College of Arts and Sciences

In order to pin down the fundamental nature of dark energy, and thus to understand what most of the Universe is actually made of, new and more precise observations are required, along with more efficient and reliable statistical techniques to interpret those observations correctly and to understand the implications they have for our theoretical models of the Universe. The outstanding challenge posed by the nature and properties of dark energy is giving rise to a flourishing of proposals for new observational campaigns. Type Ia supernovae, gravitational lensing, cluster counts and baryonic acoustic oscillations are some of the techniques available to study dark energy,

Continue reading… Probing dark energy with cosmology – Roberto Trotta

The IceCube neutrino observatory under construction at the South Pole is designed to detect high energy (TeV-PeV) neutrino emission from astrophysical objects, such as the sources of galactic and extragalactic cosmic rays. Data is being taken with the partially- built detector, now half complete with 40 strings and 2400 optical modules, and initial results are now available. In addition to astrophysical studies, IceCube also has a broad particle physics program that will be enhanced by the addition of the IceCube Deep Core, a dense, contained subarray that will push IceCube’s energy reach down to 10-20 GeV and improve its sensitivity to dark matter,

Continue reading… Astrophysics and Particle Physics with IceCube – Tyce DeYoung

I will review some very general properties that must characterize any relativistic UHECR accelerator, and I will list some key observational constraints on the accelerators. In combination these make it unlikely that any of the conventional source candidates can be solely responsible for the observed cosmic rays about about 60 EeV. I will describe a recently proposed new mechanism that is in excellent accord with the constraints and observations. I will describe how it can be tested using UHECRs and GLAST.

Continue reading… UHECR Phenomenology – Glennys Farrar

We outline a dynamical dark energy scenario whose signatures may be simultaneously tested by astronomical observations and laboratory experiments. The dark energy is a field with slightly sub-gravitational couplings to matter, a logarithmic self- interaction potential with a scale tuned to ~ 10 -3 eV, as is usual in quintessence models, and an effective mass m phi influenced by the environmental energy density. Among the signatures of this scenario may be dark energy equation of state w is not equal to -1, stronger gravity in dilute mediums, that may influence BBN and appear as an excess of dark matter, and sub- millimeter corrections to Newton’s law,

Continue reading… Challenging the Cosmological Constant – Nemanja Kaloper

The talk will discuss the design and forecasting for measuring properties of Dark Energy and Dark Matter from new deep imaging surveys, in particular the “Dark Energy Survey” and the DUNE satellite. The effect of accuracy of photometric redshifts on the cosmological results will be assessed.

Continue reading… Observing Dark Energy with the Next Generation of Galaxy Surveys – Ofer Lahav

K-essence models – scalar field theories with non-quadratic kinetic terms – are considered candidates for dynamical dark energy and inflation. One of the most interesting features of these nonlinear theories is that perturbations around nontrivial backgrounds propagate with a speed different from the speed of light. In particular, superluminal propagation is possible. In my talk, I will review the k-essence paradigm emphasizing the issues related to causality. I will show that superluminal propagation does not lead to any additional causal paradoxes over and above those already present in standard general relativity. I will end by presenting a model which allows the obtaining of information from beyond the horizon of a black hole.

Continue reading… k-Essence: superluminal propagation, causality and emergent geometry – Alexander Vikman

The history of human knowledge is often highlighted by our efforts to explore beyond our apparent horizon. In this talk, I will describe how this challenge has now evolved into our quest to understand the physics at/beyond the cosmological horizon, some twenty orders of magnitude beyond Columbus’s original plan. I also argue why inflationary paradigm predicts the existence of non-trivial physics beyond the cosmological horizon, and how we can use the Integrated Sachs-Wolfe effect in the Cosmic Microwave Background to probe this physics, which includes the nature of gravity and primordial non-gaussianity on the horizon scale.

Continue reading… Physics Beyond the Horizon – Niayesh Afshordi

In the last two decades, cosmology has undergone a revolution, with a large influx of high quality data. There is now a consensus cosmological standard model, Lambda-CDM, based on General Relativity as the theory of gravity, and which requires only about 4% of the energy budget of the universe to be in known baryonic form. The rest is divided into two apparently distinct, dark components: Cold Dark Matter (CDM) and cosmological constant. The simplest explanation for CDM is a weakly interacting particle, still to be detected; he cosmological constant is the simplest term that can be added to the Einstein equations that can give rise to the observed accelerated expansion of the universe but has no compelling explanation within our current understanding of fundamental physics.

Continue reading… Demystifying the Large-Scale Structure and Evolution of the Cosmos – Constantinos Skordis

Recent developments have greatly extended our understanding of quantum gravity in cosmological environments. A new set of exact time-dependent solutions has been found to the equations of motion of string theory, that interpolate among string theories of dramatically different character. These transitions dynamically alter features of the theory such as the degree of stability, the amount of supersymmetry, the number of dimensions of space itself, and the basic type of string. Taken together, these transitions fill out a web that unifies (almost) all known string theories into a single dynamical structure.

Continue reading… Cosmological Unification of String Theories – Simeon Hellerman

The most remarkable recent discovery in fundamental physics is that the Universe is undergoing accelerated expansion. To achieve a proper understanding of its physical origin forces us to make a hard choice between dynamical and enviromental scenarios. The first approach predicts the existence of a new long distance physics in the gravitational sector, while the second relies on the existence of the vast landscape of vacua with different values of the cosmological constant. I will discuss achievements and shortcomings of each of the approaches, and illustrate them in the concrete examples.

