807 research outputs found
New limits on the mass of neutral Higgses in General Models
In general electroweak models with weakly coupled (and otherwise arbitrary)
Higgs sector there always exists in the spectrum a scalar state with mass
controlled by the electroweak scale. A new and simple recipe to compute an
analytical tree-level upper bound on the mass of this light scalar is given. We
compare this new bound with similar ones existing in the literature and show
how to extract extra information on heavier neutral scalars in the spectrum
from the interplay of independent bounds. Production of these states at future
colliders is addressed and the implications for the decoupling limit in which
only one Higgs is expected to remain light are discussed.Comment: 14 pages, LaTe
A Way to Dynamically Overcome the Cosmological Constant Problem
The Cosmological Constant problem can be solved once we require that the full
standard Einstein Hilbert lagrangian, gravity plus matter, is multiplied by a
total derivative. We analyze such a picture writing the total derivative as the
covariant gradient of a new vector field (b_mu). The dynamics of this b_mu
field can play a key role in the explanation of the present cosmological
acceleration of the Universe.Comment: 5 page
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
Exploding Sudakov form factors
Contrary to what naively expected, we find that in spontaneously broken gauge theories the resummations of Sudakov double logs (in the presence of an energy scale Q much larger than the mass scale v of the spontaneous gauge
breaking) are exponentiated also with a positive coefficient e+α log2 Q2v2. The amplitudes affected by such a term are proportional to v and have a non-zero total
gauge charge. As a working example we consider a model with two Abelian gauge groups U'(1)⊗U(1) with large mass splitting MZ' >>� �MZ, and we compute leading radiative corrections to the decay of the heavy extra Z' boson into light fermions
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
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
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