M. Ramón Medrano

Role of sterile neutrino warm dark matter in rhenium and tritium beta decays

Abstract Sterile neutrinos with mass in the range of one to a few keV are important as extensions of the Standard Model of particle physics and are serious dark matter (DM) candidates. This DM mass scale (warm DM) is in agreement with both cosmological and galactic observations. We study the role of a keV sterile neutrino through its mixing with a light active neutrino in rhenium 187 and tritium beta decays. We pinpoint the energy spectrum of the beta particle, 0 ≲ T e ≲ ( Q β − m s ) , as the region where a sterile neutrino could be detected and where its mass m s could be measured. This energy region is at least 1 keV away from the region suitable to measure the mass of the light active neutrino, located near the endpoint Q β . The emission of a keV sterile neutrino in a beta decay could show up as a small kink in the spectrum of the emitted beta particle. With this in view, we perform a careful calculation of the rhenium and tritium beta spectra and estimate the size of this perturbation by means of the dimensionless ratio R of the sterile neutrino to the active neutrino contributions. We comment on the possibility of searching for sterile neutrino signatures in two experiments which are currently running at present, MARE and KATRIN, focused on the rhenium 187 and tritium beta decays respectively.

Classical splitting of fundamental strings.

We find exact solutions of the string equations of motion and constraints describing the classical splitting of a string in two. We show that for the same Cauchy data the strings that split have a smaller action than the string without splitting. This phenomenon is already present in flat space-time. The mass, energy, and momentum carried out by the strings are computed. We show that the splitting solution describes a natural decay process of one string of mass M into two strings with a smaller total mass and some kinetic energy. The standard nonsplitting solution is contained as a particular case. We also describe the splitting of a closed string in the background of a singular gravitational plane wave, and show how the presence of the strong gravitational field increases (and amplifies by an overall factor) the negative difference between the action of the splitting and nonsplitting solutions.

Towards a realistic supersymmetric SU8 model

Abstract Flavour superunification is accomplished via a SU 8 supersymmetric model, free of anomalies, asymptotically free, and with three families of light fermions, through a SU 8 → SU 5 → SU 3 × SU 2 × U 1 breaking. Possible patterns of supersymmetry breaking are described.

The general solution of the 2D sigma model stringy black hole and the massless complex sine-Gordon model

Abstract The exact general solution for a sigma model having the 2D stringy black hole (SBH) as internal manifold is found in closed form. We also give the exact solution for the massless complex sine-Gordon (MCSG) model. Both, models and their solutions are related by analytic continuation. The solution is expressed in terms of four arbitrary functions of one variable.

Spontaneously broken supersymmetric models free of fine-tuned parameters and ΔB, ΔL troubles (I). General survey

Abstract We propose a class of supersymmetric models based on canonical U( n ) gauge groups with the following properties: (i) absence of anomalies; (ii) no quadratic renormalizations for the D terms; (iii) absence of fine-tuned parameters; (iv) spontaneous SUSY breaking a la Fayet-Iliopoulos; (v) free of unobserved effective ΔB ≠ 0 and ΔL ≠ 0 interactions.

Boson-fermion and fermion-boson transmutations induced by supergravity backgrounds in superstring theory

Abstract We investigate the physical implications and particle content of superstring scattering in the supergravity shock-wave background recently found by us. The amplitudes for the different particle transmutation processes taking place in this geometry are explicitly computed for Gree-Schwarz superstring, including the new phenomena of fermion to boson and boson to fermion transmutations. Transition amplitudes among the ground states, first and second excited states are obtained. Particularly interesting are the amplitudes within the massless particle sector, which lead to physical massive particles upon supersymmetry breaking at low energies.

THE SL(2,R) WZWN STRING MODEL AS A DEFORMED OSCILLATOR AND ITS CLASSICAL-QUANTUM STRING REGIMES

We study the SL(2,R) WZWN string model describing bosonic string theory in AdS3 spacetime as a deformed oscillator together with its mass spectrum and the string modified SL(2,R) uncertainty relation. The SL(2,R) string oscillator is far more quantum (with higher quantum uncertainty) and more excited than the non-deformed one. This is accompassed by the highly excited string mass spectrum which is drastically changed with respect to the low excited one. The highly excited quantum string regime and the low excited semiclassical regime of the SL(2,R) string model are described and shown to be the quantum-classical dual of each other in the precise sense of the usual classical-quantum duality. This classical-quantum realization is not assumed nor conjectured. The quantum regime (high curvature) displays a modified Heisenbergs uncertainty relation, while the classical (low curvature) regime has the usual quantum mechanics uncertainty principle.

