760 research outputs found
Upper limit on mh in the MSSM and M-SUGRA vs. prospective reach of LEP
The upper limit on the lightest CP-even Higgs boson mass, mh, is analyzed
within the MSSM as a function of tan(beta) for fixed mtop and Msusy. The impact
of recent diagrammatic two-loop results on this limit is investigated. We
compare the MSSM theoretical upper bound on mh with the lower bound obtained
from experimental searches at LEP. We estimate that with the LEP data taken
until the end of 1999, the region mh < 108.2 GeV can be excluded at the 95%
confidence level. This corresponds to an excluded region 0.6 <= tan(beta) <=
1.9 within the MSSM for mtop = 174.3 GeV and Msusy <= 1 TeV. The final
exclusion sensitivity after the end of LEP, in the year 2000, is also briefly
discussed. Finally, we determine the upper limit on mh within the Minimal
Supergravity (M-SUGRA) scenario up to the two-loop level, consistent with
radiative electroweak symmetry breaking. We find an upper bound of mh \approx
127 GeV for mtop = 174.3 GeV in this scenario, which is slightly below the
bound in the unconstrained MSSM.Comment: 10 pages, 3 figure
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
LHC phenomenology of supersymmetric models beyond the MSSM
We discuss various phenomenological aspects of supersymmetric models beyond
the MSSM. A particular focus is on models which can correctly explain neutrino
data and the possiblities of LHC to identify the underlying scenario.Comment: Contribution to the 16th International Symposium on Particles,
Strings and Cosmology (PASCOS 2010), Valencia (Spain), July 19-23, 201
B_{s,d} -> l^+ l^- and K_L -> l^+ l^- in SUSY models with non-minimal sources of flavour mixing
We present a general analysis of B_{s,d}-> l^+ l^- and K_L -> l^+ l^- decays
in supersymmetric models with non-minimal sources of flavour mixing. In spite
of the existing constraints on off-diagonal squark mass terms, these modes
could still receive sizeable corrections, mainly because of Higgs-mediated
FCNCs arising at large tan(beta). The severe limits on scenarios with large
tan(beta) and non-negligible {tilde d}^i_{R(L)}-{d-tilde}^j_{R(L)} mixing
imposed by the present experimental bounds on these modes and Delta B=2
observables are discussed in detail. In particular, we show that scalar-current
contributions to K_L -> l^+ l^- and B-{bar B} mixing set non-trivial
constraints on the possibility that B_s -> l^+ l^- and B_d -> l^+ l^- receive
large corrections.Comment: 18 pages, 4 figures (v2: minor changes, published version
SUSY Parameter Analysis at TeV and Planck Scales
Coherent analyses at future LHC and LC experiments can be used to explore the
breaking mechanism of supersymmetry and to reconstruct the fundamental theory
at high energies, in particular at the grand unification scale. This will be
exemplified for minimal supergravity.Comment: 7 pages, 3 figures, uses espcrc2.sty (included), Proceedings, Loops
and Legs 2004, Zinnowitz on Usedo
b-tau Unification and neutrino masses in SU(5) extensions of the MSSM with radiative electroweak symmetry breaking
We make a complete analysis of the Yukawa coupling unification in SU(5)
extensions of the MSSM in the framework of the radiative symmetry breaking
scenario. Both logarithmic and finite threshold corrections of sparticles have
been included in the determination of the gauge and Yukawa couplings at M_Z.
The effect of the heavy masses of each model in the renormalization group
equations is also included. We find that in the minimal SU(5) model b-tau
Yukawa unification can be achieved for too large a value of alpha_s. On the
other hand the Peccei-Quinn version of the Missing Doublet model, with the
effect of the right handed neutrino also included, exhibits b-tau unification
in excellent agreement with all low energy experimental data. Unification of
all Yukawa couplings is also discussed.Comment: 20 pages, LaTeX2e,uses psfig,5 figures,full postscript file available
at http://artemis.cc.uoi.gr/~adedes/new97.ps.g
Hunting a light CP-violating Higgs via diffraction at the LHC
We study the central diffractive production of the (three neutral) Higgs
bosons, with a rapidity gap on either side, in an MSSM scenario with
CP-violation. We consider the bb-bar and tautau-bar decay for the light H_1
boson and the four b-jet final state for the heavy H_2 and H_3 bosons, and
discuss the corresponding backgrounds. A direct indication of the existence of
CP-violation can come from the observation of either an azimuthal asymmetry in
the angular distribution of the tagged forward protons (for the exclusive pp ->
p+H+p process) or of a sin(2phi) contribution in the azimuthal correlation
between the transverse energy flows in the proton fragmentation regions for the
process with the diffractive dissociation of both incoming protons (pp ->
X+H+Y). We emphasise the advantage of reactions with the rapidity gaps (that is
production by the pomeron-pomeron fusion) to probe CP parity and to determine
the quantum numbers of the produced central object.Comment: 11 pages, 3 figure
Self-duality and vacuum selection
I propose that self-duality in quantum phase-space provides the criteria for
the selection of the quantum gravity vacuum. The evidence for this assertion
arises from two independent considerations. The first is the phenomenological
success of the free fermionic heterotic-string models, which are constructed in
the vicinity of the self-dual point under T-duality. The relation between the
free fermionic models and the underlying Z2 X Z2 toroidal orbifolds is
discussed. Recent analysis revealed that the Z2 X Z2 free fermionic orbifolds
utilize an asymmetric shift in the reduction to three generations, which
indicates that the untwisted geometrical moduli are fixed near the self-dual
point. The second consideration arises from the recent formulation of quantum
mechanics from an equivalence postulate and its relation to phase-space
duality. In this context it is demonstrated that the trivial state, with
V(q)=E=0, is identified with the self-dual state under phase-space duality.
These observations suggest a more general mathematical principle in operation.
In physical systems that exhibit a duality structure, the self-dual states
under the given duality transformations correspond to critical points.Comment: 40 pages. Standard Latex. 1 figur
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