976 research outputs found
Full O(alpha) corrections to e+e- -> sf_i sf_j
We present a complete precision analysis of the sfermion pair production
process e+e- -> sf_i sf_j (f = t, b, tau, nu_tau) in the Minimal Supersymmetric
Standard Model. Our results extend the previously calculated weak corrections
by including all one-loop corrections together with higher order QED
corrections. We present the details of the analytical calculation and discuss
the renormalization scheme. The numerical analysis shows the results for total
cross-sections, forward-backward and left-right asymmetries. It is based on the
SPS1a' point from the SPA project. The complete corrections are about 10% and
have to be taken into account in a high precision analysis.Comment: 32 pages, 24 figures, RevTeX
keV sterile neutrino dark matter in gauge extensions of the standard model
It is known that a keV scale sterile neutrino is a good warm dark matter
candidate. We study how this possibility could be realized in the context of
gauge extensions of the standard model. The na\"ive expectation leads to large
thermal overproduction of sterile neutrinos in this setup. However, we find
that it is possible to use out-of-equilibrium decay of the other right-handed
neutrinos of the model to dilute the present density of the keV sterile
neutrinos and achieve the observed dark matter density. We present the
universal requirements that should be satisfied by the gauge extensions of the
standard model, containing right-handed neutrinos, to be viable models of warm
dark matter, and provide a simple example in the context of the left-right
symmetric model.Comment: RevTex, 13 pages, 5 figures; journal version (corrected typos
Enhancement of W+/- H-/+ Production at Hadron Colliders in the Two Higgs Doublet Model
We discuss the associated W+/- H-/+ production at the CERN Large Hadron
Collider. The dependence of the hadronic cross section on the Higgs sector
parameters is investigated in detail in the framework of the general Two Higgs
Doublet Model (THDM). We study the possible enhancement of the THDM prediction
for the cross section compared to the prediction of the Minimal Supersymmetric
Standard Model (MSSM). We find regions in the THDM parameter space where the
THDM prediction can exceed the one of the MSSM by two orders of magnitude.
These regions of large cross section are in agreement with theoretical bounds
on the model, derived from the requirement of vacuum stability and perturbative
unitarity, and are not excluded by experimental constraints.Comment: 19 pages, 5 figure
Radiative Higgs Boson Decays H\to f\bar{f}\gamma Beyond the Standard Model
Neutral Higgs boson radiative decays of the form h_0, H, A \to
f\bar{f}\gamma, in the light fermion limit $m_f->0, are calculated in the two
Higgs doublet model at one-loop level. Comparisons with the calculation within
the standard model are given, which indicates that these two models are
distinguishable in the decay mode fermion-antifermion -photon. Our results show
that the concerned process may stand as an implement to identify the Higgs
belongings in case there is a intermediate mass Higgs detected.Comment: 13 pages in Revtex, version to appear in Phys. Rev.
QCD Correction to Neutralino Annihilation Process and Dark Matter Density in Supersymmetric Models
We calculate QCD correction to the neutralino annihilation cross section into
quark anti-quark final state and discuss its implications to the calculation of
neutralino relic density. We see that the QCD correction enhances the
pair-annihilation cross section by O(10 %) when final-state quarks are
non-relativistic. Consequently, when the lightest neutralinos dominantly
annihilate into a t\bar{t} pair, the relic density of the lightest neutralino
is significantly affected by the QCD correction, in particular when the
lightest-neutralino mass is close to the top-quark mass.Comment: 19 pages, 5 figure
Radion effects on the production of an intermediate-mass scalar and Z at LEP II
We have studied the process, where
is the Higgs and/or radion bosons. The implications of the radion effects on
the preliminary ALEPH data are also discussed. The case of the lighter radion
than Higgs boson is disfavored by the ALEPH analyses of the tagged four-jet
data, since the radion predominantly decays into two gluon jets due to the QCD
trace anomaly. If the radion is highly degenerate in mass with the Higgs, the
cross section can be increased more than at one sigma level, with natural scale
of the vacuum expectation value of the radion.Comment: 10 pages, 1 Postscript figure, final version to appear in PR
