SEMINARIS INTERNS FT/UB (2003-2004)

ABSTRACT: We review the Higgs boson couplings to fermions in Supersymmetric models. We derive the quantum contributions to the effective couplings, and show the existence of large radiative effects. Finally, we show their implication in phenomenological analyses.

ABSTRACT: Within the framework of the current "concordance model", the cosmological constant (CC) has been measured to be positive and could be an explanation for the dark energy component of the universe. However it is difficult to accept, at least from the theoretical point of view, that this parameter is such a small constant. For this reason it has been popular to identify the dark energy with a dynamical scalar field. At present there is no compulsory reason for introducing such an ad hoc field, and moreover one cannot exclude that there is a true cosmological term following a time varying law. Particularly interesting is the possibility that the CC evolves according to a H^2 law. This law can be motivated in various ways within quantum field theory and also on the basis of the so-called holographic principle. In this talk I will discuss some of these issues and I will describe the phenomenological viability of these ideas.

ABSTRACT: Quantum mechanics is a comprehensive deterministic theory truncated to a comprehensible uncertainty-ridden version, in which probabilities reflect the loss of non-local non-accessible information. Being thus a theory of subjective knowledge, jumping is just updating. We review in this seminar the selfcontained way of feeling at ease with quantum mechanics.

ABSTRACT: Despite all the success of the perturbative approach in quantum field theory, there is a host of interesting phenomena for which perturbation theory is inadequate. For them a non-perturbative approach is required, whether because the coupling is strong, or, in case of weak coupling, because there are bound states which are not accessible through perturbation theory.  Dynamical symmetry breaking (DSB) is one of the most important phenomena in physics with an essentially non-perturbative character.  It consists on the rearrangement of the ground state that results from fermion pairing. In this talk I will show you how the theoretical study of the DSB can help us to understand phenomena in areas as different as condensed matter, cosmology and astrophysics. 

ABSTRACT: Recent developments in string theory suggest the existence of a vast landscape of vacua, with more than 10^500 possibilities for the low energy physics. The quantities we usually call "constants of nature" would assume different values in each of these vacua. In this context, anthropic arguments may play a role in comparing theory with observations. After explaining the meaning of anthropic selection, I will discuss the role of inflation in populating the ensemble of vacua. Then, I will review the application of anthropic arguments to the cosmological constant problems, and to the somewhat related issue of neutrino masses.

ABSTRACT: The LHCb experiment will study B Physics in the future Large Hadron Collider at CERN. In this seminar an introduction to the experiment and its L0 trigger will be given and, in more detail, the electrimagnetic L0 trigger will be dealt with. Some studies about its optimisation will be presented as well

ABSTRACT: A microquasar is an X-ray binary star which produces relativistic jets. Galactic microquasars are certainly one of the most recent additions to the field of high energy astrophysics and have attracted increasing interest over the last decade. They are now primary targets for all space-based observatories working in the X-ray and gamma-ray domains. Microquasars provide an excellent laboratory for a suitable study of mass accretion and ejection phenomena in the strong gravitational field of a black hole or neutron star. They also appear as a possible explanation for some of the unidentified sources of high energy gamma-rays (>100 MeV) detected by EGRET. In this talk I will review the main properties of microquasars, giving special attention to the different models for gamma-ray production.

ABSTRACT: Durante la charla describire de forma muy elemental el concepto basico de inflacion y sus predicciones sobre el espectro primordial de perturbaciones. Inflacion podria ser responsable tanto de las anisotropias de temperatura del fondo de radiacion como de la distribucion a gran escala de galaxias y cumulos de galaxias. Los datos recientes de observaciones cosmologicas confirman espectacularmente las predicciones de inflacion y permiten poner restricciones a sus posibles realizaciones.

ABSTRACT: I will describe the detection principles and scientific objectives of the first space borne GW detector: LISA. The talk will also include reference to the precursor mission LPF (LISA Pathfinder), as well as to the role of a Spanish group, based in Barcelona (UB+IEEC+UPC), who is very actively involved in this Project.

ABSTRACT: In this talk, Information Theoty is presented as a theory of inter-conversion between different resources. A unifyed picture of distributed computation, cryptography, communication through channels, etc. is given. It is also explained the analogy between quantum and secret correlations.

ABSTRACT: Around 80% of the universe is made not of matter or radiation but of a mysterious force called dark energy, a kind of gravity in reverse. Dark energy was listed as the breakthrough of the year 2003 in the journal Science (second place went to identification of genes for mental illness, third for evidence of global climate change). In February 2003, the Wilkinson Microwave Anisotropy Probe (WMAP) satellite took the most detailed picture yet of the cosmic microwave background - an image of the infant cosmos when it was less than 400,000 years old. In July 2003, astronomers from the Sloan Digital Sky Survey (SDSS), which aims to map out a million galaxies, published a research paper in which they cross-correlate the (local) galaxy distribution on WMAP's microwave data. They found a significant correlation which they claim provides a new evidence to the existance of dark energy. (Recommended reading: http://segre.ieec.fcr.es/gazta/isw.html and the astro-ph numbers or refs mentioned within this document.)

