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(Last Modified on 27 Dec 2003)

UPCOMING SEMINARS

TBA.
M. Plumacher (CERN)
July 25, Fri.
Abstract: TBA
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Cosmological vacuum energy, black holes and CMBR in the microscopic theory of gravitation.
Pawel Mazur (South Carolina U.)
July 17, Thu. *Location U.B.* (joint seminar UB-UAB).
Abstract:
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TBA.
Frank Kruger
June 27, Fri.
Abstract:
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TBA.
S. Palomares (U. Valencia)
June 13, Fri.
Abstract:
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Real clocks and the Zeno effect.
I. Egusquiza (U. Pais Basc)
June 6, Fri.
Abstract:
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Mimicking Transplanckian effects in the CMB with conventional physics
Jim Cline (McGill U., Montreal)
June 2, Mon.
Abstract: We investigate the possibility that fields coupled to the inflaton can influence the primordial spectrum of density perturbations through their coherent motion. For example, the second field in hybrid inflation might be oscillating at the beginning of inflation rather than at the minimum of its potential. Although this effect is washed out if inflation lasts long enough, we note that there can be up to 30 e-foldings of inflation prior to horizon crossing of COBE fluctuations while still giving a potentially visible distortion. Such pumping of the inflaton fluctuations by purely conventional physics can resemble transPlanckian effects which have been widely discussed. The distortions which they make to the CMB could leave a distinctive signature which differs from generic effects like tilting of the spectrum.
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Non leptonic kaon decay
Maarten Golterman (San Francisco)
May 30, Fri.
Abstract:
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Brane Worlds and Non-Conformal Dual Theories
Tony Gherghetta (Minnesota)
May 23, Fri.
Abstract: The supergravity dual descriptions of non-conformal super Yang-Mills theories realized on the world-volume of Dp-branes are used to compute the stress-energy tensor and vector current correlators. These results are then applied to the study of dilatonic brane-worlds which are described by non-conformal field theories coupled to gravity. It is found that brane-worlds based on D4 and D5 brane solutions exhibit a localization of gauge and gravitational fields, and the corrections to the Newton and Coulomb laws can be calculated in these theories.
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Physics with forward protons at hadron colliders.
V. Khoze (Durham Univ.)
May 16, Fri.
Abstract:
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The Cosmological Constant Problem
Stefan Nobbenhuis (Utrecht)
May 9, Fri.
Abstract: The talk is intended to bring some order in the chaos of ideas surrounding the Cosmological Constant Problem. After briefly reviewing the main lines of thought I will delve deeper into what appear to be the most important roads towards a deeper understanding. As a starter I will discuss a symmetry principle keeping a static Cosmological Constant small. This is generally regarded as the most elegant but also most difficult approach, with a very nice idea by Gerard 't Hooft and thoughts on (unbroken) supersymmetry. Then I will focus on a dynamical Cosmological Constant, especially paying attention to back-reaction and instabilities in de Sitter space. There are many other dynamical approaches besides the ones mentioned, but they appear to be objectionable, as I shall try to demonstrate.
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Neutrino oscillations in dense neutrino media
Sergio Pastor (IFIC/Univ. Valencia)
May 6, Tue.
Abstract: In the early universe or in some regions of supernovae, the neutrino refractive index is dominated by the neutrinos themselves. Several previous studies found numerically that these self-interactions have the effect of coupling different neutrino modes in such a way as to synchronize the flavour oscillations which otherwise would depend on the energy of a given mode. We show a simple explanation for this baffling phenomenon in analogy to the weak-field Zeeman effect in atoms. As applications, we discuss flavour neutrino oscillations in the early universe with non-zero neutrino asymmetries and in the rarefied region just outside the nascent neutron star a few seconds after supernova bounce.
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DIS semi-inclusivo y QCD: Funciones de Fractura
C. Garcia Canal (U. de la Plata, Argentina).
May 5, Mon. at 12:00 (Notice different time)
Abstract: Se analizan las correcciones perturbativas de QCD a la dispersion profundamente inelastica semi-inclusiva, en orden siguiente al dominante. Se destaca el papel fundamental jugado por las funciones de fractura, ligadas a los procesos de fragmentacion en el blanco, en relacion con la factorizacion de las singularidades colineales. Se cuantifican los efectos de la evolucion no homogenea de estas funciones.
