College of Arts and Sciences

Astrophysical Neutrinos: Revealing Neutrino Properties at the Highest Energies

Continue reading… Michelson Postdoctoral Prize Lecture – Nicole Bell

I discuss the backreaction of inhomogeneities on the expansion of the universe. The average behaviour of an inhomogeneous spacetime is not given by the Friedmann-Robertson-Walker equations. The new terms in the exact equations hold the possibility of explaining the observed acceleration without a cosmological constant or new physics. In particular, the coincidence problem may be solved by a connection with structure formation.

Continue reading… Accelerated expansion from structure formation – Syksy Rasanen

The unique properties of scintillation light in liquid neon and liquid argon make possible conceptually simple, massive, and highly sensitive detectors of low-energy solar neutrinos and cosmological dark matter. I will describe the program underway for the design and construction of two novel and complementary detectors dubbed DEAP (Dark matter Experiment with Argon and Pulse shape discrimination) and CLEAN (Cryogenic Low Energy Astrophysics with Neon).

Continue reading… DEAP and CLEAN Detectors for Low-Energy Particle Astrophysics – Andrew Hime

In recent years, we have learned a great deal about dark matter, but are still ignorant of its identity. The key to uncovering this mystery is likely to lie in some combination of direct and indirect detection techniques, as well as with collider experiments. In this talk, I will explore the ability of indirect detection experiments using anti-matter, neutrinos and gamma-rays to detect particle dark matter. I will summarize the current observational situation and project the reach of these endeavors in the coming years.

Continue reading… In Search of Particle Dark Matter – Dan Hooper

The ongoing Sloan Digital Sky Survey (SDSS) is providing a wealth of information enabling extensive large-scale structure studies. I will present measurements of galaxy clustering with the SDSS redshift survey, using a sample of about 200,000 galaxies, and concentrating on the two-point correlation function. The SDSS is particularly suitable for investigating the dependence of clustering on galaxy properties, and we focus on the dependence on color and on luminosity. We interpret the measurements using contemporary models of galaxy clustering, which help to elucidate the features of the observed correlation functions and provide insights on galaxy formation and the relation of galaxies and dark matter.

Continue reading… Galaxy Clustering in the SDSS Redshift Survey – Idit Zehavi

I will discuss results from recent studies on production of radioisotopes by muon-induced showers in neutrino detectors located deep underground. Cosmogenic radioisotopes represent one of the most significant and important classes of background for experiments on solar neutrinos. I will show how a detailed understanding of the production mechanisms of the radioisotopes can help in opening new windows of observation for low energy solar neutrinos (in particular, pep neutrinos). I will also review the status and the plans for the WARP experiment at Gran Sasso. WARP is a two-phase argon drift chamber designed for direct detection of WIMP Dark Matter.

Continue reading… Cosmogenic Radioisotopes in Low Background Experiments – The WARP Experiment at Gran Sasso – Cristiano Galbiati

Motivated by the interpretation of the recent results on the TeV gamma radiation from the Galactic center, including the new 2004 HESS data, as a by-product of dark matter particles annihilations, we address the question of the largest possible neutralino masses and pair annihilation cross sections in supersymmetric models. Extending the parameter space of minimal models, such as the mSUGRA and the mAMSB scenarios, to general soft SUSY breaking Higgs masses gives access to the largest possible pair annihilation rates, corresponding to resonantly annihilating neutralinos with maximal gaugino-higgsino mixing. Adopting a model-independent approach, we provide analytical and numerical upper limits for the neutralino pair annihilation cross section.

Continue reading… TeV gamma-rays and the largest masses and annihilation cross sections of neutralino dark matter – Stefano Profumo

Nearly 150 extrasolar planets have been discovered to date, and their observed orbits display an unexpected diversity. This talk considers a collection of processes for planet migration and orbital evolution, including those operating on a range of time scales. In particular, we consider planet-planet scattering, the action of disk torques, scattering of solar systems with passing binary star systems, and the long term evolution of planetary systems. The result of this survey of processes provides a explanation for the orbital elements of observed planetary systems, places constraints on the birth aggregate of our solar system, and determines the fraction of binary star systems that allow for the long term stability of an Earth-like planet.

