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Title: "Constraining the CKM matrix with B -> K\pi\pi decays"
Speaker: Dan Pirjol (Bucharest, IFIN-HH)
Date: Divendres 27-juny-2008; 12:00h
Place: Aula 505
The talk presents a new class of constraints on the CKM matrix from
Dalitz analyses of B(s) -> K\pi\pi decays. After a review of the existing direct determinations of the weak phases in the Standard Model, a new constraint is derived, which is based on an analysis of electroweak penguin contributions to B -> K*\pi decays. This gives a linear constraint in the
(\rho,\eta) plane, with small hadronic uncertainties. Using recent data from BABAR a numerical analysis of this constraint is presented, along with a discussion of its sensitivity to new physics.
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Title: "Parity doubling from Weinberg sum rules"
Speaker: Domènec Espriu (UB)
Date: Divendres 6-juny-2008; 12:00h
Place: Aula 505
We investigate the relation among slopes and intercepts of Regge
trajectories for mesons of a given spin and different parities using large
N_c arguments and the matching to perturbative QCD in the deep-Minkowski
region. For spin-1 mesons of opposite parities we prove that: a) for large
and increasing N_c, the scale \Lambda^{(V,A)} separating the
resonance-dominated and the perturbative-saturated region in the channels
V,A grows as \sqrt{N_c}; b) to satisfy the Weinberg sum rules the slopes
of Regge trajectories for mesons of opposite parities must coincide; c)
their intercepts may differ and their difference corresponds to the
difference between \Lambda^V and \Lambda^A. Some arguments indicate that
this difference should tend to zero as N_c\to\infty.
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Title: "IR loop correction during inflation"
Speaker: Takahiro Tanaka (Kyoto University)
Date: Divendres 9-maig-2008; 12:00h
Place: Aula Pere Pascual (507)
If we naively compute the amplitude of fluctuation during inflation, we will easily find IR divergence even at the level of one-loop correction.
We discuss the origin of this divergence and what are the necessary ingredients to define finite observable quantities for the observer like us. There are two key points: one is the local nature of the observable quantity and the other is to pick up one decohered history from the quantum state of the whole universe. The latter issue is hard to tackle in general, but we propose one practical method of taking into account the effect of decoherence to define finite observables.
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Title: "Black holes as elementary particles in superspace and quantum unitarity"
Speaker: Hoi-Lai Yu (Academia Sinica, Taiwan)
Date: Divendres 25-abril-2008; 12:00h
Place: Aula Pere Pascual (507)
The arena for quantum gravity is not spacetime but Superspace. Here we adopt a conservative approach based upon continuum physics and exact canonical quantization. The associated Wheeler-DeWitt equation with evolution in the intrinsic superspace time is a free massive Klein-Gordon equation; and the Hamilton-Jacobi semi-classical limit of plane wave solutions can be matched to the interiors of Schwarzschild black holes. Classical black hole horizons and singularities correspond to the boundaries of the Rindler wedge. Exact wavefunctions of the Dirac equation in superspace are also considered. Precise correspondence between Schwarzschild black holes and free particle mechanics in superspace is noted. Despite the presence of classical singularities, hermiticity of the Dirac Hamiltonian operator, and thus unitarity of the quantum theory, is equivalent to an appropriate boundary condition which must be satisfied by the quantum states. This boundary condition holds for quite generic quantum wavepackets of energy eigenstates, but fails for the usual Rindler fermion modes which are eigenstates with zero uncertainty in energy. From this perspective, the quantum evolution for spherically symmetric gravity is thus physically unitary; and the boundary condition guaranteeing unitarity is much milder than, say, ``Quantum Censorship" requirement of vanishing wavefunction at the boundary.
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Title: "Non-local operators in gauge theories"
Speaker: Jaume Gomis (Perimeter Institute, Canada)
Date: Divendres 18-abril-2008; 14:00h
Place: Aula Pere Pascual (507)
We give an overview of non-local operators in gauge theories and
their gravity duals.
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Title: "Neither black holes nor regular solitons: a no-go theorem "
Speaker: Alessio Celi (UB)
Date: Divendres 14-març-2008; 12:00h
Place: Aula Pere Pascual (507)
By studying the BPS equations for electrostatic and spherically symmetric configurations in N=2, d=5 gauged supergravity with vector multiplets and hypermultiplets coupled, we demonstrate that no regular supersymmetric black-hole solutions of this kind exist. Furthermore, we demonstrate that it is not possible to construct supersymmetric regular solitons that have the above symmetries. As a consequence the scalar flow associated to the BPS solutions is always unbounded.
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Title: "Bicycling Black Rings"
Speaker: María José Rodríguez (UB)
Date: Divendres 7-març-2008; 14:00h
Place: Aula Pere Pascual (507)
We present detailed physics analyses of two different 4+1-dimensional asymptotically flat vacuum black hole solutions with spin in two independent
planes: the doubly spinning black ring and the bicycling black ring system ("bi-rings"). The latter is a new solution describing two concentric orthogonal rotating black rings which we construct using the inverse scattering technique.
We will focus particularly on extremal zero-temperature limits of the solutions.
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Title: "Non-renormalization of the entropy of BTZ black holes "
Speaker: Bindusar Sahoo (Harish-Chandra Institute, India)
Date: Divendres 15-febrer-2008; 12:00h
Place: Aula Pere Pascual (507)
Using AdS/CFT correspondence Krauss and Larsen haveargued that the entropy of a BTZ black hole in a 3-dimensional theory of supergravity with (0,4) supersymmetry doesn't receive any corrections. We look at the possible origin of this amazing result. We find that as a result of AdS/CFT, one can argue that the action of a three dimensional theory of supergravity with (0,4) supersymmetry doesn't receive any correction except for those terms that can be removed by field redefinition. Since Wald's formula is invariant under field redefinition, the non-renormalizability of the entropy follows.
