138 research outputs found
Generalization of Einstein-Lovelock theory to higher order dilaton gravity
A higher order theory of dilaton gravity is constructed as a generalization
of the Einstein-Lovelock theory of pure gravity. Its Lagrangian contains terms
with higher powers of the Riemann tensor and of the first two derivatives of
the dilaton. Nevertheless, the resulting equations of motion are quasi-linear
in the second derivatives of the metric and of the dilaton. This property is
crucial for the existence of brane solutions in the thin wall limit. At each
order in derivatives the contribution to the Lagrangian is unique up to an
overall normalization. Relations between symmetries of this theory and the
O(d,d) symmetry of the string-inspired models are discussed.Comment: 18 pages, references added, version to be publishe
Particle Spectrum in the Non-Minimal Supersymmetric Standard Model with
We present a detailed discussion of the particle spectrum of the Non-Minimal
Supersymmetric Standard Model (NMSSM), containing two Higgs doublets and a
singlet, in the limit . This is compared with the
corresponding particle spectrum of the Minimal Supersymmetric Standard Model
(MSSM). In this limit the singlet vacuum expectation value is forced to be
large, of the order of TeV, and the singlet decouples from the lightest
scalar Higgs boson and the neutralinos. With the exception of the lightest
Higgs boson, the particle spectrum in the model turns out to be heavy. The
radiatively corrected lightest Higgs boson mass is in the neighbourhood of
GeV.Comment: 20 pages plain LaTeX and 3 figures supplied on request from
[email protected] or [email protected]
Can the SO(10) Model with Two Higgs Doublets Reproduce the Observed Fermion Masses?
It is usually considered that the SO(10) model with one 10 and one 126 Higgs
scalars cannot reproduce the observed quark and charged lepton masses. Against
this conventional conjecture, we find solutions of the parameters which can
give the observed fermion mass spectra. The SO(10) model with one 10 and one
120 Higgs scalars is also discussed.Comment: 7 pages, 1 figure, REVTe
Do electroweak precision data and Higgs-mass constraints rule out a scalar bottom quark with mass of O(5 GeV)?
We investigate the phenomenological implications of a light scalar bottom
quark, with a mass of about the bottom quark mass, within the minimal
supersymmetric standard model. The study of such a scenario is of theoretical
interest, since, depending on their production and decay modes, light sbottoms
may have escaped experimental detection up to now and, in addition, may
naturally appear for large values of \tan\beta. In this article we show that
such a light sbottom cannot be ruled out by the constraints from the
electroweak precision data and the present bound on the lightest CP-even Higgs
boson mass at LEP. It is inferred that a light sbottom scenario requires in
general a relatively light scalar top quark whose mass is typically about the
top-quark mass. It is also shown that under these conditions the lightest
CP-even Higgs boson decays predominantly into scalar bottom quarks in most of
the parameter space and that its mass is restricted to m_h ~< 123 GeV.Comment: 7 pages, 2 figures, LateX. Discussion about fine tuning and
low-energy experiments enlarged. Version to appear in Phys. Rev. Let
Heavy top quark from Fritzsch mass matrices
It is shown, contrary to common belief, that the Fritzsch ansatz for the
quark mass matrices admits a heavy top quark. With the ansatz prescribed at the
supersymmetric grand unified (GUT) scale, one finds that the top quark may be
as heavy as 145 GeV, provided that tan (the ratio of the vacuum
expectation values of the two higgs doublets) . Within a
non-supersymmetric GUT framework with two (one) light higgs doublets, the
corresponding approximate upper bound on the top mass is GeV. Our
results are based on a general one--loop renormalization group analysis of the
quark masses and mixing angles and are readily applied to alternative mass
matrix ans\"{a}tze.Comment: LaTeX, 14 figures (not included, available on request
Predictions for Higgs and SUSY spectra from SO(10) Yukawa Unification with mu > 0
We use Yukawa unification to constrain SUSY parameter space. We
find a narrow region survives for (suggested by \bsgam and the
anomalous magnetic moment of the muon) with , , \gev and \gev. Demanding Yukawa unification thus makes definite predictions for
Higgs and sparticle masses.Comment: 10 pages, 3 figures, revised version to be published in PR
Light Higgsino Detection at LEP1.5
Within the minimal supersymmetric extension of the Standard Model, the best
fit to the most recent precision-measurement data requires charginos and
neutralinos, with dominant Higgsino components and with masses within the reach
of LEP1.5 ( GeV). In this work, we present a detailed analysis of
the neutralino and chargino production processes for the favoured region of
parameter space, that is low values of and either low or large values
of . We find that chargino and neutralino searches can cover the
Higgsino region in the () plane for values of M_2 \simlt 1 TeV, at
the next phases of the LEP collider. We also show that, due mainly to
phase-space constraints, the lightest neutralinos should be more easily
detectable than charginos in most of the parameter space preferred by
precision-measurement data.Comment: 16 pages, 8 Figures, LateX. Figures now include initial state
radiation effects on the cross sections
Supersymmetric Models With Tan(beta) Close to Unity
Within the framework of supersymmetric grand unification, estimates of the
quark mass based on the asymptotic relation single out
the region with close to unity, particularly if . We explore the radiative breaking of the
electroweak symmetry and the associated sparticle and higgs spectroscopy in
models with . The lightest scalar higgs
is expected to have a mass below , while the remaining four higgs
masses exceed . The lower bounds on some of the sparticle masses are
within the range of LEP 200.Comment: 13 pages in plain LaTeX, BA-94-02, 15 figures (available on request
Sparticle Mass Spectra from SO(10) Grand Unified Models with Yukawa Coupling Unification
We examine the spectrum of superparticles obtained from the minimal SO(10)
grand unified model, where it is assumed the gauge symmetry breaking yields the
Minimal Supersymmetric Standard Model (MSSM) as the effective theory at
GeV. In this model, unification of Yukawa
couplings implies a value of . At such high values of
, assuming universality of scalar masses, the usual mechanism of
radiative electroweak symmetry breaking breaks down. We show that a set of weak
scale sparticle masses consistent with radiative electroweak symmetry breaking
can be generated by imposing non-universal GUT scale scalar masses consistent
with universality within SO(10) plus extra -term contributions associated
with the reduction in rank of the gauge symmetry group when SO(10)
spontaneously breaks to . We comment upon the
consequences of the sparticle mass spectrum for collider searches for
supersymmetry. One implication of SO(10) unification is that the light bottom
squark can be by far the lightest of the squarks. This motivates a dedicated
search for bottom squark pair production at and colliders.Comment: 12 page REVTEX file including 3 PS figures; revised manuscript
includes minor changes to coincide with published versio
- …