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.
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 finetuned. 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 neutrinomajoron coupling.

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

Seminari del Dep. de Física Quàntica i Astrofísica

Títol: 
The role of soft modes in deSitter 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 deSitter. 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 deSitter), 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: 

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 multiscale 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: 

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 lowenergy 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 
