124 research outputs found
Infrared quasi-fixed solutions in the NMSSM
The considerable part of the parameter space in the MSSM corresponding to the
infrared quasi fixed point scenario is almost excluded by LEP II bounds on the
lightest Higgs boson mass. In the NMSSM the mass of the lightest Higgs boson
reaches its maximum value in the strong Yukawa coupling limit when Yukawa
couplings are essentially larger than gauge ones at the Grand Unification
scale. In this limit the solutions of the renormalisation group equations are
attracted to the infrared and Hill type effective fixed lines or surfaces in
the Yukawa coupling parameter space. They are concentrated in the vicinity of
quasi fixed points for . However the solutions are attracted
to such points rather weakly. For this reason when all the
solutions of the renormalisation group equations are gathered near a line in
the Hill type effective surface. In the paper the approximate solutions for the
NMSSM Yukawa couplings are given. The possibility of --quark and
--lepton Yukawa coupling unification at the scale is also
discussed.Comment: 32 pages, 8 figures included, LaTeX 2
Survival probability for exclusive central diffractive production of colorless states at the LHC
In this paper we discuss the survival probability for exclusive central
diffractive production of a colorless small size system at the LHC. This
process has a clear signature of two large rapidity gaps. Using the eikonal
approach for the description of soft interactions, we predict the value of the
survival probability to be about 5~6% for single channel models, while for a
two channel model the survival probability is about 3%. The dependence of the
survival probability factor (damping factor) on the transverse momenta of the
recoiled protons is discussed, and we suggest it be measured at the Tevatron so
as to minimize the possible ambiguity in the calculation of survival
probability at the LHC.Comment: 33 pages, 26 figure
Higgs bosons in the simplest SUSY models
Nowadays in the MSSM the moderate values of are almost excluded
by LEP II lower bound on the lightest Higgs boson mass. In the Next-to-Minimal
Supersymmetric Standard Model the theoretical upper bound on it increases and
reaches maximal value in the strong Yukawa coupling limit when all solutions of
renormalization group equations are concentrated near the quasi-fixed point.
For calculation of Higgs boson spectrum the perturbation theory method can be
applied. We investigate the particle spectrum in the framework of the modified
NMSSM which leads to the self-consistent solution in the strong Yukawa coupling
limit. This model allows one to get GeV at values of
. In the investigated model the lightest Higgs boson mass
does not exceed GeV. The upper bound on the lightest CP-even
Higgs boson mass in more complicated supersymmetric models is also discussed.Comment: 27 pages, 5 figures included, LaTeX 2e. Plenary talk at the
Conference of RAS Nuclear Physics Department 2000 in ITEP, Moscow, Russia; to
appear in Phys. Atom. Nuc
HERA Physics Beyond the Standard Model
The prospects of physics beyond the standard model in deep inelastic
scattering are reviewed, emphasizing some scenarios which attained attention
after the observation of an excess of events with large momentum transfer at
HERA.Comment: 8 pages, LaTeX, uses iop style files and axodraw.sty, Talk presented
at the 3rd UK Phenomenology Workshop on HERA Physics, September 1998, Durha
Determining neutrino absorption spectra at Ultra-High Energies
A very efficient method to measure the flux of Ultra-high energy (UHE)
neutrinos is through the detection of radio waves which are emitted by the
particle shower in the lunar regolith. The highest acceptance is reached for
radio waves in the frequency band of 100-200 MHz which can be measured with
modern radio telescopes. In this work we investigate the sensitivity of this
detection method to structures in the UHE neutrino spectrum caused by their
absorption on the low-energy relic anti-neutrino background through the Z-boson
resonance. The position of the absorption peak is sensitive to the neutrino
mass and the redshift of the source. A new generation of low-frequency digital
radio telescopes will provide excellent detection capabilities for measuring
these radio pulses, thus making our consideration here very timely.Comment: 7 figures, submitted to JCAP revision: References updated and minor
changes in tex
Discriminating graviton exchange effects from other new physics scenarios in e^+e^- collisions
We study the possibility of uniquely identifying the effects of graviton
exchange from other new physics in high energy e^+e^- annihilation into
fermion-pairs. For this purpose, we use as basic observable a specific
