Laboratoire de Physique
Theorique d'Orsay

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Bâtiment 210
Univ. Paris-Sud 11
91405 Orsay Cedex
France
T. 01 69 15 63 53
F. 01 69 15 82 87



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Cosmology and gravity seminars 2017-2018

Les séminaires se tiennent en salle 110 au 1er étage du bâtiment 210, jeudi à 14h.

Seminars are held in room 110, 1st floor of building 210, thursdays at 2.00 p.m.

Contact :Eugeny.Babichev


Upcoming seminars

-  Thursday November 23, 2pm, room 110

Gabriel Jung (LPT) : Non-Gaussianity in two-field inflation beyond the slow-roll approximation

In this talk, I will discuss the level of bispectral non-Gaussianity produced in two-field inflation models with standard kinetic terms. Even though the Planck satellite has so far not detected any primordial non-Gaussianity, it has tightened the constraints significantly, and it is important to better understand what regions of inflation model space have been ruled out, as well as prepare for the next generation of experiments that might reach the important milestone of Delta f_NL(local) = 1. I will present our results on the non-Gaussianity parameter f_NL in the case of sum potentials and show that it is very difficult to satisfy simultaneously the conditions for a large f_NL and the observational constraints on the spectral index n_s in the slow-roll approximation. I will then discuss the case of monomial potentials and show explicitly the small region of parameter space in which this is possible. Finally, I will extend these results beyond the slow-roll approximation and illustrate them with two explicit inflation models.


Past seminars

-  Thursday October 19, 3pm, room 110

Shinji Mukohyama (Yukawa Institute, Kyoto) : Towards a new scenario of inflationary magnetogenesis

In the context of a U(1) gauge theory nonminimally coupled to scalar-tensor gravity, we find a cosmological attractor solution that represents a de Sitter universe with a homogeneous magnetic field. The solution fully takes into account backreaction of the magnetic field to the geometry and the scalar field. Such a solution is made possible by scaling-type global symmetry and fine-tuning of two parameters of the theory. If the fine-tuning is relaxed then the solution is deformed to an axisymmetric Bianchi type-I universe with constant curvature invariants, a homogeneous magnetic field and a homogeneous electric field. Implications to inflationary magnetogenesis are briefly discussed.

-  Thursday October 12, 2pm, room 110

Lukas Witkowski (APC Paris) : Super-Planckian scalars ?

Scalar fields with super-Planckian field ranges play an important role in models of large-field inflation and are also employed in cosmological solutions to the electroweak hierarchy problem. One difficulty in constructing such models is that for super-Planckian field values quantum-gravitational effects cannot be ignored. In particular, ultraviolet physics is expected to constrain the field range over which scalars can exhibit a monotonic potential, which in turn has consequences for models of inflation. To study theories of super-Planckian scalars some knowledge of ultraviolet physics is thus necessary. String Theory is a candidate theory of Quantum Gravity and a suitable framework for addressing this question. Another approach is based on the Weak Gravity Conjecture - an as yet unproven theorem regarding consistent theories of Quantum Gravity. In this talk I want to report on recent progress in the study of super-Planckian scalars. In particular, I will explain how the existence of super-Planckian scalars is increasingly called into question by both String Theory and the Weak Gravity Conjecture.

-  Thursday September 28, 2pm, room 110

Sergey Sibiryakov (CERN) : Beta-functions and asymptotic freedom in (2+1)-dimensional Horava gravity