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One-dimensional Quantum wires
Alberto Rodriguez (U. Salamanca and UAB)
April 30, Wed.
Abstract: We propose a model of one dimensional wires consisting of an array of delta potentials. The main physical motivation is to modelate quantum wire band structure and the calculation of the associated density of states. These quantities show the fundamental properties one expects in the case of a periodic structure. When disorder is present we find Anderson localization and clear signals of fractality in the distribution of states. It is also established how due to the presence of correlations in the disorder the density of states is essentially modified and the localization of the electronic states changes in a non negligible proportion which might alter some macroscopic properties of these structures. In spite of the simplicity of the model some interesting and novel properties arise.
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Quantum self-consistent Ads x Sigma brane models
Antonino Flachi
April 25, Fri.
Abstract: We consider a class of higher dimensional brane models with the topology of AdS x (Compact Manifold) and study how such models resolve the gauge hierarchy between the Planck and electroweak scales with the help of quantum effects. We also address the self-consistency of the solution and prove that the classical brane solution is not spoiled at the quantum level.
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Renormalization and Unification in RS1
Antonio Delgado (Johns Hopkins)
April 8,Tues.
Abstract: We study unification in the Randall-Sundrum scenario for solving the hierarchy problem, with gauge fields and fermions in the bulk. We calculate the one-loop corrected low-energy effective gauge couplings in a unified theory, broken at the scale M_GUT in the bulk. We find that, although this scenario has an extra dimension, there is a robust (calculable in the effective field theory) logarithmic dependence on M_GUT, strongly suggestive of high-scale unification, very much as in the (4D) Standard Model. Moreover, bulk threshold effects are naturally small, but volume-enhanced, so that we can accommodate the measured gauge couplings. A 4D dual interpretation, in the sense of the AdS/CFT correspondence, is provided for all our results.
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The debate on galaxy space distribution
Marco Montuori (U. Roma "La sapienza")
April 4,Fri.
Abstract: A critical assumption of the hot big bang model is that matter is uniformely distributed in space beyond a certain scale. The most direct check in this respect is the statistical analysis of the three dimensional distribution of galaxies in space. In the last 25 years much effort of current research has been devoted to such issue, with the discovery of large and really unexpected inhomogeneities in the luminous matter distribution. Up to now there is no clear identification of the homogeneity scale in galaxy space distribution. Here I will review the current debate on this topic showing the very recent results of new galaxy catalog analysis.
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Power-Law Effects in Extra-Dimensional Unified Models
Arthur Hebecker (DESY)
March 28, Fri.
Abstract: Extra dimensions allow for a very simple and phenomenologically successful realization of the idea of Grand Unification. This is linked to the possible symmetry breaking at the boundaries of the extra-dimensional space. If, in addition to the boundary breaking, the unified gauge symmetry is also broken by the vacuum expectation value of a scalar bulk field, power-like loop corrections to gauge coupling unification can arise. I will discuss the calculability of these power-like threshold corrections and show that, in some of the simplest and most attractive settings, they can be quantitatively analyzed within the framework of effective field theory.
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Neutrino masses: a theorist's perspective
Francesca Borzumati (IFAE)
March 24, Mon.
Abstract: Implications of nonvanishing neutrino masses for physics beyond the SM, in particular susy models with and without Rparity, are discussed. Emphasys is given to the size of scales needed to accommodate very light and possibly sterile neutrinos.
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Recent developments in inflationary cosmology
Antonio Riotto (Univ. of Padua)
March 12
Abstract: We will discuss some recent theoretical and observational developments in cosmology with particular emphasis on the new informations provided by the Wilkinson Microwave Anistropy Probe (WMAP) experiment and its impact on the inflationary paradigm.
