8a Trobada de Nadal de Física Teòrica a la Universitat de Barcelona

Dies: 17 i 18 de desembre de 2008
Lloc: Antiga Sala de Graus (A 01 S) Facultat de Fisica de la Universitat de Barcelona

Tomeu Fiol & David Mateos
bfiolub.edu

Programa

Programa 17 de Desembre

Programa 18 de Desembre

Abstracts

Dimecres, 17 de Desembre

Dijous, 18 de Desembre

Santi Béjar (MPI, Munich)

"The W h0 decay mode of the charged Higgs boson in the MSSM: a complete 1-loop analysis "

We analyze the full one loop computation of the decay of the charged Higgs boson into a W-boson and a light CP-even neutral Higgs boson, H+ -> W h0, at order O((\alpha_ew)^2,\alpha_ew \alpha). We explore the behavior of the width in several phenomenologically well-motivated scenarios (maximum M_h0, no-mixing, small \alpha_eff) and obtain large radiative corrections (typically 50 -100 %). Eventually quantum corrections can be even larger, signaling that the decay takes place virtually through a loop-induced mechanism. These enhancements can be traced back to the vertex corrections involving top quarks/squarks and bottom quarks/squarks, as well as to the wave-function corrections coming from the h0 - H0 mixing.

Oscar Catà (Berkeley, USA)

" \alpha_s from tau decay: still room for improvements? "

Tau decay based analyses provide the most accurate determinations of the strong coupling constant to date. In the last year, recent tau data from the ALEPH collaboration prompted new determinations of $\alpha_s$ which show some tension at the 1-2 sigma level. While these discrepancies may well be due to underestimation of errors, they could also be the effect of non-perturbative physics beyond the OPE. These extra non-perturbative contributions, collected under the name of duality violations, are normally deemed negligible, but little effort has been devoted to evaluate their actual size directly from data. In this talk I will report on a new analysis in which we explored the size of duality violations supported by tau data. Our conclusion is that there is a potential effect in $\alpha_s$ as big as the theoretical uncertainty quoted in previous analyses.

Francesc Ferrer (Washington U., USA)

" Antimatter, nonperturbative field configurations and magnetic fields"

Observations of the Milky Way by the SPI/INTEGRAL satellite reveal the presence of a strong 511 KeV gamma-ray line emission from the bulge. These observations are hard to account for by conventional astrophysical scenarios, whereas other proposals, such as light DM, face stringent constraints from the diffuse gamma-ray background. I will describe how light superconducting strings could be the source of the observed 511 KeV emission. The associated particle physics, at the ~ 1 TeV scale, is within reach of planned accelerator experiments, while the scenario has a distinguishing spatial distribution, proportional to the galactic magnetic field. I will also discuss how cosmic magnetic fields of nano-Gauss strength today could have been created at the time of baryogenesis. In addition to being astrophysically relevant, such magnetic fields, which are helical, can provide an independent probe of baryogenesis and CP violation in particle physics.

Xavier Garcia i Tormo (Argonne National Laboratory, USA)

"Update on the QCD static potential perturbative calculations "

I will review the current status of the perturbative calculations for the QCD potential between a static quark and antiquark. A comparison with lattice data will also be presented.

Sean Hartnoll (Harvard, USA)

" Holographic Superconductors"

I will review recent progress on building a gravitational dual, in the sense of AdS/CFT, for superconducting systems.

Federico Mescia (INFN Frascati, Italy)

"Recent Progress on Flavour Physics"

I will present a summary of what we learned so far from low-energy flavour-quark observables, concerning physics beyond the Standard Model (SM). In the last few years there has been a great experimental progress in quark and lepton flavour physics. In the quark sector, the validity of the SM has been strongly reinforced by a series of challenging tests. More important, several suppressed observables (such as DMBs, sin(2beta), epsK, b->sgamma) potentially sensitive to New Physics (NP) have been measured with good accuracy, showing no deviations from the SM. In constructing a realistic SM extension we should then try to reconcile many non-trivial constraints. The Minimal Flavour Violation hypothesis well handles flavour-quark data and shows, in the large tanbeta scenario, interesting effects to be detected by Lhcb.

Juan Rojo (INFN, Italy)

" (Neural Network) Parton Distributions for precision LHC physics "

A detailed knowledge of parton distributions and their associated uncertainties is of paramount importance for the full exploitation of the LHC physics potential. The standard approach to PDF determination, however, suffers from several drawbacks, related to the lack of control on the bias introduced in the choices of specific PDF parametrizations and flavour assumptions, as well as to the difficulty in providing a consistent statistical interpretation of PDFs uncertainties in the presence of incompatible data. We present an alternative strategy to PDF determination, the NNPDF approach, based on a combination a Monte Carlo sampling of experimental data with neural networks as unbiased interpolators for the PDFs parametrization which overcomes those drawbacks. We discuss the present status of the NNPDF analysis and discuss implications for LHC physics.

Miquel Tierz, (Brandeis, USA)

"Quantum topology and strongly-correlated systems: the Chern-Simons model "

We introduce and study the main features of a 1D exactly solvable model derived in Chern-Simons theory. The model inherits the quantum topological invariants delivered by Chern-Simons theory and, in addition, is intimately related to several long-standing models in condensed matter physics: 1) the Calogero-Sutherland model and the low-energy ground state wavefunction of a Luttinger liquid, 2) the Laughlin wavefunction on a cylinder and 3) a charged Bose gas in 1D that extends the Lieb-Liniger model.