2,223 research outputs found
Status of effective potential calculations
We review various effective potential methods which have been useful to
compute the Higgs mass spectrum and couplings of the minimal supersymmetric
standard model. We compare results where all-loop next-to-leading-log
corrections are resummed by the renormalization group, with those where just
the leading-log corrections are kept. Pole masses are obtained from running
masses by addition of convenient self-energy diagrams. Approximate analytical
expressions are worked out, providing an excellent approximation to the
numerical results which include all next-to-leading-log terms. An appropriate
treatment of squark decoupling allows to consider large values of the stop
and/or sbottom mixing parameters and thus fix a reliable upper bound on the
mass of the lightest CP-even Higgs boson mass.Comment: 10 pages, latex + psfig.sty, 6 figures uuencoded. Based on talk given
at the SUSY-95 International Workshop on Supersymmetry and Unification of
Fundamental Interactions, 15-19 May 199
Split extended supersymmetry from intersecting branes
We study string realizations of split extended supersymmetry, recently
proposed in hep-ph/0507192. Supersymmetry is broken by small ()
deformations of intersection angles of -branes giving tree-level masses of
order , where is the string scale, to localized
scalars. We show through an explicit one-loop string amplitude computation that
gauginos acquire hierarchically smaller Dirac masses . We also evaluate the one-loop Higgsino mass, , and show that,
in the absence of tree-level contributions, it behaves as . Finally we discuss an alternative suppression of scales using
large extra dimensions. The latter is illustrated, for the case where the gauge
bosons appear in N=4 representations, by an explicit string model with Standard
Model gauge group, three generations of quarks and leptons and gauge coupling
unification.Comment: 32 pages, 3 figure
Bounds on the Higgs mass in the Standard Model and the Minimal Supersymmetric Standard Model
Depending on the Higgs-boson and top-quark masses, and , the
effective potential of the {\bf Standard Model} can develop a non-standard
minimum for values of the field much larger than the weak scale. In those cases
the standard minimum becomes metastable and the possibility of decay to the
non-standard one arises. Comparison of the decay rate to the non-standard
minimum at finite (and zero) temperature with the corresponding expansion rate
of the Universe allows to identify the region, in the (, ) plane,
where the Higgs field is sitting at the standard electroweak minimum. In the
{\bf Minimal Supersymmetric Standard Model}, approximate analytical expressions
for the Higgs mass spectrum and couplings are worked out, providing an
excellent approximation to the numerical results which include all
next-to-leading-log corrections. An appropriate treatment of squark decoupling
allows to consider large values of the stop and/or sbottom mixing parameters
and thus fix a reliable upper bound on the mass of the lightest CP-even Higgs
boson mass. The discovery of the Higgs boson at LEP~2 might put an upper bound
(below the Planck scale) on the scale of new physics and eventually
disentangle between the Standard Model and the Minimal Supersymmetric Standard
Model.Comment: 13 pages, latex + sprocl + psfig.sty, 6 uuencoded figures. Based on
talk given at the International Workshop on Elementary Particle Physics:
Present and Future, Valencia, June 5 to 9, 199
The Lightest Higgs Boson Mass in the Minimal Supersymmetric Standard Model
We compute the upper bound on the mass of the lightest Higgs boson in the
Minimal Supersymmetric Standard Model in a model-independent way, including
leading (one-loop) and next-to-leading order (two-loop) radiative corrections.
We find that (contrary to some recent claims) the two-loop corrections are
negative with respect to the one-loop result and relatively small (\simlt
3\%). After defining physical (pole) top quark mass , by including QCD
self-energies, and physical Higgs mass , by including the electroweak
self-energies , we obtain the upper limit on
as a function of supersymmetric parameters. We include as supersymmetric
parameters the scale of supersymmetry breaking , the value of
and the mixing between stops (which is responsible
for the threshold correction on the Higgs quartic coupling). Our results do not
depend on further details of the supersymmetric model. In particular, for
TeV, maximal threshold effect and any value of
, we find GeV for GeV. In the particular
scenario where the top is in its infrared fixed point we find GeV
for GeV.Comment: 24 pages + 15 figures in one compressed uuencoded tarred postscript
file (The figures can be obtained by e-mail from [email protected]; also,
the whole postscript file of the text including the figures can be obtained
by ANONYMOUS FTP from ROCA.CSIC.ES (161.111.20.20) at the directory HEP the
file being HIGGS.PS: just type GET HEP/HIGGS.PS), Latex, CERN-TH.7334/9
Some Cosmological Implications of Hidden Sectors
We discuss some cosmological implications of extensions of the Standard Model
with hidden sector scalars coupled to the Higgs boson. We put special emphasis
on the conformal case, in which the electroweak symmetry is broken radiatively
with a Higgs mass above the experimental limit. Our refined analysis of the
electroweak phase transition in this kind of models strengthens the prediction
of a strongly first-order phase transition as required by electroweak
baryogenesis. We further study gravitational wave production and the
possibility of low-scale inflation as well as a viable dark matter candidate.Comment: 23 pages, 8 figures; some comments added, published versio
The Higgs as a Portal to Plasmon-like Unparticle Excitations
A renormalizable coupling between the Higgs and a scalar unparticle operator
O_U of non-integer dimension d_U<2 triggers, after electroweak symmetry
breaking, an infrared divergent vacuum expectation value for O_U. Such IR
divergence should be tamed before any phenomenological implications of the
Higgs-unparticle interplay can be drawn. In this paper we present a novel
mechanism to cure that IR divergence through (scale-invariant) unparticle
self-interactions, which has properties qualitatively different from the
mechanism considered previously. Besides finding a mass gap in the unparticle
continuum we also find an unparticle pole reminiscent of a plasmon resonance.
Such unparticle features could be explored experimentally through their mixing
with the Higgs boson.Comment: 12 LaTeX pages, 2 figure
The lightest Higgs mass in supersymmetric models with extra dimensions
In the four-dimensional supersymmetric standard model extended with gauge
singlets the lightest Higgs boson mass, , has an important contribution
proportional to the squared of the superpotential coupling of
singlets to Higgs fields, . The requirement of
perturbativity up to the unification scale yields an upper bound on GeV. In extensions to theories with (longitudinal) extra dimensions at the
TeV where such coupling exists and massive Kaluza-Klein states fall into N=2
representations, if either of the Higgs or singlet fields live in the bulk of
the extra dimensions, the -function of is suppressed due to
the absence of anomalous dimension of hypermultiplets to leading order. This
implies a slower running of and an enhancement of its low energy
value. The upper bound increases to values GeV.Comment: Latex2e, 11 pages, 1 figur
Refining the predictions of supersymmetric CP-violating models: A top-down approach
We explore in detail the consequences of the CP-violating phases residing in
the supersymmetric and soft SUSY breaking parameters in the approximation that
family flavour mixings are ignored. We allow for non-universal boundary
conditions and in such a consideration the model is described by twelve
independent CP-violating phases and one angle which misaligns the vacuum
expectation values (VEVs) of the Higgs scalars. We run two-loop renormalization
group equations (RGEs), for all parameters involved, including phases, and we
properly treat the minimization conditions using the one-loop effective
potential with CP-violating phases included. We show that the two-loop running
of phases may induce sizable effects for the electric dipole moments (EDMs)
that are absent in the one-loop RGE analysis. Also important corrections to the
EDMs are induced by the Higgs VEVs misalignment angle which are sizable in the
large tanb region. Scanning the available parameter space we seek regions
compatible with accelerator and cosmological data with emphasis on rapid
neutralino annihilations through a Higgs resonance. It is shown that large
CP-violating phases, as required in Baryogenesis scenarios, can be tuned to
obtain agreement with WMAP3 cold dark matter constraints, EDMs and all
available accelerator data, in extended regions of the parameter space which
may be accessible to LHC.Comment: 41 pages, 22 eps figures. A reference added and a typo corrected;
version to appear in JHE
- …