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Title: "Wilson Line Inflation"
Speaker: Anastasios Avgoustidis (UB)
Date: Divendres 25-gener-2008; 12:00h
Place: room 507
I will present a model of inflation in string theory, where the inflaton field corresponds to a Wilson line in the worldvolume of a D-brane, and in the presence of magnetic flux. Inflation ends in a hybrid fashion, when the Wilson line achieves a critical value and an open string mode becomes tachyonic. This scenario predicts a nearly flat, or red tilted, spectrum of scalar perturbations, with negligible primordial gravitational waves. Interestingly, there is a simple compactification in which the eta-problem, appearing in models of brane inflation, is absent.
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Title: "Spontaneous P-parity breaking in dense baryon (quark/nuclear) matter"
Speaker: Alexander Andrianov (UB)
Date: Divendres 14-desembre-2007; 12:00h
Place: room 507
After a qualitative description of what is dense baryon matter a brief retrospective on possibilities of pion condensation will be done starting from ideas of A.Migdal. Then it will be shown how the introduction of a finite baryon density may trigger spontaneous parity violation in QCD. The analysis is done using a low-energy effective realization of QCD at large chemical potentials, that retain the lowest two scalar and pseudoscalar multiplets. We expect that our approach would be relevant for dense nuclear matter in the hadronic phase of QCD in an intermediate regime of 3--12 normal nuclear densities where quark percolation does not yet play a significant role.
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Title: "QED bound states at Finite Temperature using effective" -Assistència permesa només als estudiants de doctorat/màster.
Speaker: Miguel Ángel Escobedo (UB)
Date: Divendres 30-novembre-2007; 12:00h
Place: room 507
In this talk we are going to ilustrate how to apply non-relativistic QED (NRQED) and potencial NRQED (pNRQED) at finite temperature. For this we study hydrogen atom and muonic hydrogen in a wide range of temperature, until the bound states are melted. The motivation of this is the analogy with heavy quarkonium in quark gluon plasma.
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Title: "Eternal inflation and memory of initial conditions"
Speaker: Jaume Garriga (UB)
Date: Divendres 23-novembre-2007; 12:00h
Place: room 507
Generic models of inflation have the property of being eternal to the future. Because of that, one expects that memory of initial conditions is lost in the long run. However, it has recently been realized that bubbles nucleating in an inflating false vacuum retain some information about the initial surface where that false vacuum started, regardless of the length of the intervening inflationary period.
I will discuss this phenomenon, which has been dubbed "the persistence of memory".
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Title: "The clock ambiguity and the emergence of physical laws"
Speaker: Alberto Iglesias (UC Davis)
Date: Divendres 9-novembre-2007; 12:00h
Place: room 507
The process of identifying a time variable in time reparameterization invariant theories results in great ambiguities about the actual laws of physics described by a given theory. A theory set up to describe one set of physical laws can equally well be interpreted as describing any other laws of physics by making a different choice of time variable or ``clock''. I will show how this ``clock ambiguity'' arises and then discuss how one might still hope to extract specific predictions about the laws of physics even when the clock ambiguity is present. As a step in this direction, I will compare the Hamiltonian of a local quantum field theory with a completely random Hamiltonian finding that any random Hamiltonian (constructed in a sufficiently large space) can yield a ``good enough'' approximation to a local field theory. Based on this result I will argue that theories that suffer from the clock ambiguity may in the end provide a viable fundamental framework for physics in which locality can be seen as a strongly favored (or predicted) emergent behavior, and speculate on how other key aspects of known physics such as gauge symmetries and Poincare invariance might be predicted to emerge in this framework.
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Title: "Delta N formalism for cosmological curvature perturbations"
Speaker: Misao Sasaki (Yukawa Institute for Theoretical Physics, Kyoto)
Date: Divendres 19-octubre-2007; 14:00h
Place: room 507
The delta N formalism is a useful method for calculating cosmological curvature perturbations. In particular, it is powerful for evaluating the curvature perturbations from inflation. In this talk, I will review this formalism and discuss its applications to the evaluation of non-Gaussian perturbations from inflation, which has been recently a topic of great interest in cosmology.
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Title: "Footprints of infrared modifications of gravity at short distances" - NOTE: Unusal time (15:00) and Unusal room: Seminari FFN, Aula 320, 3rd Floor.
Speaker: Oriol Pujolas (NYU)
Date: Dijous 6-setembre-2007; 15:00h
Place: room 320 (FFN seminar room, 3rd Floor)
The present accelerated expansion of the universe can be
accounted for either by changing the matter sector
(introducing some form of Dark Energy) or by modifying gravity
at large distances. I will discuss two ways to discriminate
between the two options at short distances. The first relies
on the gravitational effects produced by domain walls. While
in GR domain walls produce a repulsive force, in infrared
modifications of gravity such as the DGP model walls with
small enough tension generate no gravitational field. In
contrast with any other sources, this difference persists at
arbitrarily small distances. I will also argue that the
presence of Lorentz violating phenomena in high energy
processes would indicate that gravity is modified at large
distances. In IR modifications of gravity, the source of
Lorentz violation can be screened and as a consequence may not
affect the background spacetime. This leads to relax the
bounds on Lorentz violating operators, to the point that their
effects could be potentially observable in the near future.
NOTE: Unusal time (15:00)
NOTE: Unusal room: Seminari FFN, Aula 320, 3rd Floor.
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