# Nonperturbative quantum field theory in curved spaces: the effective potential in de Sitter

Orateur:
Diana Lopez Nacir
Lieu:
483A Malevitch
Horaire:
Tuesday, 29. October 2013 - 14:00

Quantum field theory on curved space-times is a very powerful framework for the study of quantum phenomena in situations where the gravitation itself can be treated classically. Of special interest is the study of interacting quantum fields in de Sitter space-time, where previous studies have reveled that the standard perturbative expansion gives rise to corrections that secularly grow with time and/or infrared divergences. This has motivated the consideration of alternative techniques and in particular the use of resummation schemes.

# A new mechanism for curvature perturbations

Orateur:
Lingfei Wang
Lieu:
483A Malevitch
Horaire:
Tuesday, 22. October 2013 - 14:00

I will explain the spectator scenario and show its advantages compared to the curvaton scenario, under the latest Planck constraints. The spectator scenario generates a smaller non-Gaussianity, negligible isocurvature perturbations, and less tuning. It agrees well with the current Planck data in the visible sector inflation setup, as an example. It also explains the CMB dipole asymmetry with a brief fast roll phase. I will close the talk by proposing the CMB power multipoles, as an alternative approach independent of the CMB dipole asymmetry model.

# Searching for sterile neutrinos in lab and in space

Orateur:
Oleg Ruchayskiy
Home Institute:
EPFL, Lausanne
Lieu:
454A-Luc Valentin
Horaire:
Friday, 11. October 2013 - 14:00

If LHC discovers only the Higgs boson and finds no signatures of new physics (thus confirming the Standard Model) the necessity to explain the observed beyond-the-Standard-Model (BSM) phenomena, in particular neutrino masses, Dark Matter and matter-antimatter asymmetry of the Universe, should largely shape the further development of particle physics. I will describe a unique testable approach that provides the resolution of all these BSM problems.

# Higher-order singletons and partially massless fields

Orateur:
Xavier Bekaert
Home Institute:
Tours
Lieu:
483A Malevitch
Horaire:
Tuesday, 8. October 2013 - 14:00
Using ambient space we develop a fully gauge and o(d,2) covariant approach to boundary values of AdS(d+1) gauge fields. It is applied to the study of (partially) massless fields in the bulk and (higher-order) conformal scalars, i.e. singletons. We prove the appropriate generalization of the Flato-Fronsdal theorem on the decomposition of the tensor product of two singletons, which is in agreement with the known structure of symmetries for the higher-order wave operator.

# Brane SUSY Breaking and inflation: implications for scalar fields and CMB distorsion

Orateur:
Augusto Sagnotti
Home Institute:
Scuola Normale, Pisa, Italie
Lieu:
483A Malevitch
Horaire:
Tuesday, 24. September 2013 - 14:00
I elaborate on a link between the string–scale breaking of supersymmetry that occurs in a class of superstring models and the onset of inflation. The link rests on spatially flat cosmologies supported by a scalar field driven by an exponential potential. If, as in String Theory, this potential is steep enough, under some assumptions that are spelled out in the text the scalar can only climb up as it emerges from an initial singularity.

# Type-I cosmic string network

Orateur:
Daisuke Yamauchi
Lieu:
454A-Luc Valentin
Horaire:
Wednesday, 18. September 2013 - 14:00

We study the network of Type-I cosmic strings using the field-theoretic numerical simulations in the Abelian-Higgs model. For Type-I strings, the gauge field becomes responsible for the bulk motion of strings, and thus we find that the correlation length of the strings is strongly dependent upon the parameter $\beta$, the ratio between the self-coupling constant of the scalar field and the gauge coupling constant. In particular, if we take the cosmic expansion into account, the network becomes densest in the comoving box for a specific value of $\beta$ for $\beta<1$.

# Unconventional Supersymmetry

Orateur:
Jorge Zanelli
Home Institute:
Institut de Physique theorique de Valdivia, Chili
Lieu:
483A Malevitch
Horaire:
Tuesday, 17. September 2013 - 14:00

A gauge theory for a superalgebra that could describe the low energy particle phenomenology is presented. The system includes an internal gauge connection one-form A, a spin-1/2 Dirac fermion ψ in the fundamental representation of the internal symmetry group, and a Lorentz connection ωab.

In contrast with standard supersymmetry, here bosons are all s=1 gauge potentials; fermions are Dirac particles covariantly coupled to the gauge potentials. Additionally, in this theory

- The number of fermionic and bosonic states is not necessarily the same;

# Large Tensor-to-Scalar Ratio in Small-Field Inflation

Orateur:
Takeshi Kobayashi
Home Institute:
CITA
Lieu:
454 Valentin
Horaire:
Tuesday, 30. July 2013 - 14:00

We show that density perturbations seeded by the inflaton can be suppressed when having additional light degrees of freedom contributing to the production of perturbations. The inflaton fluctuations affect the light field dynamics by modulating the length of the inflationary period, hence produce additional density perturbations in the post-inflationary era. Such perturbations can cancel those generated during inflation as both originate from the same inflaton fluctuations.

# Reconstructing the primordial power spectrum

Orateur:
Dhiraj Kumar Hazra
Home Institute:
APCTP, Korea
Lieu:
483A Malevitch
Horaire:
Thursday, 18. July 2013 - 14:00

Power spectrum from the primordial perturbations can be reconstructed directly from the Cosmic Microwave Background (CMB) observations in a model independent way. In this context, error sensitive Richardson-Lucy (RL) deconvolution algorithm has been used previously to reconstruct the power spectrum from CMB data. In this talk I shall initially discuss earlier literatures towards this reconstruction. After providing a broad overview of the method I shall discuss the scopes of improvizing the algorithm to make it faster and efficient and to broaden its applications.

# Galaxy-dark matter connection: the large scale structure view

Orateur:
Uros Seljak
Home Institute:
Berkeley
Lieu:
483A Malevitch
Horaire:
Monday, 15. July 2013 - 14:00

Large scale distribution of galaxies is believed to be determined by the dark matter distribution, but their
detailed relationship remains unknown. Weak lensing and galaxy clustering can be used to study their