372 research outputs found
Search for the Lepton Flavour Violating Higgs decay H --> tau mu at Hadron Colliders
We study the prospects to detect at hadron colliders the Lepton Flavour
Violating Higgs decay H --> tau mu, which can reach substantial branching
fractions in several extensions of the SM. Among them, the generic two higgs
doublet model can be taken as a representative case where B.R.(H --> tau mu)
can reach values of order 10^-1-10^-2. Bounds on the LFV factor kappa_{tau mu}
of order 0.8-1.7 can be derived at 95% c.l. at Tevatron Run-2 with 4 fb^-1 for
m_H = 110-150 GeV.Comment: 3 pages, 1 figure, uses RevTeX4. Contribution to Snowmass 200
Constraints on the parameters of the Left Right Mirror Model
We study some phenomenological constraints on the parameters of a left right
model with mirror fermions (LRMM) that solves the strong CP problem. In
particular, we evaluate the contribution of mirror neutrinos to the invisible Z
decay width (\Gamma_Z^{inv}), and we find that the present experimental value
on \Gamma_Z^{inv}, can be used to place an upper bound on the Z-Z' mixing angle
that is consistent with limits obtained previously from other low-energy
observables. In this model the charged fermions that correspond to the standard
model (SM) mix with its mirror counterparts. This mixing, simultaneously with
the Z-Z' one, leads to modifications of the \Gamma(Z --> f \bar{f}) decay
width. By comparing with LEP data, we obtain bounds on the standard-mirror
lepton mixing angles. We also find that the bottom quark mixing parameters can
be chosen to fit the experimental values of R_b, and the resulting values for
the Z-Z' mixing angle do not agree with previous bounds. However, this
disagreement disappears if one takes the more recent ALEPH data.Comment: 7 pages, 2 figures, REVTe
New Higgs signals induced by mirror fermion mixing effects
We study the conditions under which flavor violation arises in scalar-fermion
interactions, as a result of the mixing phenomena between the standard model
and exotic fermions. Phenomenological consequences are discussed within the
specific context of a left-right model where these additional fermions have
mirror properties under the new SU(2)_R gauge group.
Bounds on the parameters of the model are obtained from LFV processes; these
results are then used to study the LFV Higgs decays (H --> tau l_j, l_j = e,
mu), which reach branching ratios that could be detected at future colliders.Comment: 12 pages, 2 figures, ReVTex4, graphicx, to be published in Phys. Rev.
Lepton mass generation and family number violation mechanism in the model
Lepton family number violation processes arise in the model due to the presence of an extra neutral gauge boson, Z, with
family changing couplings, and due to the fact that this model demands the
existence of heavy exotic leptons. The mixing of the standard Z with Z and
the mixing of ordinary leptons with exotic ones induce together family changing
couplings on the Z and therefore nonvanishing rates for lepton family number
violation processes, such as , and . Additional contributions to the processes and
are induced from the mass generation mechanism. This last
type of contributions may compete with the above one, depending on the masses
of the scalars which participate in the diagrams which generate radiatively the
masses of the charged leptons. Using the experimental data we compute some
bounds for the mixings parameters and for the masses of the scalars.Comment: 12 pages, Latex, 7 figures. Accepted for publication in Int. Journ.
of Mod. Phys.
Lepton flavor violating Higgs boson decays from massive seesaw neutrinos
Lepton flavor violating Higgs boson decays are studied within the context of
seesaw models with Majorana massive neutrinos. Two models are considered: The
SM-seesaw, with the Standard Model Particle content plus three right handed
neutrinos, and the MSSM-seesaw, with the Minimal Supersymmetric Standard Model
particle content plus three right handed neutrinos and their supersymmetric
partners. The widths for these decays are derived from a full one-loop
diagrammatic computation in both models, and they are analyzed numerically in
terms of the seesaw parameters, namely, the Dirac and Majorana mass matrices.
Several possible scenarios for these mass matrices that are compatible with
neutrino data are considered. In the SM-seesaw case, very small branching
ratios are found for all studied scenarios. These ratios are explained as a
consequence of the decoupling behaviour of the heavy right handed neutrinos. In
contrast, in the MSSM-seesaw case, sizeable branching ratios are found for some
of the leptonic flavor violating decays of the MSSM neutral Higgs bosons and
for some choices of the seesaw matrices and MSSM parameters. The relevance of
the two competing sources of lepton flavor changing interactions in the
MSSM-seesaw case is also discussed. The non-decoupling behaviour of the
supersymmetric particles contributing in the loop-diagrams is finally shown.Comment: 44pgs. Version to appear in Phys.Rev.
Exact formulae for Higgs production through e gamma --> e H in the non-linear R_\xi gauge
We study the production of the SM Higgs boson (H^0) at future e gamma
colliders, through the reaction e gamma --> e H^0. The amplitude is evaluated
using the non-linear R_\xi gauge, which greatly simplifies the calculation.
Complete analytical expressions for the amplitudes are presented, which include
the contributions from 1-loop triangles "gamma gamma^* H^0" and "gamma Z^* H^0"
as well as the W- and Z-boxes with their related triangle graphs. The
resulting cross section for this mechanism indicates that it could be used to
detect the Higgs signal and to test its properties.Comment: 6 pages, 2 figures, RevTe
Production of neutral scalar Higgs bosons at colliders
We study the production of neutral scalar (CP even) Higgs bosons in the
process by including supersymmetric corrections to the
dominant -channel photon exchange amplitude. In addition to the standard
model and fermion loops, there are substantial contributions from
chargino loops. For some cases, these contributions can exceed those of the
's and ordinary fermions. The cross sections in this channel are generally
one or two orders of magnitude larger than those in the related channel
.Comment: 12 pages RevTeX, 5 postscript figures included, uses epsf.st
Bounding the Hubble flow in terms of the w parameter
The last decade has seen increasing efforts to circumscribe and bound the
cosmological Hubble flow in terms of model-independent constraints on the
cosmological fluid - such as, for instance, the classical energy conditions of
general relativity. Quite a bit can certainly be said in this regard, but much
more refined bounds can be obtained by placing more precise constraints (either
theoretical or observational) on the cosmological fluid. In particular, the use
of the w-parameter (w=p/rho) has become increasingly common as a surrogate for
trying to say something about the cosmological equation of state. Herein we
explore the extent to which a constraint on the w-parameter leads to useful and
nontrivial constraints on the Hubble flow, in terms of constraints on density
rho(z), Hubble parameter H(z), density parameter Omega(z), cosmological
distances d(z), and lookback time T(z). In contrast to other partial results in
the literature, we carry out the computations for arbitrary values of the space
curvature k in [-1,0,+1], equivalently for arbitrary Omega_0 <= 1.Comment: 15 page
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