SEMICLASSICAL (QFT) AND QUANTUM (STRING) ANTI-DE SITTER REGIMES: NEW RESULTS

We compute the quantum string entropy Ss(m, H) from the microscopic string density of states ρs(m, H) of mass m in Anti-de Sitter space–time. For high m, (high Hm → c/α′), no phase transition occurs at the Anti-de Sitter string temperature Ts = (1/2πkB)Lclc2/α′, which is higher than the flat space (Hagedorn) temperature ts. (Lcl = c/H, the Hubble constant H acts as producing a smaller string constant α′ and thus, a higher tension). Ts is the precise quantum dual of the semiclassical (QFT) Anti-de Sitter temperature scale Tsem = ℏc/(2πkBLcl). We compute the quantum string emission σstring by a black hole in Anti-de Sitter (or asymptotically Anti-de Sitter) space–time (bhAdS). For Tsem bhAdS ≪ Ts (early evaporation stage), it shows the QFT Hawking emission with temperature Tsem bhAdS (semiclassical regime). For Tsem bhAdS → Ts, it exhibits a phase transition into a Anti-de Sitter string state of size , and Anti-de Sitter string temperature Ts. New string bounds on the black hole emerge in the bhAdS string regime. The bhAdS string regime determines a maximal value for H : Hmax = 0.841c/ls. The minimal black hole radius in Anti-de Sitter space–time turns out to be rg min = 0.841ls, and is larger than the minimal black hole radius in de Sitter space–time by a numerical factor equal to 2.304. We find a new formula for the full AdS entropy Ssem(H), as a function of the usual Bekenstein–Hawking entropy . For Lcl ≫ lPlanck, i.e. for low H ≪ c/lPlanck, or classical regime, is the leading term with its logarithmic correction, but for high H ≥ c/lPlanck or quantum regime, no phase transition operates, in contrast to de Sitter space, and the entropy Ssem(H) is very different from the Bekenstein–Hawking term .

SEMICLASSICAL (QFT) AND QUANTUM (STRING) ROTATING BLACK HOLES AND THEIR EVAPORATION: NEW RESULTS

Combination of both quantum field theory (QFT) and string theory in curved backgrounds in a consistent framework, the string analogue model, allows us to provide a full picture of the Kerr–Newman black hole and its evaporation going beyond the current picture. We compute the quantum emission cross-section of strings by a Kerr–Newman black hole (KNbh). It shows the black hole emission at the Hawking temperature Tsem in the early stage of evaporation and the new string emission featuring a Hagedorn transition into a string state of temperature Ts at the last stages. New bounds on J and Q emerge in the quantum string regime (besides the known ones of the classical/semiclassical QFT regime). The last state of evaporation of a semiclassical Kerr–Newman black hole with mass M > mPl, angular momentum J and charge Q is a string state of temperature Ts, string mass Ms, J = 0 and Q = 0, decaying as usual quantum strings do into all kinds of particles. (Naturally, in this framework, there is no loss of information, ...

NEW DUAL RELATIONS BETWEEN QUANTUM FIELD THEORY AND STRING REGIMES IN CURVED BACKGROUNDS

A R “dual” transform is introduced which relates Quantum Field Theory and String regimesm, both in a curved background with D-non compact dimensions. This operation maps the characteristic length of one regime into the other (and, as a consequence, mass domains as well). The R-transform is not an assumed or a priori imposed symmetry but is revealed by the QFT and String dynamics in curved backgrounds. The Hawking-Gibbons temperature and the string maximal or critical temperature are R-mapped one into the other. If hack reaction of quantum matter is included, Quantum Field Theory and String phases appear, and R-relations between them manifest as well. T hese R-transformations are explicitly shown in two relevant examples: Black Hole and de Sit ter space times.