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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, Dimecres 14 de Desembre de 2016, a les 12:00h

Seminari de l'Institut de Ciències del Cosmos

Títol: Dark energy from a frozen scalar field
Conferenciant: Fergus Simpson (ICCUB)
Abstract:

Ordinarily, a scalar field may only play the role of dark energy if it possesses a potential that is either extraordinarily flat or extremely fine-tuned. I shall demonstrate that these restrictions need not apply if the scalar field exchanges energy with another fluid. In this scenario, the field may come to rest while displaced from the local minimum of its potential. As a result, any scalar field is capable of forming dark energy, regardless of the shape of its potential. I will present a physically motivated realisation in the form of a derivative neutrino-majoron coupling.

Lloc: Aula Pere Pascual (507). Physics Building, UB
Contacte: secretaria@icc.ub.edu
Web: http://icc.ub.edu/activity/856

Facultat de Física, Dijous 15 de Desembre de 2016, a les 14:00h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: All Vacua Must Die
Conferenciant: Ben Freivogel (University of Amsterdam)
Abstract:

We conjecture that all vacua in string theory decay. More precisely, non-supersymmetric vacua in string theory are at most metastable and eventually decay, while supersymmetric vacua are only marginally stable. All de Sitter vacua with small cosmological constant are metastable to decay via a process that occurs on scales small compared to the horizon size.

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

Facultat de Física, Divendres 16 de Desembre de 2016, 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:

Facultat de Física, Dimarts 20 de Desembre de 2016, a les 14:30h

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: Tensor networks and conformal field theory on the lattice
Conferenciant: Guifré Vidal (Perimeter Institute)
Abstract:

The multi-scale entanglement renormalization ansatz (MERA) has been shown over the last 10 years to offer an accurate description of ground states of quantum critical lattice Hamiltonians in 1+1 spacetime dimensions. It has also been conjectured to be a lattice realization of the AdS/CFT correspondence. In this talk I will describe how MERA defines global and local scale transformations on the lattice, and related notions of invariance / covariance under these transformations. Accordingly, we will see that the ground state of the quantum Ising spin chain is scale invariant (in spite of the presence of an explicit length scale -- the lattice spacing!). We will then also see that, under local scale transformations, the low energy subspace of the lattice model transforms without mixing states in different conformal towers, as expected.

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

Facultat de Física, Dimecres 18 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 V12M (Physics Building, first floor)
Contacte: germani@icc.ub.edu
Web: http://icc.ub.edu/activity/847