462 research outputs found
Top-Down Approach to Unified Supergravity Models
We introduce a new approach for studying unified supergravity models. In this
approach all the parameters of the grand unified theory (GUT) are fixed by
imposing the corresponding number of low energy observables. This determines
the remaining particle spectrum whose dependence on the low energy observables
can now be investigated. We also include some SUSY threshold corrections that
have previously been neglected. In particular the SUSY threshold corrections to
the fermion masses can have a significant impact on the Yukawa coupling
unification.Comment: 19 pages, uuencoded compressed ps file, DESY 94-057 (paper format
corrected
Electroweak Higgs as a pseudo-Goldstone boson of broken scale invariance
We point out that it is possible to associate the electroweak Higgs boson
with the pseudo-Goldstone boson of broken scale invariance, thus resolving the
hierarchy problem in a technically natural way. We illustrate this idea with
two specific gauge models. Besides being consistent with all currently
available experimental data, both models maintain the predictive power of the
standard model, since the first model has only one additional parameter beyond
the standard model, and the second has the same number of free parameters as
the standard model.Comment: 11 pages, discussion added, the version to appear in Phys. Lett.
Production of neutral MSSM Higgs bosons in collisions: a complete 1-loop calculation
We present the first complete 1-loop diagrammatic calculation of the cross
sections for the neutral Higgs production processes e^+e^-\ra Z^0h^0 and
e^+e^-\ra A^0h^0 in the minimal supersymmetric standard model. We compare the
results from the diagrammatic calculation with the corresponding ones of the
simpler and compact effective potential approximation and discuss the typical
size of the differences.Comment: LaTeX, 16 pages, 8 figures appended in a uuencoded file, complete
PostScript file available at
http://itpaxp1.physik.uni-karlsruhe.de/prep/KA-TP-16-1995/KA-TP-16-199
NonQCD contributions to heavy quark masses and sensitivity to Higgs mass
We find that if the Higgs mass is close to its present experimental lower
limit (100 GeV),Yukawa interactions in the quark-Higgs sector can make
substantial contributions to the heavy quark MS masses.Comment: 16 pages, 1 figure. Fixed a few typos (eqs (7),(34)
Remarks on the Upper Bounds on the Higgs Boson Mass from Triviality
We study the effects of the one-loop matching conditions on Higgs boson and
top quark masses on the triviality bounds on the Higgs boson mass using
with corrected two-loop coefficients. We obtain quite higher
results than previous ones and observe that the triviality bounds are not
nearly influenced by varying top quark mass over the range measured at CDF and
D0. The effects of typo errors in and the one-loop
matching condition on the top quark mass are negligible. We estimate the size
of effects on the triviality bounds from the one-loop matching condition on the
Higgs boson mass.Comment: 9 pages, tar'ed gzip'ed uuencoded files, LaTex, 5 PostScript figures.
To appear in Physical Review
MSSM Higgs Boson Phenomenology at the Tevatron Collider
The Higgs sector of the minimal supersymmetric standard model (MSSM) consists
of five physical Higgs bosons, which offer a variety of channels for their
experimental search. The present study aims to further our understanding of the
Tevatron reach for MSSM Higgs bosons, addressing relevant theoretical issues
related to the SUSY parameter space, with special emphasis on the radiative
corrections to the down--quark and lepton couplings to the Higgs bosons for
large . We performed a computation of the signal and backgrounds for
the production processes and at the upgraded Tevatron,
with being the neutral MSSM Higgs bosons. Detailed experimental
information and further higher order calculations are demanded to
confirm/refine these predictions.Comment: 47 pages, REVTex format, 15 figures; spacing changed to reduce
length, references added or moved within manuscript for clarity, some
rewording, labelling corrected on two figures, results unchange
Probing Minimal Supergravity at the CERN LHC for Large
For large values of the minimal supergravity model parameter , the
tau lepton and the bottom quark Yukawa couplings become large, leading to
reduced masses of -sleptons and -squarks relative to their first and
second generation counterparts, and to enhanced decays of charginos and
neutralinos to -leptons and -quarks. We evaluate the reach of the CERN
LHC collider for supersymmetry in the mSUGRA model parameter space. We
find that values of GeV can be probed with just 10
fb of integrated luminosity for values as high as 45, so
that mSUGRA cannot escape the scrutiny of LHC experiments by virtue of having a
large value of . We also perform a case study of an mSUGRA model at
where \tz_2\to \tau\ttau_1 and \tw_1\to \ttau_1\nu_\tau
with branching fraction. In this case, at least within our
simplistic study, we show that a di-tau mass edge, which determines the value
of m_{\tz_2}-m_{\tz_1}, can still be reconstructed. This information can be
used as a starting point for reconstructing SUSY cascade decays on an
event-by-event basis, and can provide a strong constraint in determining the
underlying model parameters. Finally, we show that for large there
can be an observable excess of leptons, and argue that signals
might serve to provide new information about the underlying model framework.Comment: 22 page REVTEX file including 8 figure
A No-Lose Theorem for Higgs Searches at a Future Linear Collider
Assuming perturbativity up to a high energy scale GeV, we
demonstrate that a future linear collider operating at
500 GeV with 500 fb per year (such as the recently
proposed TESLA facility) will detect a Higgs boson signal regardless of the
complexity of the Higgs sector and of how the Higgs bosons decay.Comment: 4 pages, LaTe
(B-L) Symmetry vs. Neutrino Seesaw
We compute the effective coupling of the Majoron to W bosons at \cO(\hbar)
by evaluating the matrix element of the (B-L) current between the vacuum and a
state. The (B-L) anomaly vanishes, but the amplitude does not vanish
as a result of a UV finite and non-local contribution which is entirely due to
the mixing between left-chiral and right-chiral neutrinos. The result shows how
anomaly-like couplings may arise in spite of the fact that the (B-L) current
remains exactly conserved to all orders in , lending additional support
to our previous proposal to identify the Majoron with the axion.Comment: 13 pages, 1 figure, with additional explanations and clarification
Grand Unification at Intermediate Mass Scales through Extra Dimensions
One of the drawbacks of conventional grand unification scenarios has been
that the unification scale is too high to permit direct exploration. In this
paper, we show that the unification scale can be significantly lowered (perhaps
even to the TeV scale) through the appearance of extra spacetime dimensions.
Such extra dimensions are a natural consequence of string theories with
large-radius compactifications. We show that extra spacetime dimensions
naturally lead to gauge coupling unification at intermediate mass scales, and
moreover may provide a natural mechanism for explaining the fermion mass
hierarchy by permitting the fermion masses to evolve with a power-law
dependence on the mass scale. We also show that proton-decay constraints may be
satisfied in our scenario due to the higher-dimensional cancellation of
proton-decay amplitudes to all orders in perturbation theory. Finally, we
extend these results by considering theories without supersymmetry;
experimental collider signatures; and embeddings into string theory. The latter
also enables us to develop several novel methods of explaining the fermion mass
hierarchy via -branes. Our results therefore suggest a new approach towards
understanding the physics of grand unification as well as the phenomenology of
large-radius string compactifications.Comment: 65 pages, LaTeX, 20 figure
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