Jorge L. Lopez

Astrophysical constraints on massive unstable neutral relic particles

Abstract There has recently been renewed interest in massive neutral dark-matter particle candidates with masses greater than ∼ 1 TeV which may be unstable. We re-evaluate the constraints on such particles from the possible effects of their decays on the spectrum of the microwave background-radiation and the primordially synthesised abundances of the light elements, from observations of the diffuse gamma-ray background radiation, and from searches for muons and neutrinos in nucleon-decay and cosmic-ray detectors. We find that such unstable neutral relics may well have the cosmological critical density if their lifetime exceeds ∼ 1016 yr. We illustrate our arguments by applying them to technicolour baryons and to “cryptons” in superstring-inspired models.

The search for a realistic flipped SU(5) string model

Abstract We present an extensive search for a class of flipped SU(5) models built within the free fermionic formulation of the heterotic string. We describe a set of algorithms which constitute the basis for a computer program capable of generating systematically the massless spectrum and the superpotential of all possible models within the class we consider. Our search through the huge parameter space to be explored is simplified considerably by the constraint of N = 1 spacetime supersymmetry and the need for extra Q, Q representations beyond the standard ones in order to possibly achieve string gauge coupling unification at scales of O(10 18 GeV). Our results are remarkably simple and evidence the large degree of redundancy in this kind of constructions. We find one model with gauge group SU (5)× U (1) Y × SO (10) h × SU (4) h × U (1) 5 and fairly acceptable phenomenological properties. We study the D- and F-flatness constraints and the symmetry breaking pattern in this model and conclude that string gauge coupling unification is quite possible.

Large (g-2) micro in SU(5) x U(1) supergravity models.

We compute the supersymmetric contribution to the anomalous magnetic moment of the muon within the context of

Precision tests of CPT symmetry and quantum mechanics in the neutral kaon system

SU(5)\times U(1)

Calculable Nonrenormalizable Terms in String Theory: A Guide for the Practitioner

supergravity models. The largest possible contributions to

Upper bounds on Higgs and top quark masses in the flipped SU(5)×U(1) superstring model

a^{susy}_\mu

New supersymmetric contributions tot→cV

occur for the largest allowed values of

Decisive role of nonrenormalizable terms in the flipped string

\tan\beta

Nonrenormalizable terms in the free fermionic formulation of 4D strings

and can easily exceed the present experimentally allowed range, even after the LEP lower bounds on the sparticle masses are imposed. Such

Tests of CPT symmetry and quantum mechanics with experimental data from CPLEAR

\tan\beta