asymmetry among integrated differential distributions, that seems particularly
suitable to directly test for such gravitational effects in the data analysis.Comment: 18 pages, including figures; v2: additional references and
acknowledgements. To appear in PR
Production of Two Non-Conjugate Leptoquarks in Collisions
We study the production of scalar and vector leptoquarks in
scattering. We use the most general couplings to the known fermions which are
dimensionless, baryon and lepton number conserving, and invariant. Expressions are presented for production
cross sections and predictions are given for future linear colliders.Comment: 14 page
External Fields as a Probe for Fundamental Physics
Quantum vacuum experiments are becoming a flexible tool for investigating
fundamental physics. They are particularly powerful for searching for new light
but weakly interacting degrees of freedom and are thus complementary to
accelerator-driven experiments. I review recent developments in this field,
focusing on optical experiments in strong electromagnetic fields. In order to
characterize potential optical signatures, I discuss various low-energy
effective actions which parameterize the interaction of particle-physics
candidates with optical photons and external electromagnetic fields.
Experiments with an electromagnetized quantum vacuum and optical probes do not
only have the potential to collect evidence for new physics, but
special-purpose setups can also distinguish between different particle-physics
scenarios and extract information about underlying microscopic properties.Comment: 12 pages, plenary talk at QFEXT07, Leipzig, September 200
Identification of extra neutral gauge bosons at the International Linear Collider
Heavy neutral gauge bosons, Z's, are predicted by many theoretical schemes of
physics beyond the Standard Model, and intensive searches for their signatures
will be performed at present and future high energy colliders. It is quite
possible that Z's are heavy enough to lie beyond the discovery reach expected
at the CERN Large Hadron Collider LHC, in which case only indirect signatures
of Z' exchanges may occur at future colliders, through deviations of the
measured cross sections from the Standard Model predictions. We here discuss in
this context the foreseeable sensitivity to Z's of fermion-pair production
cross sections at an e^+e^- linear collider, especially as regards the
potential of distinguishing different Z' models once such deviations are
observed. Specifically, we assess the discovery and identification reaches on
Z' gauge bosons pertinent to the E_6, LR, ALR and SSM classes of models, that
should be attained at the planned International Linear Collider (ILC). With the
high experimental accuracies expected at the ILC, the discovery and the
identification reaches on the Z' models under consideration could be increased
substantially. In particular, the identification among the different models
could be achieved for values of Z' masses in the discovery (but beyond the
identification) reach of the LHC. An important role in enhancing such reaches
is played by the electron (and possibly the positron) longitudinally polarized
beams. Also, although the purely leptonic processes are experimentally cleaner,
the measurements of c- and b-quark pair production cross sections are found to
carry important, and complementary, information on these searches.Comment: 21 page
Infrared Quasi Fixed Point Structure in Extended Yukawa Sectors and Application to R-parity Violation
We investigate one-loop renormalization group evolutions of extended sectors
of Yukawa type couplings. It is shown that Landau Poles which usually provide
necessary low energy upper bounds that saturate quickly with increasing initial
value conditions, lead in some cases to the opposite behaviour: some of the low
energy couplings decrease and become vanishingly small for increasingly large
initial conditions. We write down the general criteria for this to happen in
typical situations, highlighting a concept of {\sl repulsive} quasi-fixed
points, and illustrate the case both within a two-Yukawa toy model as well as
in the minimal supersymmetric standard model with R-parity violation. In the
latter case we consider the theoretical upper bounds on the various couplings,
identifying regimes where are
dynamically suppressed due to the Landau Pole. We stress the importance of
considering a large number of couplings simultaneously. This leads altogether
to a phenomenologically interesting seesaw effect in the magnitudes of the
various R-parity violating couplings, complementing and in some cases improving
the existing limits.Comment: Latex, 33 pages, 6 figure
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