ABSTRACT: We analize the physical (reduced) space of non-local theories, around the fixed points of these systems, by analyzing: i) the Hamiltonian constraints appearing in the 1+1 formulation of those theories, ii) the symplectic two form in the surface on constraints. P-adic string theory for spatially homogeneous configurations has two fixed points. The physical phase space around q=0 is trivial, instead, around q=1/g is infinite dimensional. For the special case of the rolling tachyon solutions it is an infinite dimensional lagrangian submanifold. In the case of string field theory, at lowest truncation level, the physical phase space of spatially homogeneous configurations is two dimensional around q=0, which is the relevant case for the rolling tachyon solutions, and infinite dimensional around q=M2/g.

ABSTRACT: Back-in-time travel requires the existence of Closed Timelike Curves (CTC) in the spacetime. CTC are not possible in ordinary flat spacetime, or in most physical solutions of Einstein equations, although they are possible in some more exotic solutions. But, if our space had a non trivial topology allowing the existence of the so called wormholes (space shortcuts), it would then be possible to imagine the construction of time machines which would make some CTC possible. I will discuss this as well as other time machines, some related paradoxes, and what kind of restriction the laws of physics impose to macroscopic time travel.

ABSTRACT: The spectral function \rho_{V-A}(s) is determined from ALEPH data on hadronic tau decays using a neural network parametrization
trained to retain the full experimental information on errors, their correlations and the chiral sum rules. Nonperturbative QCD vacuum condensates can then be determined from finite energy sum rules.

ABSTRACT: We present a numerical study of classical particles diffusing on a solid surface. The particles' motion is modeled by an underdamped Langevin equation with ordinary thermal noise. The particle-surface interaction is described by a periodic or a random two dimensional potential. The model leads to a rich variety of different transport regimes, some of which correspond to anomalous diffusion such as has recently been observed in experiments and Monte Carlo simulations. We show that this anomalous behavior is controlled by the friction coefficient, and stress that it emerges naturally in a system described by ordinary canonical Maxwell-Boltzmann statistics.

ABSTRACT: In this talk I will report on baryon resonances that are generated dynamically using a chiral unitary approach for meson-baryon interactions. I will show that two octets and a singlet of J^P=1/2^- states are obtained. In the particular case of the strangeness S=-1 sector, it is found that there are in fact two poles of the scattering meson-baryon T-matrix that represent the nominal Lambda(1405) resonance. Experiments that could potentially filter each one of these resonances are proposed.

ABSTRACT:

One equation for the soft running,
one equation for the ultrasoft running,
and one equation for the potential running,
which rules them all, and at the hard scale binds them.

ABSTRACT: The kaon system offers several opportunities to study direct CP violation in hadronic decays. The most famous one is provided by epsilon' /epsilon, but new observables can be provided also in K->3pi. In this talk I will review the main features and new developments of the interesting observables in K->3pi. I will focus also on the importance of Final State Interactions and on the technics used to calculate them.

ABSTRACT: A number of gravity theories are considered where the lagrangian contains terms growing with the decrease of the scalar curvature. The simplest example is 1/R gravity. Their cosmological properties are investigated. Such models eliminate the need of the dark energy, as the corresponding gravitational terms are responsible for cosmic acceleration. The string/M-theory origin of such effective gravities is shown. The resolution of the appearing instabilities by the introduction of higher derivative terms important for early time inflation is outlined. The appearence of minimal curvature in the universe is also outlined.

ABSTRACT: The existence of two different types of truncations of the field content of a theory is clarified. The conditions to ensure the consistency of a dimensional reduction (Kaluza-Klein) under an algebra of independent Killing vectors are explained. The reduction of the gauge algebra is fully performed and it is shown that some rigid symmetries may remain in the reduced theory. It is also shown that truncations originated by the introduction of constraints will in general be inconsistent but this fact does not prevent the existence of correct upliftings in some cases.

ABSTRACT: Until very recently, the conjectured exact duality between IIB String Theory on AdS(5)xS(5) and N=4 SYM was incredibly hard to check due to, essentially, the lack of proper tools to study both sides beyond supergravity and perturbation theory respectively. Berenstein, Maldacena and Nastase provided a first way out and found a region where string and gauge theory predictions were simultaneously valid, finding a complete agreement. I will discuss (in a hopefully pedagogical way) various recent efforts that have provided some really spectacular checks of the correspondence in sectors of the theories that seemed to be far away from supersymmetry.

