College of Arts and Sciences

The LHC has accumulated a large luminosity and has already begun ruling out a wide range of theoretical scenarios. I will discuss the theoretical implications of current LHC searches for supersymmetry and the first tentative Higgs measurements. In particular, I will assess the current status of SUSY naturalness, and explain some ways in which searches for the scalar top quark might help to further constrain the parameter space.

Continue reading… Supersymmetry, Naturalness, and the LHC: Where Do We Stand? – Matthew Reece

The effort to detect long-wavelength gravitational waves with a pulsar timing array (PTA) is progressing well, with three major international groups intensifying their efforts and increasingly sharing data and techniques. *Your* PTA, the North American Nanohertz Observatory for Gravitational waves (NANOGrav) is making excellent progress. I will report on our recent results and also comment on my group’s specialty, the effort to remove time variable propagation delays through the ionized interstellar medium.

Continue reading… Gravitational Wave Detection with Pulsars: the NANOGrav collaboration – Dan Stinebring

Results from observational cosmology suggest that our universe is currently accelerating. The simplest explanation is that we are living in a universe with a positive cosmological constant. In this talk, I will describe some recent attempts in constructing such solutions in string theory and discuss the difficulties one encounters in finding metastable de Sitter vacua. Thus, the requirement of positive cosmological constant and stability imposes strong constraints on the string theory landscape.

Continue reading… Hunting for de Sitter vacua in the String Landscape – Gary Shiu

Dark matter candidates in a broad class of non-thermal models produce primordial isocurvature perturbations and non-Gaussianities. We discuss the model dependence of such scenarios. In particular, fermionic superheavy dark matter requires non-gravitational interactions to be observationally interesting. We also present a general mathematical result regarding the cross correlation between the primordial isocurvature perturbations and curvature perturbations. This last result is of general interest for isocurvature phenomenology. Download the slides

Continue reading… Bosonic and Fermionic Non-thermal Dark Matter Isocurvature Perturbations and Non-Gaussianities – Daniel Chung

The idea that the graviton may be massive has seen a resurgence of interest due to recent progress which has overcome its traditional problems. I will review this recent progress, and show how the theory can be extended to write consistent interactions coupling together multiple massive spin-2 fields. Download the slides

Continue reading… Ghost-free multi-metric interactions

I will describe a new model for inflation – Chromo-Natural Inflation – consisting of an axionic scalar field coupled to a set of three non-Abelian gauge fields. The model’s novel requirement is that the gauge fields begin inflation with a rotationally invariant vacuum expectation value (VEV) that is preserved through identification of SU(2) gauge invariance with rotations in three dimensions. The gauge VEV interacts with the background value of the axion, leading to an attractor solution that exhibits slow roll inflation even when the axion decay constant has a natural value (\less M_{\rm Pl}). Assuming a sinusoidal potential for the axion,

Continue reading… Chromo-Natural Inflation – Peter Adshead

Weak gravitational lensing, whereby the images of background galaxies are distorted by foreground matter, can be a powerful cosmological probe if systematics are sufficiently controlled. In particular, I will show how we may use weak lensing to robustly test the standard cosmological constant-dominated “concordance model” of cosmology by using in-hand expansion history data to make predictions for future observations. I will then discuss one recent proposal for economically gathering the necessary data while minimizing systematics — the balloon-borne High Altitude Lensing Observatory (HALO). Download the slides

Continue reading… Testing the concordance cosmology with weak gravitational lensing – Ali Vanderveld

Various data analysis of the Cosmic Microwave Background (CMB) radiation present anomalous features that can be interpreted as indications of statistical isotropy breaking. Some models of inflation involving vector fields predict statistical anisotropy in the correlation functions of primordial curvature perturbations. We employ a simplified vector field model and parametrize the bispectrum of curvature fluctuations in such a way that all the information about statistical anisotropy is encoded in some coefficients lambda_{LM} (representing the ratio of the anisotropic to the isotropic bispectrum amplitudes). We compute an optimal estimator for these coefficients and their Fisher error. We predict a sensitivity for an experiment like Planck to the anisotropic to isotropic amplitudes of about 10% if fNL is around 30.

Continue reading… An estimator for statistical anisotropy from the CMB bispectrum – Ema Dimstrogiovanni

Primordial non-Gaussianity is among the most promising of few observational tests of physics at the inflationary epoch. At present non-Gaussianity is best constrained by the cosmic microwave background, but in the near term large-scale structure data may be competitive so long as the effects of primordial non-Gaussianity can be modeled through the non-linear process of structure formation. I will discuss recent work modeling effects of a few types of primordial non-Gaussianity on the large-scale halo clustering and the halo mass function. More specifically, I will compare analytic and N-body results for two variants of the curvaton model of inflation: (i) a “tau_NL”

Continue reading… Local Primordial non-Gaussianity in Large-scale Structure – Marilena LoVerde

Cosmological inflation is the leading candidate theory for the physics of the early universe, and is in beautiful agreement with current cosmological data such as the WMAP Cosmic Microwave Background measurement. I consider alternatives to inflation with a critical eye, and present a simple argument showing that any model which matches the observed universe must have one of three properties: (1) accelerated expansion, (2) speed of sound faster than the speed of light, or (3) super-Planckian energy density. Download the slides

Continue reading… Inflation, or What? – William Kinney

Hawking’s discovery of black holes radiance along with Bekenstein’s conjecture of the generalized second law of thermodynamics inspired a conceptually pleasing connection between gravity, thermodynamics and quantum theory. However, the discovery that the spectrum of the radiation is in fact thermal, together with the no-hair theorem, has brought along with it some undesirable consequences, most notably the information loss paradox. There have been many proposals to the resolution of this paradox, with the most natural resolution being that during the time of collapse the radiation given off is not completely thermal and can carry small amounts of information with it.

Continue reading… Quantum Kinetics and Thermalization of Hawking Radiation – Dmitry Podolsky

Correlation functions during inflation feature infrared effects that could undermine a perturbative study. I will discuss self-consistent mechanisms of mass generation that regulates infrared physics, and introduce a method based on quantum optics to obtain the decay width of quantum states. Lack of energy conservation entails that EVERY particle acquires a width as a result of emission and absorption of superhorizon quanta thus becoming “quasiparticles”. BLACKBOARD TALK

Continue reading… Condensates and quasiparticles in inflationary cosmology – Daniel Boyanovsky

Cosmological phase transitions occurred. I will talk about recent advances in modeling possible phase transitions when these transitions are mediated by scalar fields. I will discuss first- and second-order transitions, at various scales, and show how we can compute the background of stochastic gravitational waves produced during (and after) these transitions.

Continue reading… Gravitational Waves from Cosmological Phase Transitions – Tom Giblin

General relativity is a generally covariant, locally Lorentz covariant theory of two transverse, traceless graviton degrees of freedom. According to a theorem of Hojman, Kuchar, and Teitelboim, modifications of general relativity must either introduce new degrees of freedom or violate the principle of local Lorentz covariance. In this paper, we explore modifications of general relativity that retain the same graviton degrees of freedom, and therefore explicitly break Lorentz covariance. Motivated by cosmology, the modifications of interest maintain explicit spatial covariance. In spatially covariant theories of the graviton, the physical Hamiltonian density obeys an analogue of the renormalization group equation which encodes invariance under flow through the space of conformally equivalent spatial metrics.

Continue reading… Spatially Covariant Theories of a Transverse, Traceless Graviton – Godfrey Miller