 pages and 3 figures; version submitted to Phys.ReV.D,Rapid. e-mail:
[email protected]
Logarithmic expansion of electroweak corrections to four-fermion processes in the TeV region
Starting from a theoretical representation of the electroweak component of
four-fermion neutral current processes that uses as theoretical input the
experimental measurements at the Z peak, we consider the asymptotic high energy
behaviour in the Standard Model at one loop of those gauge-invariant
combinations of self-energies, vertices and boxes that contribute all the
different observables. We find that the logarithmic contribution due to the
renormalization group running of the various couplings is numerically
overwhelmed by single and double logarithmic terms of purely electroweak
(Sudakov-type) origin, whose separate relative effects grow with energy,
reaching the 10% size at about one TeV. We then propose a simple "effective"
parametrization that aims at describing the various observables in the TeV
region, and discuss its validity both beyond and below 1 TeV, in particular in
the expected energy range of future linear electron-positron (LC) and muon-muon
colliders.Comment: 23 pages and 9 figures; version submitted to Phys.Rev.D. e-mail:
[email protected]
Towards a Nonequilibrium Quantum Field Theory Approach to Electroweak Baryogenesis
We propose a general method to compute -violating observables from
extensions of the standard model in the context of electroweak baryogenesis. It
is alternative to the one recently developed by Huet and Nelson and relies on a
nonequilibrium quantum field theory approach. The method is valid for all
shapes and sizes of the bubble wall expanding in the thermal bath during a
first-order electroweak phase transition. The quantum physics of -violation
and its suppression coming from the incoherent nature of thermal processes are
also made explicit.Comment: 19 pages, 1 figure available upon e-mail reques
Initial State Radiation in Majorana Dark Matter Annihilations
The cross section for a Majorana Dark Matter particle annihilating into light
fermions is helicity suppressed. We show that, if the Dark Matter is the
neutral Majorana component of a multiplet which is charged under the
electroweak interactions of the Standard Model, the emission of gauge bosons
from the initial state lifts the suppression and allows an s-wave annihilation.
The resulting energy spectra of stable Standard Model particles are importantly
affected. This has an impact on indirect searches for Dark Matter.Comment: 9 pages, 3 figure
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