ABSTRACT: The purpose of the Coordinated Project is to develop solutions with adequate performance and affordable cost to the data processing problems of the experiments of the Large Hadron Collider (LHC) at CERN. A production rate of 100 events per second, each of about 1 Mbyte in size, is foreseen for each of the LHC experiments. A chain of programs that require substantial CPU capacity accomplishes the analysis of these events. In addition, it is fundamental to generate appropriate amounts of simulated events (Monte Carlo events) in order to compare the data with various Particle Physics models. Given that the collision are independent of each other, solutions based on highly replicated systems of commodity components will be investigated, such as "farms" of PCs with Linux interconnected by Gigabit Ethernet, which when arranged in different configurations can be applied to simulation as well as data analysis. Such systems require development of automation techniques for system and resource management. The key to the project is the interconnection of these "farms" to form an integrated distributed system, both at national and international levels, called a Grid. Subjects of study will include the communication between the national farms, automation of system and data management, and the characteristics of a specialized center that would serve as a gateway for interconnection and data interchange with Grids in other countries. Realistic tests of the system will be done by generating simulated data for the LHC experiments and subsequently analyzing it within the framework of the international LHC Computing Grid.

 

ABSTRACT: In this talk I will present the semiclassical corrections to the Cardy-Verlinde formula of two-dimensional Achucarro-Ortiz (AO) black hole. This computation is performed in the context of KKW analysis. First I briefly review the KKW methodology and give some paradigms for deriving corrections to the temperature and entropy of d(>2)-dimensional black hole spacetime. Then, I show that the entropy of the event horizon of AO black hole spacetime can be described by the Cardy-Verlinde formula. Finally, I derive the self-gravitational corrections to the Cardy-Verlinde formula of AO black hole.

 

ABSTRACT: An interesting example of the deep interrelation between Physics and Mathematics is obtained when trying to impose mathematical boundary conditions on physical quantum fields. This procedure has recently been re-examined with care. We will comment on that and previous analyses, and will make some considerations on the results of the purely mathematical zeta-function method, in an attempt at clarifying the issue. Hadamard regularization can be invoked in order to fill the gap between the infinities appearing in the QFT renormalized results and the finite values obtained in the literature with other procedures.

 

ABSTRACT: In this talk I shall first review the most salient features of the extended chiral quark model, with special emphasis in the matching to QCD short distance properties and chiral symmetry restoration at large Q2. I shall then proceed to analyze in detail two more specialized topics:
1) vector meson properties and effective lagrangians as derived from the extended chiral quark model
2) quark-hadron duality for mesons in the large N_c limit and implications for the Regge trajectories of the theory and the QCD effective string

 

ABSTRACT: Heavy quark-antiquark bound states (bottomonium and charmonium) have long been identified as non-relativistic systems. As such, their dynamics depends at least on three well separated scales: the mass of the heavy quarks (m), the typical three-momentum in the CM frame (mv), and the typical binding energies (mv2), m >> mv >> mv2. In addition, it also depends on the scale controlling non-perturbative effects in QCD (Lambda_QCD). Disentangling the role of each of these scales is crucial in order to understand heavy quarkonium from QCD. The use of Effective Field Theories allows to do this job efficiently. Non-Relativistic QCD (NRQCD) arises after integrating out from QCD degrees of freedom with (non-relativistic) energy and three-momentum of the order of m or larger. I will argue that in order to describe the physics of heavy quarkonium it is convenient to integrate out from NRQCD degrees of freedom of energy mv as well. This produces a further effective theory called Potential NRQCD (pNRQCD). The aspect (degrees of freedom) of this theory depends on the interplay between the scales mv, mv2 and Lambda_QCD. I will focus on the case Lambda_QCD >> mv2, where pNRQCD reduces to a quark-antiquark pair interacting through a (non-perturbative) potential (which also couples to Goldstone bosons), and, hence, it shares many features with phenomenological non-relativistic potential models. In this situation, NRQCD decay matrix elements can be written in terms of wave functions (and derivatives of them) at the origin plus a few bound-state (and heavy flavor) independent non-perturbative parameters. This allows to put forward a number of model independent results for the inclusive decay widths of various heavy quarkonium states.

 

ABSTRACT: It is well known that the renormalization group equations depend on the scale where they are applied. This phenomenon is especially relevant for the massive fields in curved space, because the decoupling effects may be responsible for important cosmological applications like the graceful exit from the inflation and low-energy quantum dynamics of the cosmological constant. We investigate, using both covariant and non-covariant methods of calculation and mass-dependent renormalization scheme, the vacuum quantum effects of massive fields in curved space-time. In the higher derivative sector we arrive at the explicit form of decoupling and obtain the beta-functions in both UV and IR regimes as the limits of general expressions. A particularly interesting case is the renormalization group flow in the theory with broken supersymmetry, where the sign of one of the beta-functions changes on the way from the UV to IR. This property enables one to construct a modified Starobinsky model of inflation which does not require inflaton and does not need the special choice of initial data.

 

ABSTRACT: The interaction of a particle with gravitational perturbations in a non-trivial background may lead to Lorentz-breaking modifications of the dispersion relation of the particle, even if the Lorentz group is a fundamental symmetry of the underlying fundamental theory. We study those modifications for the case of a scalar particle propagating in a thermal bath of gravitons in Minkowski spacetime. For this purpose we compute the self-energy of the scalar field within the real-time approach to thermal field theory. The real part of the retarded self-energy gives the correction to the mass and the dispersion relation of the particle, while the imaginary part (which vanishes to lowest order) gives the rate of approach to the equilibrium.