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Inclusive rare B decays
Christoph Greub (University of Bern)
March 4
Abstract: First, I will report on the NLL QCD corrections to B-> X_s gamma in the Standard model and also briefly on an important class of NNLL corrections to this process, which were recently worked out. Second, I will discuss the analogous SM contributions to the branching ratio and the forward-backward asymmetry in B-> X_s l^+ l^- (l= muon or electron). Third, if time allows, I will briefly comment on a model indep. analysis of the Wilson coeff. C_7, C_8, C_9 and C_10.
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An orbifold SO(10) GUT in 6D
Laura Covi (DESY)
February 28
Abstract: We describe a supersymmetric SO(10) GUT in six dimensions broken by orbifolding to the supersymmetric Standard Model with an additional U(1) in four dimensions. We discuss general anomaly constraints on such kind of models and give a general expression for bulk and brane anomalies depending on the orbifold parities. Then we present a particular realization, that contains the Higgs fields which are needed to break the electroweak and ${B-L}$ gauge symmetries, and matter fields to generate quark mixing and neutrino masses via the seesaw mechanism.
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Recent WMAP results and particle physics
Pasquale di Bari (IFAE/UAB)
February 21
Abstract: We will report on the recent results from the WMAP experiment that measured the CMB temperature anisotropies on the full sky with a 30 times finer resolution than the previous COBE experiment. These observations made it possible to measure many cosmological parameters with a highly improved precision. We will mainly focus on the impact of such results on fundamental physics, discussing in particular the new information on inflationary models with some claimed "intriguing discrepancies" and hints of small deviations from Standard Big Bang Nucleosynthesis.
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Light mesons from unitarized Chiral perturbation theory
J.R. Pelaez (Univ. Florencia, Univ. Complutense de Madrid)
February 14
Abstract:
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Holographic phenomenology
Roberto Contino, Universidad Autonoma de Madrid
February 7
Abstract: Randall-Sundrum scenarios with gauge vectors in the bulk admit a remarkable interpretation in terms of a 4d "holographic" theory. Depending on the boundary conditions assigned to the gauge fields, different patterns of global and local symmetries emerge in the holographic theory. I will discuss some particularly interesting setups which could be relevant for Grand Unification and Electroweak Symmetry breaking.
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Topics in string cosmology
F. Quevedo (Cambridge University)
January 24
Abstract: The interaction of branes and antibranes provides a good scenario for the realisation of cosmological inflation with explicitly computable potentials from string theory. The ending of inflation is also provided by a stringy field: the open string tachyon. An overview is presented of these ideas including a discussion on the bound state of branes and antibranes (the `branonium') that has some surprisng properties.
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Neural network parametrization of deep-inelastic structure functions
José Ignacio Latorre (UB)
January 17
Abstract: Deep-inelastic structure functions are parametrized using a Monte Carlo generated ensemble of neural networks. This method provides an effective measure in the space of structure functions with a small bias that allows the handling of errors and their correlations.
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Violación de la desigualdad de Bell más allá del límite de Cirel'son
ADÁN CABELLO. Universidad de Sevilla.
January 13
Abstract: La desigualdad de Bell en la versión de Clauser, Horne, Shimony y Holt, establece que el valor absoluto de la suma de los resultados de ciertos experimentos separados por intervalos de género espacio sobre un sistema de dos partículas debe estar acotado por 2 en cualquier teoría de variables ocultas locales (en particular, en cualquier teoría con "elementos de realidad" como los definidos por Einstein, Podolsky y Rosen). Es bien sabido que ciertas predicciones de la mecánica cuántica violan esta limitación. Por otro lado, está muy extendida la opinión de que "Quantum theory does not allow any stronger violation of the CHSH inequality than the one already achieved in Aspect's experiment [2 \sqrt{2}]." (A. Peres, Quantum Theory: Concepts and Methods, p. 174.), o "The violation of the Bell inequality found in (...) [2 \sqrt{2}] is the maximum possible in quantum mechanics." (M. A. Nielsen and I. L. Chuang, Quantum Computation and Quantum Information, p. 118). El valor 2 \sqrt{2} se conoce como el límite de Cirel'son. Las predicciones de la mecánica cuántica para dos partículas extraídas de un sistema de tres partículas preparadas en determinados estados cuánticos violan la desigualdad de Bell-CHSH más allá del límite de Cirel'son.