Split Two-Higgs-Doublet Model and Neutrino Condensation
We split the two-Higgs-doublet model by assuming very different vevs for the
two doublets: the vev is at weak scale (174 GeV) for the doublet \Phi_1 and at
neutrino-mass scale (10^{-2} \sim 10^{-3} eV) for the doublet \Phi_2. \Phi_1 is
responsible for giving masses to all fermions except neutrinos; while \Phi_2 is
responsible for giving neutrino masses through its tiny vev without introducing
see-saw mechanism. Among the predicted five physical scalars H, h, A^0 and
H^{\pm}, the CP-even scalar h is as light as 10^{-2} \sim 10^{-3}eV while
others are at weak scale. We identify h as the cosmic dark energy field and the
other CP-even scalar H as the Standard Model Higgs boson; while the CP-odd A^0
and the charged H^{\pm} are the exotic scalars to be discovered at future
colliders. Also we demonstrate a possible dynamical origin for the doublet
\Phi_2 from neutrino condensation caused by some unknown dynamics.Comment: version in Europhys. Lett. (discussions added
A Higgs Quadruplet for Type III Seesaw and Implications for and Conversion
In Type III seesaw model the heavy neutrinos are contained in leptonic
triplet representations. The Yukawa couplings of the triplet fermion and the
left-handed neutrinos with the doublet Higgs field produce the Dirac mass
terms. Together with the Majorana masses for the leptonic triplets, the light
neutrinos obtain non-zero seesaw masses. We point out that it is also possible
to have a quadruplet Higgs field to produce the Dirac mass terms to facilitate
the seesaw mechanism. The vacuum expectation value of the quadruplet Higgs is
constrained to be small by electroweak precision data. Therefore the Yukawa
couplings of a quadruplet can be much larger than those for a doublet. We also
find that unlike the usual Type III seesaw model where at least two copies of
leptonic triplets are needed, with both doublet and quadruplet Higgs
representations, just one leptonic triplet is possible to have a
phenomenologically acceptable model because light neutrino masses can receive
sizable contributions at both tree and one loop levels. Large Yukawa couplings
of the quadruplet can induce observable effects for lepton flavor violating
processes and conversion. Implications of the
recent limit from MEG and also limit on conversion
on Au are also given. Some interesting collider signatures for the doubly
charged Higgs boson in the quadruplet are discussed.Comment: Latex 11 pages, 1 figure. A few references adde
Trilinear Higgs couplings in the two Higgs doublet model with CP violation
We carry out a detailed analysis of the general two Higgs doublet model with
CP violation. We describe two different parametrizations of this model, and
then study the Higgs boson masses and the trilinear Higgs couplings for these
two parametrizations. Within a rather general model, we find that the trilinear
Higgs couplings have a significant dependence on the details of the model, even
when the lightest Higgs boson mass is taken to be a fixed parameter. We include
radiative corrections in the one-loop effective potential approximation in our
analysis of the Higgs boson masses and the Higgs trilinear couplings. The
one-loop corrections to the trilinear couplings of the two Higgs doublet model
also depend significantly on the details of the model, and can be rather large.
We study quantitatively the trilinear Higgs couplings, and show that these
couplings are typically several times larger than the corresponding Standard
Model trilinear Higgs coupling in some regions of the parameter space. We also
briefly discuss the decoupling limit of the two Higgs doublet model.Comment: 23 pages, 15 figures. v2: References added, version to appear in PR
Pair production of neutral Higgs bosons at the CERN Large Hadron Collider
We study the hadroproduction of two neutral Higgs bosons in the minimal
supersymmetric extension of the standard model, which provides a handle on the
trilinear Higgs couplings. We include the contributions from quark-antiquark
annihilation at the tree level and those from gluon-gluon fusion, which
proceeds via quark and squark loops. We list compact results for the tree-level
partonic cross sections and the squark loop amplitudes, and we confirm previous
results for the quark loop amplitudes. We quantitatively analyze the hadronic
cross sections at the CERN Large Hadron Collider assuming a favorable
supergravity-inspired scenario.Comment: 22 pages (Latex), 16 figures (Postscript). Discussion of theoretical
uncertainties and background processes added. Accepted for publication in
Phys. Rev.
- …