29 research outputs found
What is the upper limit on the lightest supersymmetric Higgs mass?
In this talk the question of what is the upper bound on the lightest
supersymmetric Higgs mass, m_h is addressed. This question is relevant since
experimental lower bounds on m_h might implement, in the near future, exclusion
of supersymmetry. By imposing (perturbative) unification of the gauge couplings
at some high scale \simgt 10^{17} GeV, we have found that for a top-quark mass
M_t=175 GeV, and depending on the supersymmetric parameters, this bound can be
as high as 205 GeV.Comment: 7 pages, 4 figures, Work presented at PASCOS-98, March 22-29 199
Phantom Higgs from Unparticles
A renormalizable coupling between the Higgs and a scalar unparticle operator
O_U of non-integer dimension d_U < 2 gives rise, after electroweak symmetry
breaking, to a mass gap in the unparticle continuum and a shift in the original
Higgs mass, which can end up above or below the mass gap. We show that, besides
the displaced Higgs state, a new isolated state can generically appear in the
spectrum near or below the mass gap. Such state (which we call phantom Higgs)
is a mixture of Higgs and unparticles and therefore has universally reduced
couplings to fermions and gauge bosons. This phenomenon could cause the mass of
the lightest Higgs state accessible to colliders to be much smaller than the
mass expected from the SM Lagrangian.Comment: 14 LaTeX pages, 6 figure
Phase structure and phase transitions of the SU(2) x O(N) symmetric scalar field theory
Radiatively induced SU(2) symmetry breaking is shown to be a genuine feature
of SU(2) x O(N) globally symmetric renormalisable field theories in the large N
limit, describing interaction of a complex SU(2) doublet, O(N)-singlet field
with an SU(2) singlet, O(N) vector. Symmetry breaking solutions are found even
when all fields have positive renormalised squared mass. The emerging novel
mechanism of symmetry breaking can reproduce with a choice of N~300 the
standard range of the electroweak condensate and the Higgs mass occurring in
the extended Higgs dynamics of an SU(2) symmetric Gauge+Higgs model.Comment: 6 pages, 3 figures; the role of the cut-off in the effective theory
is discussed, references added; to appear in Europhys. Let
Signatures of Baryogenesis in the MSSM
We revisit the electroweak baryogenesis within the context of the minimal
supersymmetric standard model (MSSM), studying its potential collider
signatures. We find that this mechanism of baryogenesis does not give a new CP
violating signal at the -factories. The first circumstantial evidence may
come from enhanced or mixing. If a light right-handed scalar top
and Higgs are found as required, a linear collider represents the best
possibility for confirming the scenario.Comment: 5 pages, 2 figures. Minor typos fixed. Reference Adde
Electroweak baryogenesis
Electroweak baryogenesis (EWBG) remains a theoretically attractive and
experimentally testable scenario for explaining the cosmic baryon asymmetry. We
review recent progress in computations of the baryon asymmetry within this
framework and discuss their phenomenological consequences. We pay particular
attention to methods for analyzing the electroweak phase transition and
calculating CP-violating asymmetries, the development of Standard Model
extensions that may provide the necessary ingredients for EWBG, and searches
for corresponding signatures at the high energy, intensity, and cosmological
frontiers.Comment: 42 pages, 13 figures, invited review for the New Journal of Physics
focus issue on 'Origin of Matter
High Temperature Phase Transition in Two-Scalar Theories
Two-scalar theories at high temperature exhibit a rich spectrum of possible
critical behaviour, with a second or first order phase transition. In the
vicinity of the critical temperature one can observe critical exponents,
tricritical points and crossover behaviour. None of these phenomena are visible
to high temperature perturbation theory.Comment: 39 pages, macro equation.sty included, 11 uuencoded figures
Top-squark searches at the Tevatron in models of low-energy supersymmetry breaking
We study the production and decays of top squarks (stops) at the Tevatron
collider in models of low-energy supersymmetry breaking. We consider the case
where the lightest Standard Model (SM) superpartner is a light neutralino that
predominantly decays into a photon and a light gravitino. Considering the