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New results for weak decay form factors from QCD sum rules on the light-cone
P. Ball, University of Durham
December 12
Abstract: present new results for B->pi and B->rho decay form factors, which are very relevant for the analysis of data coming in from the B factories BaBar and Belle and for the precision determination of the CKM unitarity triangle. I also compare with results from alternative methods (perturbative QCD factorizatio, lattice) and stress the importance of combining different approaches.
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BRANE EFFECTS IN ORBIFOLD GAUGE THEORIES
M. Quiros, CSIC
November 29
Abstract: not available
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El sol, una estrella variable cerca de nosotros
Vicente Domingo (Univ. de València)
November 22
Abstract: Veremos algunos aspectos de la variabilidad del Sol, de cuyas causas y efectos ha habido avances importantes en su conocimiento en los últimos años. El campo magnético que reside la zona de convección y se manifiesta en la atmósfera solar aparece como el vehículo de las variaciones mas conspicuas. La actividad magnética induce la variación de la irradiancia total o constante solar, y de las diversas formas de actividad observadas en la atmósfera solar: manchas, fáculas, eyecciones de masa coronal, etc. Los mecanismos físicos que intervienen empiezan a ser identificados. Su relación con el ambiente terrestre será brevemente analizado.
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Dark Matter Detection in the Light of Recent Experimental Results
C. Muñoz (UAM)
October 18
Abstract: Recently, several experiments for the direct detection of dark matter have reported results. One of the collaborations actually claims that the first evidence for dark matter has already been observed, in particular in the form of Weakly Interacting Massive Particles (WIMPs). This issue will be discussed in this talk. After a brief introduction to dark matter, its direct detection through elastic scattering with nuclei in a material will be analyzed. Finally, whether or not the existing theoretical models (supersymmetry, superstrings) give rise to cross sections in the range where current dark matter detectors are sensitive, will be discussed in some detail.
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Large TeV scale Electroweak Interactions
Paolo Ciafaloni (INFN - Sezioni di Lecce)
October 11
Abstract: At energies $E$ much higher than the simmetry breaking scale $M_W\approx 100$ GeV, radiative electroweak corrections are enhanced by double logs $\log^2\frac{E}{M_W}$, related to the infrared structure of the theory. In contrast to what happens in QED and QCD, these double logs are present even for inclusive observables, leading to a violation of the Bloch-Nordsieck theorem. As a result, the cross section for $e^+ e^-\to$ hadrons is dominated by electroweak corrections which are twice as big as the QCD ones at the TeV scale. Quite in general, one loop EW corrections are in the $5-20$\% range at the TeV scale, so considering higher order corrections and/or all order resummation of leading terms is mandatory in some cases. I show how the resummation problem can be addressed through evolution equations similar to DGLAP equations in QCD; due to the presence of double logs new kinds of splitting functions have to be defined.
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Anomalia Cuantica en Fisica Molecular
Carlos Garcia Canal (Universidad Nacional de La Plata)
October 4
Abstract: Mostramos que la captura de un electron por una molecula polar, proceso que requiere de un momento dipolar critico, resulta ser la realizacion mas simple de una anomalia cuantica en un sistema fisico real. La interaccion electron-molecula exhibe, en la descripcion clasica, invariancia de escala. Nuestro tratamiento del problema cuantico, en el estilo de la teoria de campos, permite determinar el valor del dipolo critico que surge de la presencia de la anomalia cuantica: violacion de la simetria de escala por efectos de la cuantificacion. Esta notable realizacion de anomalia esta acompañada de una transmutacion dimensional.
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Ultrahigh energy cosmic rays and new physics at the TeV
M. Masip (Universidad de Granada)
September 17
Abstract: Ultrahigh energy neutrinos can be used to explore the physics at the TeV scale. I discuss the neutrino-nucleon cross section in models with extra dimensions and the fundamental scale at the TeV. In particular, I present the contributions mediated by string resonances, the (elastic at the parton level) graviton mediated interactions, and the production of microscopic black holes.
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