Continue reading… Chaotic Processes in Planet Migration and Orbital Evolution – Fred Adams

Coherent neutral current neutrino-nucleus elastic scattering has never been observed. Although the cross-section is very high, nuclear recoil energies are very small. However, detection of the process may be possible for the new generation of low-threshold detectors. A promising prospect for the first detection of this process is an experiment at a high flux stopped-pion neutrino source such as the SNS. I will present some preliminary rate calculations and discuss the physics reach of such an experiment.

Continue reading… Prospects for Measuring nu-N Coherent Scattering at a Spallation Source

We review the inclusion of dark energy into the formalism of spherical collapse, and the virialization of a two-component system, made of matter and dark energy. We compare two approaches in the literature. The first assumes that only the matter component virializes, e.g. as in the case of a classic cosmological constant. The second approach allows the full system to virialize as a whole. We show that the two approaches give fundamentally different results for the final state of the system. This might be a differentiating signature between the classic cosmological constant which cannot virialize, and a dynamical dark energy mimicking a cosmological constant.

Continue reading… On virialization with dark energy – Irit Maor

Coherent neutral current neutrino-nucleus elastic scattering has never been observed. Although the cross-section is very high, nuclear recoil energies are very small. However, detection of the process may be possible for the new generation of low-threshold detectors. A promising prospect for the first detection of this process is an experiment at a high flux stopped-pion neutrino source such as the SNS. I will present some preliminary rate calculations and discuss the physics reach of such an experiment.

Continue reading… Prospects for Measuring nu-N Coherent Scattering at a Spallation Source – Kate Scholberg

We show that violation of the null energy condition implies instability in a broad class of models, including classical gauge theories with scalar and fermionic matter as well as any perfect fluid. When applied to the dark energy, our results imply that w = p / rho is unlikely to be less than -1. As another application, Lorentzian (traversable) wormholes and time machines with semi-classical spacetimes are unstable to small perturbations.

Continue reading… Wormholes, Dark Energy, and the Null Energy Condition – Roman Buniy

It has been argued that neutrinos originating from ultra-high energy cosmic rays produce black holes deep in the atmosphere in models with TeV-scale quantum gravity. Such black holes would initiate quasi-horizontal showers of particles far above the standard model rate, so that the Auger Observatory would observe hundreds of black hole events. This would provide the first opportunity for experimental study of microscopic black holes. However, any phenomenologically viable model with a low scale of quantum gravity must explain how to preserve protons from rapid decay mediated by virtual black holes. We argue that unless this is accomplished by the gauging of baryon or lepton number,

Continue reading… Can black hole events from cosmic rays be observed at the Auger Observatory? – Dejan Stojkovic

It is expected that a number of quantum aspects of the gravitational field and its interaction with the remaining matter fields can be studied within a low-energy effective field theory approach provided that the typical scales involved are much larger than the Planck length. This has been considered in some detail for weak gravitational fields, but physically interesting situations often involve strong fields. Some non-equilibrium field theory methods which are particularly useful to address gravitational back reaction problems, such as the closed time path (CTP) formalism, will be briefly reviewed. I will then explain how to extract information on metric fluctuations and discuss applications to black hole and cosmological spacetimes.

Continue reading… Quantum metric fluctuations in cosmological and black hole spacetimes – Albert Roura

Although a discovery of wimps either at colliders or indirect experiments would have enormous implications for our understanding of particle physics, it would imply less than one would like about our understanding of the dark matter in the universe or in the galactic halo: it surely is possible that discovered particles account for only a little of the total dark matter. To establish the cosmological significance of a wimp discovery, their density must be determined. I will show that data from neither hadron colliders nor direct detection experiments alone can be sufficient to determine the local or relic density of discovered wimps,

Continue reading… What is the Cosmological Significance of a Discovery of Wimps at Colliders or in Direct Experiments? – Jacob Bourjaily