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

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