arXiv subjects

Andre de Gouvea

Publications and source records attributed to Andre de Gouvea.

60 records · Page 4Linked to original sources

arXiv1998

Establishing a nu_{mu,tau} Component in the Solar Neutrino Flux

We point out that the recoil electron kinetic energy spectra in the nu-e elastic scattering are different for incident nu_{e} or nu_{mu,tau}, and hence one can in principle establish the existence of the nu_{mu,tau} component in the solar neutrino flux by fitting the shape of the spectrum. This would be a new model-independent test of the solar neutrino oscillation in a single experiment, free from astrophysical and nuclear physics uncertainties. For the ^7Be neutrinos, it is possible to determine the nu_{mu,tau} component at BOREXINO or KamLAND, if the background is sufficiently low. Note that this effect is different from the distortion in the incident neutrino energy spectrum, which has been discussed in the literature.

hep-ph↗

arXiv1998

Seiberg Duality and e+ e- Experiments

Seiberg duality in supersymmetric gauge theories is the claim that two different theories describe the same physics in the infrared limit. However, one cannot easily work out physical quantities in strongly coupled theories and hence it has been difficult to compare the physics of the electric and magnetic theories. In order to gain more insight into the equivalence of two theories, we study the ``e+ e-'' cross sections into ``hadrons'' for both theories in the superconformal window. We describe a technique which allows us to compute the cross sections exactly in the infrared limit. They are indeed equal in the low-energy limit and the equality is guaranteed because of the anomaly matching condition. The ultraviolet behavior of the total ``e+ e-'' cross section is different for the two theories. We comment on proposed non-supersymmetric dualities. We also analyze the agreement of the ``γγ'' and ``WW'' scattering amplitudes in both theories, and in particular try to understand if their equivalence can be explained by the anomaly matching condition.

hep-th↗

arXiv1998

Less Minimal Supersymmetric Standard Model

Most of the phenomenological studies of supersymmetry have been carried out using the so-called minimal supergravity scenario, where one assumes a universal scalar mass, gaugino mass, and trilinear coupling at M_{GUT}. Even though this is a useful simplifying assumption for phenomenological analyses, it is rather too restrictive to accommodate a large variety of phenomenological possibilities. It predicts, among other things, that the lightest supersymmetric particle (LSP) is an almost pure B-ino, and that the mu-parameter is larger than the masses of the SU(2)_{L} and U(1)_{Y} gauginos. We extend the minimal supergravity framework by introducing one extra parameter: the Fayet--Iliopoulos D-term for the hypercharge U(1), D_Y. Allowing for this extra parameter, we find a much more diverse phenomenology, where the LSP is \tildeν_τ, \tildeτ or a neutralino with a large higgsino content. We discuss the relevance of the different possibilities to collider signatures. The same type of extension can be done to models with the gauge mediation of supersymmetry breaking. We argue that it is not wise to impose cosmological constraints on the parameter space.

hep-ph↗

arXiv1997

Next-to-Minimal Supersymmetric Standard Model with the Gauge Mediation of Supersymmetry Breaking

We study the Next-to-Minimal Supersymmetric Standard Model (NMSSM) as the simplest candidate solution to the $μ$-problem in the context of the gauge mediation of supersymmetry breaking (GMSB). We first review various proposals to solve the $μ$-problem in models with the GMSB. We find none of them entirely satisfactory and point out that many of the scenarios still lack quantitative studies, and motivate the NMSSM as the simplest possible solution. We then study the situation in the Minimal Supersymmetric Standard Model (MSSM) with the GMSB and find that an order 10% cancellation is necessary between the $μ$-parameter and the soft SUSY-breaking parameters to correctly reproduce $M_Z$. Unfortunately, the NMSSM does not to give a phenomenologically viable solution to the $μ$-problem. We present quantitative arguments which apply both for the low-energy and high-energy GMSB and prove that the NMSSM does not work for either case. Possible modifications to the NMSSM are then discussed. The NMSSM with additional vector-like quarks works phenomenologically, but requires an order a few percent cancellation among parameters. We point out that this cancellation has the same origin as the cancellation required in the MSSM.

hep-ph↗

arXiv1997

Excluding Light Gluinos from Z decays

We reanalyze the constraints on light gluinos (m_{\tilde{g}}\leq 5 GeV/c^2) from the hadronic Z decays into four jets. We find that the published OPAL data from the 1991 and 1992 runs exclude a light quasi-stable gluino with mass \lesssim 1.5 GeV/c^2 at more than 90% confidence level. This limit depends little on assumptions about the gluino fragmentation and the definition of the gluino mass. The exclusion confidence level is shown as a function of the mass. A future projection is briefly discussed. We also discuss quantitatively how the distributions in the Bengtsson-Zerwas and the modified Nachtmann-Reiter angles change due to the finite bottom quark or gluino mass. The analysis is limited to the leading-order calculations. We, however, give an empirical reason to why the next-to-leading-order corrections are unlikely to change our conclusions.

hep-ph↗

arXiv1997

Cosmology of Supersymmetric Models with Low-energy Gauge Mediation

We study the cosmology of supersymmetric models in which the supersymmetry breaking effects are mediated by gauge interactions at about the 10^5 GeV scale. We first point out that the gravitino is likely to overclose the Universe in this class of models. This requires an entropy production, which prefers a baryogenesis mechanism at a relatively low temperature. The Affleck-Dine mechanism for baryogenesis is one of the possibilities to generate enough baryon asymmetry, but the analysis is non-trivial since the shape of the potential for the flat direction differs substantially from the conventional hidden sector case. To see this, we first perform a 2-loop calculation to determine the shape of the potential. By combining the potential with the supergravity contribution, we then find that the Affleck-Dine baryogenesis works efficiently to generate sufficient baryon asymmetry. On the other hand, we also point out that string moduli fields, if present, are stable and their coherent oscillations overclose the Universe by more than 15 orders of magnitude. One needs a very late inflationary period with an e-folding of N \gtrsim 5 and an energy density of \lesssim (10^7 GeV)^4. A thermal inflation is enough for this purpose. Fortunately, the Affleck-Dine baryogenesis is so efficient that enough baryon asymmetry can survive the late inflation.

hep-ph↗