lighter stop to be the next-to-lightest Standard Model superpartner, we analyze
stop signatures associated with jets, photons and missing energy, which lead to
signals naturally larger than the associated SM backgrounds. We consider both
2-body and 3-body decays of the top squarks and show that the reach of the
Tevatron can be significantly larger than that expected within either the
standard supergravity models or models of low-energy supersymmetry breaking in
which the stop is the lightest SM superpartner. For a modest projection of the
final Tevatron luminosity, L = 4 fb-1, stop masses of order 300 GeV are
accessible at the Tevatron collider in both 2-body and 3-body decay modes. We
also consider the production and decay of ten degenerate squarks that are the
supersymmetric partners of the five light quarks. In this case we find that
common squark masses up to 360 GeV are easily accessible at the Tevatron
collider, and that the reach increases further if the gluino is light.Comment: 32 pages, 9 figures; references adde
Constraints on Astro-unparticle Physics from SN 1987A
SN 1987A observations have been used to place constraints on the interactions
between standard model particles and unparticles. In this study we calculate
the energy loss from the supernovae core through scalar, pseudo scalar, vector,
pseudo vector unparticle emission from nuclear bremsstrahlung for degenerate
nuclear matter interacting through one pion exchange. In order to examine the
constraints on we considered the emission of scalar, pseudo
scalar, vector, pseudo vector and tensor through the pair annihilation process
. In addition we have re-examined other pair
annihilation processes. The most stringent bounds on the dimensionless coupling
constants for and are obtained from
nuclear bremsstrahlung process for the pseudo scalar and pseudo-vector
couplings and for
tensor interaction, the best limit on dimensionless coupling is obtained from
and we get .Comment: 12 pages, 2 postscript figure
Constraints from Solar and Reactor Neutrinos on Unparticle Long-Range Forces
We have investigated the impact of long-range forces induced by unparticle
operators of scalar, vector and tensor nature coupled to fermions in the
interpretation of solar neutrinos and KamLAND data. If the unparticle couplings
to the neutrinos are mildly non-universal, such long-range forces will not
factorize out in the neutrino flavour evolution. As a consequence large
deviations from the observed standard matter-induced oscillation pattern for
solar neutrinos would be generated. In this case, severe limits can be set on
the infrared fix point scale, Lambda_u, and the new physics scale, M, as a
function of the ultraviolet (d_UV) and anomalous (d) dimension of the
unparticle operator. For a scalar unparticle, for instance, assuming the
non-universality of the lepton couplings to unparticles to be of the order of a
few per mil we find that, for d_UV=3 and d=1.1, M is constrained to be M >
O(10^9) TeV (M > O(10^10) TeV) if Lambda_u= 1 TeV (10 TeV). For given values of
Lambda_u and d, the corresponding bounds on M for vector [tensor] unparticles
are approximately 100 [3/Sqrt(Lambda_u/TeV)] times those for the scalar case.
Conversely, these results can be translated into severe constraints on
universality violation of the fermion couplings to unparticle operators with
scales which can be accessible at future colliders.Comment: 13 pages, 3 figures. Minor changes due to precision in numerical
factors and correction in figure labels. References added. Conclusions remain
unchange
Higgs Physics at LEP2
In this report we review the prospects for Higgs physics at LEP2. The
theoretical aspects and the phenomenology of Higgs particles are discussed
within the Standard Model (SM) and the Minimal Supersymmetric Standard Model
(MSSM). The experimental search techniques are described and the discovery
limits for Higgs bosons in the LEP2 energy range are summarized. In addition,
opportunities of detecting Higgs particles in non-minimal extensions of the SM
and the MSSM are investigated.Comment: 112 pages, latex file + figures (some bitmapped), to appear in Vol.
1, Report of the Workshop on Physics at LEP2, G. Altarelli, T. Sjostrand and
F.Zwirner (eds), CERN 96-01. (Full postscript and uuencoded files, including
full resolution figures are available at the www address
http://surya11.cern.ch/surya_info/users/mcarena in finrep.ps, finrep.uu