Skip navigation.
Home

Events

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

Title: A Heterotic Standard Model with B-L Symmetry and a Stable Proton
Time: 2pm
Place: DRL 2N36

Title: Asymptotic symmetries from soft theorems
Time: 2 pm
Place: DRL 2N36

Title: Soft-pion theorems for large-scale structure
Time: 2pm
Place: DRL 2N36
 
Abstract:
Consistency relations, which relate the squeezed limit of an N+1-point function to an N-point function, are extremely useful nonperturbative statements in cosmology and remain valid when the N-point function is deep in the nonlinear regime.  In this talk I will discuss the derivation of these relations in conformal Newtonian gauge, with velocity potential playing the role of the soft pion; their robustness under astrophysical complications; and the connection to previously derived relations in zeta (unitary) gauge.  As a byproduct of this investigation, I also discuss a simple fluid Lagrangian for large scale structure.

Title: Dark Energy phenomenology: the effective field theory approach
Time 2pm
Place: DRL 2N36
 
Abstract:
I will present recent and ongoing works that aim at a unifying description of dark energy and modified gravity models containing a scalar degree of freedom in addition to general relativity. Such an effective field theory approach allows, on the one hand, a transparent analysis of the possible theoretical mechanisms at the basis of cosmic acceleration; moreover, it provides a useful set of parameters that can be efficiently constrained with observations. I will show the present observational constraints based on the growth rate of cosmic structures and the forecasts for future surveys such as EUCLID.

Title: Building a social network of elliptic fibrations for F-Theory
Time: 2pm
Place DRL 2N36
 
Abstract:
We discuss the gauge groups and matter content for genus one fibrations with their fiber a hypersurface in one of the 16 2D reflexive polytopes, where some of these were already discussed in the literature. The polyhedrons are connected by geometric transitions on the geometry side which translates into a toric Higgs branch on the field theory side. This network structure is symmetric and reflects the mirror symmetry of the polytopes. This allows the identification of discrete symmetries.

Title: Healthy theories beyond Horndeski
Time: 2pm
Place: DRL 2N36

Title: Search for CP Violation in the Gamma Ray Sky
Time: 2pm
Place: 4N9
 
Abstract: Motivated by the possible existence of a cosmological magnetic field with non-trivial
helicity, we evaluate a CP odd statistic, $Q$, using gamma ray data obtained from
Fermi satellite observations at high galactic latitudes. Observed values of $Q$ arefound to be non-zero at the $2\sigma$ level ($3\sigma$ in the northern hemisphere)and also deviate at the same level from values obtained from simulated data. Contaminationfrom the Milky Way does not seem to be responsible for the excess since the signal ispresent even for data at very high galactic latitudes. Assuming that the excess is indeeddue to a helical cosmological magnetic field, our results indicate left-handed magnetic helicityand field strength $\sim 10^{-14}~{\rm G}$ on $\sim 10~{\rm Mpc}$ scales.

Title: Origin of probabilities and their application to the multiverse: Toward a resolution of cosmological measure problems
Time: 11am
Place: DRL 4N12
 
Abstract:
Increasing observational support for cosmic inflation motivates further scrutiny of the challenging open questions related to multiverse theories such as eternal inflation.  Page and others have argued that such theories only make sense if classical probabilities are introduced separately from the quantum ones. I argue using simple models that all successful practical uses of probabilities originate in quantum fluctuations in the microscopic physical world around us, often propagated to macroscopic scales. Thus I claim there is no physically verified fully classical theory of probability. I comment on the general implications of this view, and specifically question the application of classical probability theory to cosmology in cases where key questions are known to have no quantum answer. I argue that the ideas developed here may offer a way out of the notorious measure problems of eternal inflation.

Title: Are Two Metrics Better than One?: The Cosmology of Massive Bigravity
Time: 2 pm
Place: DRL 4N9

Title: Scale Invariance, Radiative Symmetry Breaking and Dark Matter
Time: 2pm
Place: DRL 4N12
 
Abstact:
The discovery of the Higgs and the absence of any New Physics at the LHC
shifts the landscape of BSM model building. Is a natural theory just
pushed to higher scales or were we not careful enough, when interpreting
the argument of Naturalness?
In this talk I want to consider both possibilities. In case of a
high-scale UV completion of the SM, a heavy WIMP could be the first
thing we see. I will discuss new effective theories for such a scenario.

Theories which radiatively induce the Higgs mass parameter by a
Coleman-Weinberg mechanism in a Dark Sector allow to generate all mass
scales in the SM by quantum effects. In the absence of high scale new
physics these models could c

Title: Thermodynamics of gauged dyonic and Proca black holes
Time: 2pm
Place: DRL 4N12

Title: The Null Energy Condition from String Theory
Time: 2 pm
Place: DRL 2N36

Modeling quantum gravity effects in inflation
In this talk I will discuss the quantum structure of slow-roll inflation. Various examples in 3+1 and 1+1 dimensions show that the standard arguments leading to slow-roll eternal inflation (SREI) are not invariant under field redefinitions. A particular case in 1+1d, which by standard arguments should exhibit SREI, is related by a field redefinition to pure Liouville gravity coupled to a free scalar matter field. Aspects of the non-perturbative quantization of Liouville theory will be discussed, and quantum fluctuations of the scale factor will be seen to prevent SREI in this model.

Time: 2 p.m.
Place: 4N12