Continue reading… The Accelerating Universe: Landscape or Modified Gravity? – Sergei Dubovsky

The late time behavior of decaying states is examined with regards to its deviation from the usual exponential form of decay. We will look at the origins of this well-established result in quantum mechanics and discuss the issues that arise in a field theory setting. An increase in the survival probability of a metastable state at large times finds applications in the context of cosmology, namely with regards to eternal inflation and the string theory landscape.

Continue reading… Late Time Behavior of False Vacuum Decay – James Dent

We present new constraints on the Hubble function H(phi) and subsequently on the inflationary scalar potential V(phi) from WMAP 3-year data combined with the Sloan Luminous Red Galaxy survey (SDSS-LRG), using a new methodology which appears to be more generic, conservative and model-independent than in most of the recent literature, since it depends neither on the slow-roll approximation, nor on any extrapolation scheme for the potential beyond the observable e-fold range, nor on additional assumptions about initial conditions for the inflaton velocity. Besides these new constraints, we will briefly discuss the accuracy of the slow-roll approximation in the light of present day observations,

Continue reading… What do WMAP and SDSS really tell about inflation? – Wessel Valkenburg

TBA

Continue reading… Bekenstein-Sanders theory of modified gravity – Constantinos Skordis

Evidence for Supermassive Black Holes at the centers of galaxy bulges, combined with the paradigm of hierarchical structure formation, implies the existence of binary Supermassive Black Holes. It is expected that these binaries themselves will eventually coalesce in what would be the brightest gravitational-radiation events in the astrophysical universe. In this talk, we discuss the effect of the overall galaxy merger rate as well as dynamical processes at the centers of galaxies that might effect this scenario, in particular the so-called “final parsec problem” indicating that a significant fraction of the binaries may stall before they can coalesce. I discuss the theoretical prospects for resolving this problem,

Continue reading… Gravitational Radiation from Supermassive Black Hole Binaries – Andrew Jaffe

The shapes of the primordial power spectra are the key quantities to unravel the physics of the inflationary epoch. We propose a new framework for parametrizing the spectra of primordial scalar and tensor perturbations, stressing the statistical trajectory nature of the relevant quantities and the importance of priors which can lead to spurious results like an apparent detection of tensor modes. We clarify the impact of prior probabilities, demonstrate strategies to adjust the prior distributions and as an example investigate a model inspired by high energy theory that exhibits intrinsic statistical elements.

Continue reading… Scanning Inflation – Pascal Vaudrevange

In light of recent findings which seem to disfavor a scenario with (warm) dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow (DW) mechanism, my colleagues and I investigated the constraints attainable for this mechanism by relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter. We firstly studied how to reinterpret the limits attainable from X-ray non-detection and Lyman-alpha forest measurements in the case that steril e neutrinos constitute only a fraction ‘f_s’ of the total amount of dark matter. Then, assuming that sterile neutrinos are generated in the early universe solely through the DW mechanism,

Continue reading… Sterile neutrinos as subdominant warm dark matter – Dan Cumberbatch

Explaining the predominance of visible matter over antimatter remains one of the outstanding puzzles at the interface of cosmology with particle and nuclear physics. Although the Standard Model cannot account for the matter-antimatter asymmetry, new physics at the electroweak scale may provide the solution. In this talk, I discuss the general requirements for successful electroweak scale baryogenesis; recent theoretical work in computations of the matter-antimatter asymmetry; and implications for experimental searches for permanent electric dipole moments of the electron and neutron and for the Higgs boson at future colliders.

Continue reading… Baryogenesis, Electric Dipole Moments, and the Higgs Boson – Michael Ramsey-Musolf

Accelerometer measurments indicate that a circular field is induced when the rotation rate of a Niobium superconducting ring changes. If found to be genuine, this would be the first-ever gravitational-like field induced by controllable means. The field is measured inside the ring and its magnitude and direction opposes the ring’s angular acceleration. Since this observation does not match any theory, the emphasis is to carefully verify the observations. This seminar will describe the observations, experimental methods, and next-step options. This includes data from independent experiments conducted at the University of Canterbury, NZ, where the world’s most accurate ring-laser-gyro was used to search for the noted effects,

Continue reading… Gravitational Breakthrough or Experimental Error? – Martin Tajmar

The origin of the highest energy cosmic rays has remained a persistent mystery for decades. Now we seem to be on the verge of getting a new handle on where in the universe these things come from. The Pierre Auger Observatory has been operating since 2004, and already we have some clear clues, including the energy spectrum and limits on photon flux that strongly suggest an extragalactic origin for the highest energy cosmic rays. More recently the unparalleled collecting area of Auger has been brought to bear on the question of potential correlations between particular astrophysical objects and cosmic ray arrival directions.

Continue reading… Extragalatic Cosmic Rays: a Prescription to Avoid Disaster – Corbin Covault

The standard model of cold dark matter predicts the existence of thousands of small dark matter halos orbiting the Milky Way, and steep cusps in the central regions of dark matter halos. The low-luminosity, dark matter dominated dwarf galaxy population of the Milky Way provides an ideal laboratory for testing these predictions, and thus placing strong constraints on the nature of dark matter. I will show how present kinematic data from the galaxies tests solutions to the CDM ‘missing satellites problem,’ and how future astrometric data will reveal the presence of central density cores or cusps. I will also discuss how the kinematic data from these galaxies is able to provide strong constraints on the signal from cold dark matter particles annihilating into gamma-rays,

Continue reading… Dark matter, small-scale structure, and dwarf galaxies – Louie Strigari