1,220 research outputs found
FRW Cosmological Perturbations in Massive Bigravity
Cosmological perturbations of FRW solutions in ghost free massive bigravity,
including also a second matter sector, are studied in detail. At early time, we
find that sub horizon exponential instabilities are unavoidable and they lead
to a premature departure from the perturbative regime of cosmological
perturbations.Comment: latex, 14 page
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]
Spherically Symmetric Solutions in Ghost-Free Massive Gravity
Recently, a class of theories of massive gravity has been shown to be
ghost-free. We study the spherically symmetric solutions in the bigravity
formulation of such theories. In general, the solutions admit both a Lorentz
invariant and a Lorentz breaking asymptotically flat behaviour and also fall in
two branches. In the first branch, all solutions can be found analitycally and
are Schwarzschild-like, with no modification as is found for other classes of
theories. In the second branch, exact solutions are hard to find, and relying
on perturbation theory, Yukawa-like modifications of the static potential are
found. The general structure of the solutions suggests that the bigravity
formulation of massive gravity is crucial and more than a tool.Comment: 15 pages. Some change in the reference
Particle Currents on a CP Violating Higgs Background and the Spontaneous Baryogenesis Mechanism
We compute the particle currents induced on a bubble wall background at
finite temperature in a model with CP violation in the Higgs sector. Using a
field theory approach we show that fermionic currents arise at one loop, so
that a suppression factor with respect to previous
computations is found. The contributions to the Higgs currents are also derived
and their relevancy for the spontaneous baryogenesis mechanism is discussed.Comment: 10 pages, LaTeX file, uses epsf.sty, 4 figures available as a
compressed .eps fil
- …