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El límit per poder anunciar en paper seminaris i conferències en els ascensors és el divendres a les 12 hores de la setmana anterior. Amb posterioritat a aquesta data el seminari o conferència quedarà només recollit al web de la Facultat. Aleshores la publicitació en paper serà responsabilitat dels organitzadors.



Facultat de Física, de Dimecres 18 de Gener de 2017 a Divendres 20 de Gener de 2017, a les 09:00h

Workshop de l'Institut de Ciències del Cosmos

Títol: The vacuum of the Universe: from cosmology to particle physics
Conferenciant:
Abstract:

Our Universe is undergoing an accelerated expansion driven by an unknown form of gravitational vacuum energy; in addition, a mysterious form of (dark) matter is pervading our Universe.

In the first “vacuum” workshop, we have gone deep into all theoretical possibilities that have the potentials to explain the current expansion of our Universe. However, as we have seen, most of these require fine tunings on some parameters and/or initial conditions. The natural question we want to explore is then whether anthropic considerations might (or might not) give any scientifically sound support to these tunings.

The second question we want to explore is what could dark matter be. So far, most of the experimental and theoretical efforts have been focused on low-energy supersymmetry. However, this possibility is by now severely constrained. Thus, in this second “vacuum” workshop, we will focus on the two other most natural candidates of dark matter: primordial black holes and (stringy and non) axions.

The aim of these series of workshops is to bring together scientists from different scientific backgrounds to discuss and exchange ideas about fundamental questions related to what the Universe\\\'s vacuum is, what are its gravitational and particle physics properties and how do they interlock, if they do.

Lloc: Room 202 (Chemistry Building, second floor)
Contacte: germani@icc.ub.edu
Web: http://icc.ub.edu/activity/847

Facultat de Física, Divendres 20 de Gener de 2017, a les 12:00h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: Andy Lütken (University of Oslo)
Conferenciant: Elliptic mirror of the quantum Hall effect
Abstract:

A toroidal sigma-model of magneto-transport is analysed, in which integer and fractional quantum Hall effects are automatically unified by a holomorphic modular symmetry, whose group structure is determined by the spin-structure of the target space. Hall-quantisation is protected by the topology of stable holomorphic vector bundles on tori, and plateaux values of the Hall-conductivity are rational because such bundles are classified by a rational number called the slope.

By exploiting a quantum equivalence called mirror symmetry, this model is mapped to a tractable mirror model, in which topological protection is offered by more familiar winding numbers. The phase diagram and partition function of the mirror model is compared to some of the experimental and numerical data accumulated over the past three decades. The geometry of scaling flows extracted from quantum Hall experiments is in good agreement with modular predictions, including the location of many quantum critical points.

One toroidal model gives a value of the critical delocalisation exponent that agrees with the best available numerical value at the per mille level, suggesting that the toroidal model is in the same universality class as the Chalker-Coddington model. The real delocalisation exponent can be disentangled from other scaling exponents in finite-size scaling experiments, giving an experimental value that is smaller than the toroidal value. We explain why this is another success of the modular model.

Lloc: Aula 507
Contacte: hofer@fqa.ub.edu
Web:

Facultat de Física, Divendres 20 de Gener de 2017, a les 10:30h

Confèrencia del Dep. de Física de la Matèria Condensada

Títol: Morphology and dynamics of bubbles rising in complex fluids
Conferenciant: Raphael Poryles (Laboratoire de Physique, ENS-Lyon)
Abstract:

We study experimentally bubbles rising in different complex fluids confined in a vertical Hele-Shaw cell. The first experiment focuses on the morphology and dynamics of a single bubble rising in a polymer solution (Polyethylene Oxyde, PEO). This fluid is characterized as shear-thinning and viscoelastic. Different regimes are reported depending on the bubble volume. It can present a singularity (“cusp”) at its rear, and/or exhibit spontaneous instabilities. These instabilities can be either a deflection of the bubble trajectory or its fragmentation. The second experiment consists of gas injection at constant flow rate at the base of an immersed granular layer. It generates a fluidized zone consisting of a central air channel and two granular convection rolls on its sides. We investigate the size of the fluidized zone as well as the bubbles trapped in the granular bed.

Lloc: Aula-seminari Eduard Fontseré (aulari)
Contacte: jordi.ortin@ub.edu
Web:

Facultat de Física, Dijous 26 de Gener de 2017, a les 14:00h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: Probing ultralight bosons with black holes and gravitational waves
Conferenciant: Paolo Pani (Università di Roma La Sapienza)
Abstract:

Ultralight bosonic fields (e.g. stringy axions, axion-like particles, dark photons, light spin-2 fields) are compelling dark-matter candidates and provide a serious alternative to the WIMP paradigm. These fields have eluded particle detectors so far, but can dramatically affect the strong-gravity dynamics of compact objects in various detectable ways. Light bosonic fields can trigger black-hole superradiant instabilities which have peculiar signatures, e.g. they produce ``gaps'' in the black-hole Regge plane. This effect can be used to constrain axion-like particles, to derive bounds on light vector fields and on the mass of the graviton, as well as to constrain the fraction of primordial black holes in dark matter. Because of their tiny mass and coupling to the Standard Model, detecting axions and other light bosons in the lab is extremely challenging. However, boson condensates formed through superradiance would emit a periodic gravitational-wave signal whose frequency (related to the boson mass) can be in the optimal range for present and future gravitational-wave interferometers. The theoretical potential of these phenomena as almost-model-independent smoking guns for physics beyond the Standard Model are presented.

Lloc: Aula 507
Contacte: hofer@fqa.ub.edu
Web:

Facultat de Física, Divendres 10 de Febrer de 2017, a les 12:00h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: CP violating scalar Dark Matter
Conferenciant: Venus Keus (University of Helsink)
Abstract:

I will talk about an extension of the Standard Model (SM) in which two copies of the SM scalar SU(2) doublet which do not acquire a Vacuum Expectation Value (VEV), and hence are inert, are added to the scalar sector. We allow for CP-violation in the inert sector, where the lightest inert state is protected from decaying to SM particles through the conservation of a Z_2 symmetry. The lightest neutral particle from the inert sector, which has a mixed CP-charge due to CP-violation, is hence a Dark Matter (DM) candidate. I will discuss the new regions of DM relic density opened up by CP-violation, and compare our results to the CP-conserving limit and the Inert Doublet Model (IDM). We constrain the parameter space of the CP-violating model using recent results from the Large Hadron Collider (LHC) and DM direct and indirect detection experiments.

Lloc: Aula 507
Contacte: hofer@fqa.ub.edu
Web:

Facultat de Física, Divendres 17 de Febrer de 2017, a les 12:00h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: The role of soft modes in de-Sitter and inflation
Conferenciant: Ricardo Ferreira
Abstract:

During the accelerated expansion of the universe scalar and tensor modes are stretched outside the Hubble horizon. Although these modes are locally indistinguishable from a coordinate transformation they break the symmetries of de-Sitter. In this talk I will present the asymptotic charges associated with these soft modes and show how do they affect local vacua. In particular I will show that the different vacua in the inflated patch become orthogonal to each other when t_dS -> M_p^2/H^3 (the equivalent of the Page time for de-Sitter), signaling the breakdown of the perturbative description, as previously suggested in the literature.

Finally, I will comment on more recent work where the connection between the charge, Bogolyubov transformations and coordinate transformations is made. That allows to go beyond perturbation theory and derive probability distributions for the power spectrum of scalar perturbations.

Lloc: Aula 507
Contacte: hofer@fqa.ub.edu
Web: