New Parametrizations for the Photon Structure Function

In the last year four new parametrizations of the Hadronic Photon Structure Function at Next to Leading Order have appeared. In this talk, I briefly review the main features of three of them: the FFNS_CJK, CJK and AFG.Comment: 7 pages, 2 figures. Talk presented at the Photon 2005 Conference, Warsaw (Poland

Physics Beyond the Standard Model at HERA

This talk is divided in two parts. In the first one we discuss the signals of the Minimal Supersymmetric Standard Model through the production of \tilde{e} \tilde{q}. The second part is devoted to contact terms. The bounds on the mass scale Lambda obtained from atomic parity violation experiments and from LEP are reviewed. Afterwards, we show that the excess of events at high Q^2 observed at HERA could be explained in terms of these contact terms.Comment: 15 pages. LaTeX2e, 3 Postscript figures included. Talk presented by F. Cornet at the XXI International School on Theoretical Physics, Ustron (Poland), September 1997. To appear in Acta Physica Polonica

Tests of Chiral Perturbation Theory at DAΦNE

Presented at the XXIII International School of Theoretical Physics "Recent Development in Theory of Fundamental Interactions" Ustrón. Poland, september 15-22, 1999.DAΦNE will offer an opportunity to check Chiral Perturbation Theory predictions at higher order. In this talk I have selected a few topics for which it is expected that the lowest order calculation will not be sufficient in order to compare with the experimental results. In particular I will discuss pion pair production in two photon collisions, Kl3 and Kl4 decays.This work has been partially supported by the EEC, TMR-CT98-0169 (EU-RODAPHNE network), CICYT, under contract AEN96-1672 and Junta de Andalucía, under contract FQM101

New parametrizations for the photon structure function

Presented at the PHOTON2005 Conference, 31 August–4 September, 2005, Warsaw, Poland.In the last year four new parametrizations of the Hadronic Photon Structure Function at Next to Leading Order have appeared. In this talk, I briefly review the main features of the three of them: the FFNSCJK, CJK and AFG.This work has been partially supported by Junta de Andalucia (contract FQM-330), Ministerio de educación y Ciencia (contract FPA2003-09298-c02-01) and the European Community’s Human Potential Programme (contract HPRN-CT-2002-00311 EURIDICE)

Photoproduction with a mini-jet model and Cosmic Ray showers

We present post-LHC updates of estimates of the total photo-production cross section in a mini-jet model with infrared soft gluon resummation, and apply the model to study Cosmic Ray shower development, comparing the results with those obtained from other existing models.Comment: 7 pages, 5 figures, presented at Photon 2017, 22-26 May 2017 CER

Spin dependence of heavy quark fragmentation

We propose that the non-perturbative part of the fragmentation function describing the transition from a heavy quark to a heavy meson is proportional to the square of the produced meson wave function at the origin, taking into account hyperfine interactions. We analyze the effects of this proposal on the number of pseudoscalar mesons compared to the number of vector mesons produced and find a good agreement with experimental data. Finally, we discuss further experimental checks for our hypothesis.Facultad de Ciencias Exacta

Controlled Flavour Changing Neutral Couplings in Two Higgs Doublet Models

We propose a class of Two Higgs Doublet Models where there are Flavour Changing Neutral Currents (FCNC) at tree level, but under control due to the introduction of a discrete symmetry in the full Lagrangian. It is shown that in this class of models, one can have simultaneously FCNC in the up and down sectors, in contrast to the situation encountered in BGL models. The intensity of FCNC is analysed and it is shown that in this class of models one can respect all the strong constraints from experiment without unnatural fine-tuning. It is pointed out that the additional sources of flavour and CP violation are such that they can enhance significantly the generation of the Baryon Asymmetry of the Universe, with respect to the Standard Model.Comment: 29 pages, 3 figure

Physics beyond the standard model at hera

This talk is divided in two parts. In the first one we discuss the signals of the Minimal Supersymmetric Standard Model through the production of eq. The second part is devoted to contact terms. The bounds on the mass scale A obtained from atomic parity violation experiments and from LEP are reviewed. Afterwards, we show that the excess of events at high Q-2 observed at HERA could be explained in terms of these contact terms.This work was partially supported by CICYT under contract AEN96-1672 and by Junta de Andalucía