Time: 2pm

Place: 2N36

# Events

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 4N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Time: 2pm

Place: 2N36

Title: Cosmological billiards and hyperbolic Weyl groups

Time: 2pm

Place: 2N36

Abstract: The BKL analysis of spacelike singularities in cosmology gives evidence for a chaotic behavior of the four-dimensional spacetime metric near the singularity. This can be understood as a billiard motion in the Weyl chamber of a hyperbolic Kac-Moody algebra, which is an infinite-dimensional extension of the Lie algebra sl(2,R). Thus the billiard motion is controlled by the Weyl group of the hyperbolic algebra, which can be realized as the modular group PGL(2,Z). The billiard description can be applied also to 11-dimensional supergravity, the low energy limit of M-theory. In this case sl(2,R) is replaced by the exceptional Lie algebra E8, with the hyperbolic extension E10. I will in my talk explain how the modular realization of the Weyl group can be extended to the E10 case by generalizing the rational integers Z to an integer version of the eight-dimensional algebra of octonions.

Title: Cosmology in Massive GravityLand

Time: 2pm

Place: 2N36

Abstract: The last years have seen a renewed interest in theories of massive gravity. They represent an infra-red modification of gravity where the gravitational force weakens at very large scales. Heuristically, they provide the playground to understand a possible modification of GR which could potentially provide a dynamical solution to the cosmological constant problem. In this talk I will discuss a number of theoretical aspects of massive gravity theories, focusing on the relevance of the so-called Vainstein mechanism, both at the classical and the quantum level. I will also discuss how we can use cosmology from the early and late universe to constrain these theories. For example, what does the Cosmic Microwave Background Radiation know about the graviton mass?

Title: From the High Scale to the LHC in the Minimal SUSY B-L Model

Time: 2pm

Place: 2N36

Title: Flux Compactifications Grow Lumps

Time: 2pm

Place: DRL 4N9

Title: The Universe as a Cosmic String

Time: 2 pm

Place: DRL 2N36

Abstract: We are investigating modifications of general relativity that are operative at the largest observable scales. In this context, we are investigating the model of brane induced gravity in 6D, a higher dimensional generalization of the DGP model. As opposed to different claims in the literature, we have proven the quantum stability of the theory in a weakly coupling regime on a Minkowski background. In particular, we have shown that the Hamiltonian of the linear theory is bounded from below. This result opened a new window of opportunity for consistent modified Friedmann cosmologies. In our recent work it is shown that a brane with FRW symmetries necessarily acts as a source of cylindrically symmetric gravitational waves, so called Einstein-Rosen waves. Their existence essentially distinguishes this model from its codimension-one counterpart and necessitates to solve the non-linear system of bulk and brane-matching equations. A numerical analysis is performed and two qualitatively different and dynamically separated classes of cosmologies are derived: degravitating solutions for which the Hubble parameter settles to zero despite the presence of a non-vanishing energy density on the brane and super-accelerating solutions for which Hubble grows unbounded. The parameter space of both the stable and unstable regime is derived and observational consequences are discussed: It is argued that the degravitating regime does not allow for a phenomenologically viable cosmology. On the other hand, the super-accelerating solutions are potentially viable, however, their unstable behavior questions their physical relevance.

Title: Particle Production from Cosmic Strings

Time: 1pm

Place: 4N9

Abstract: Cosmic strings form when an Abelian symmetry is spontaneously broken. How can we determine if the universe is permeated by a network of cosmic strings, and what would it teach us about physics beyond the Standard Model? If the symmetry breaking scale is high (say GUT scale), then the strings are so massive that they should have been detected through lensing of the cosmic microwave background. Lighter strings cannot be exposed by gravitational probes, and we must look for evidence of them through their particle emission. For instance, radiation from the string may induce an electromagnetic cascade that is detected on Earth in the form of a diffuse gamma ray flux. I will discuss cosmic strings in a generic “hidden sector” extension of the Standard Model, which has often been studied in the context of dark matter, collider phenomenology, and electroweak baryogenesis. The Standard Model fields couple to the cosmic string, and I’ll show how this leads to particle production, and I’ll also discuss the associated cosmological and astrophysical signatures.

Title: Unwinding the Landscape

Time: 2pm

Place: DRL 2N36

Title: New ideas for dark energy and for B-mode dust diagnostics

Time: 2 pm

Place: DRL 2N36

Title: An Effective Theory for Holographic RG Flows

Time: 2pm

Place: DRL 2N36

Abstract:

QFTs can be viewd as RG flows between CFT fixed points. For those CFTs with a holographic dual, it is useful to introduce a bulk action that describes a generic RG flow. I will argue that the bulk action is the effective action for the goldstone boson of the broken (AdS) radial symmetry, providing an AdS analog of the EFT of Inflation. In even dimensions, we use the effective bulk theory to compute the on-shell boundary induced action, which agrees with the dilaton action associated with the RG flow, with correct UV and IR conformal anomalies. In two dimension, this computation can be done without further assumptions. In higher dimensions we take a `slow-flow' limit analogous to the assumption of slow-roll in Inflation, focusing on terms proportional to the difference of the A-type anomalies.

Title: Conformal Fermi coordinates and the local universe formalism

Time: 2pm

Place: DRL 2N36