740 research outputs found
Resonant single chargino and neutralino versus fermion-antifermion production at the Linear Collider
We study single superparticle productions at the linear collider, putting
particular emphasis on resonant processes. We find that there exists a wide
region of model parameters where single chargino and neutralino productions
dominate over R-violating fermion-antifermion final states. For certain values
of mu and M_2 it is possible to produce even the heavier charginos and
neutralinos at significant rates, amplifying the total cross section and
obtaining interesting chains of cascade decays. Effects from initial-state
radiation are also included.Comment: 7 pages, 3 figures. Presented at the 2nd ECFA/DESY study on Linear
Colliders, Frascati, November 1998 (alternative theories working group).
Typos correcte
Inflation from superstrings
We investigate the possibility of obtaining inflationary solutions of the
slow roll type from a low energy Lagrangian coming from superstrings. The
advantage of such an approach is that in these theories the scalar potential
has only one free parameter (the Planck scale) and therefore no unnatural fine
tuning may be accommodated. We find that in any viable scheme the dilaton and
the moduli fields have to be stabilized and that before this happens, no other
field may be used as the inflaton. Then inflation may occur due to chiral
matter fields. Demanding that the potential terms associated with the chiral
fields do not spoil the dilaton and moduli minimization leads to severe
constraints on the magnitude of the density fluctuations.Comment: 22 pages, no figures, latex file We have corrected the magnitude of
the density fluctuations, which become smaller than the COBE ones. Some
references have also been added, and a few misprints correcte
Investigating the Supersymmetric Explanation of Anomalous CDF lepton(s) photon(s) Missing-E_T Events
The recent excess over the Standard Model prediction in the \mu \gamma
missing-E_T channel reported by CDF can be well-explained by resonant smuon
production with a single dominant R-parity violating coupling \lambda'_{211},
in the context of models where the gravitino is the lightest supersymmetric
particle. The slepton decays to the lightest neutralino and a muon followed by
neutralino decaying to a gravitino and photon. The kinematical distributions
are fitted well by our hypothesis and we use them to constrain the available
parameter space. The model also provides an explanation for the ee\gamma\gamma
missing-E_T event observed in Run I of the Tevatron by the CDF experiment. Our
model predicts an excess of between 5 and 35 events in a \gamma missing-E_T
channel at Run I. We provide predictions for signatures expected by the model
at Run II.Comment: 23 pages, Latex file + 10 figures and 4 Tables (included) Includes
JHEP3.cls and axodraw.st
Physics at high Q^2 and p^2_t: Summary of DIS 2000
We summarize the experimental and theoretical results presented in the
"Physics at the Highest Q^2 and p^2_t" working group at the DIS 2000 Workshop.
High Q^2 and p^2_t processes measured at current and future colliders allow to
improve our knowledge of Standard Model (SM) physics, by providing precise
measurements of the SM parameters and, consequently, consistency checks of the
SM. Moreover, they give information on key quantities for the calculation of
the SM expectations in a yet unexplored domain, such as the parton densities of
the proton or the photon. In addition to these experimental inputs,
higher-order calculations are also needed to obtain precise expectations for SM
processes, which are a key ingredient for the searches for new phenomena in
high Q^2 and p^2_t processes at current and future experiments. The
experimental and theoretical status of SM physics at high Q^2 and p^2_t is
reviewed in the first part of this summary, with the remaining being dedicated
to physics beyond the Standard Model.Comment: 17 pages, 10 figures. Typos correcte
Small scale structure predictions from discrete symmetry breaking: early quasar formation
We discuss the local density fluctuations which arise due to the topological defects that appear after the phase transition of light pseudo-Goldstone bosons. It has been found that in a post-inflationary universe the fluctuations of these defects at large scales may have led to galaxy formation, while being consistent with the measurements of the cosmic microwave background radiation. Here we show that, at the local level, the same fluctuations may be sufficiently large to lead to the production of smaller structures (ie quasars) with the observed distribution, which peaks at z=2 and drops rapidly for higher redshifts. Moreover it may be possible that a limited number of quasars are produced at redshifts of order 10, much earlier than what hot and cold dark matter scenarios predict. Although in this letter we work in the parameter space which is optimal for the generation of large scale structure as well, these features are generic for a wide class of domain wall models
PHASE TRANSITION OF N-COMPONENT SUPERCONDUCTORS
We investigate the phase transition in the three-dimensional abelian Higgs
model for N complex scalar fields, using the gauge-invariant average action
\Gamma_{k}. The dependence of \Gamma_{k} on the effective infra-red cut-off k
is described by a non-perturbative flow equation. The transition turns out to
be first- or second-order, depending on the ratio between scalar and gauge
coupling. We look at the fixed points of the theory for various N and compute
the critical exponents of the model. Comparison with results from the
\epsilon-expansion shows a rather poor convergence for \epsilon=1 even for
large N. This is in contrast to the surprisingly good results of the
\epsilon-expansion for pure scalar theories. Our results suggest the existence
of a parameter range with a second-order transition for all N, including the
case of the superconductor phase transition for N=1.Comment: 30p. with 9 uuencoded .eps-figures appended, LaTe
Direct T-violation measurements and T-odd effects in decay experiments
Motivated by the recent experimental announcements for direct measurements of
time-reversal non-invariance in the neutral kaon system, we make a comparative
discussion of the CPLEAR and KTeV measurements. The most suitable way to
consistently incorporate the mixing, the time evolution and the decays of
kaons, is to describe the neutral kaon system as a system with a non-Hermitean
Hamiltonian. In this framework, the physical (decaying) incoming and outgoing
states are distinct and belong to dual spaces. Moreover, since they are
eigenstates of the full Hamiltonian, they never oscillate. This is directly
manifest in the orthogonality conditions of the physical states, which entirely
determine the evolution of the kaon system. Along these lines we conclude:
CPLEAR studies K0-bar{K0} oscillations, a process where initial and final
states can be reversed, the CPLEAR asymmetry being an effect directly related
to the definition of time-reversal. Conclusively, CPLEAR provides a direct
measurement of T-violation without any assumption either on unitarity or on
CPT-invariance. The KTeV experiment studies in particular the process KL -> pi+
pi- e+ e- where they measure a T-odd effect. However, using unitarity together
with estimates of the final state interactions, it should be possible to
determine whether this effect can be identified with a genuine T-reversal
violation.Comment: 11 pages, no figures. Presented at the 34th Rencontres de Moriond on
Electroweak Interactions and Unified Theories, Les Arcs, 13-20 March, 199
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