Particle Physics

Recent experimental results seem to require a dramatic change in our view of the dark matter sector. In this talk I will describe the reasons for this change and the ingredients required to describe the new data. I will present possible field theories that give rise to such phenomena and delineate the resulting collider signatures.

Recent PAMELA and ATIC results may represent a breakthrough in dark matter searches beyond its gravitational imprint. After briefly reviewing the possible (classes of) explanations for the observed excesses in positron and electron cosmic ray fluxes I will focus on a two component dark matter model that may provide an explanation for large boost factors needed in the dark matter annihilation interpretation of the signals.

The interpretation of virtual gluons as ghosts in the non-linear gluonic structure of QCD permits the formulation and realization of a manifestly gauge-invariant and Lorentz covariant theory of interacting quarks/antiquarks, for all values of coupling. The simplest example of quark/antiquark scattering in a high-energy, quenched, eikonal model at large coupling is shown to be expressable as a set of finite, local integrals which may be evaluated numerically; and before evaluation, it is clear that the result will be dependent only on, and damped by increasing momentum transfer, while displaying physically-reasonable color dependence in a manner underlying the MIT Bag Model and an effective, asymptotic freedom. These results are compatible with an earlier, instanton, field-strength analysis of Reinhardt, et.al.

New low frequency radio telescopes currently being built open up the possibility of observing the 21 cm radiation before the Epoch of Reionization in the future, in particular at redshifts 200 ≥ z ≥ 30, also known as the dark ages. At these high redshifts, Cosmic Microwave Back-ground (CMB) radiation is absorbed by neutral hydrogen at its 21 cm hyperfine transition. This redshifted 21 cm signal thus carries information about the state of the early Universe and can be used to test fundamental physics. We study the constraints these observations can put on the variation of fundamental constants and on fundamental mass scales. We show that the 21 cm radiation is very sensitive to the variations in the fine structure constant and can in principle place constraints comparable to or better than the other astrophysical experiments. Cosmic strings, if they exist, contribute to the anisotropies in the primordial gas leaving an imprint on the 21 cm radiation. They can tell us about the fundamental mass scales involved in the theories beyond the standard model. We show that the 21 cm radiation can potentially probe cosmic strings of tension ~10−12 asumming intercommutation probability of 1. Making such observations will require radio telescopes of collecting area 10 − 106 km2 compared to ~ 1 km2 of current telescopes.

Precision tests of Local Position Invariance (LPI) involve many different methods in atomic, nuclear and gravitational physics, astrophysics and cosmology, and many different epochs and environments. We present some methods for comparing or combining different methods, either in a model-independent way or within simple scalar field models of variation. We focus on which methods are most sensitive to cosmologically recent time variation, and also on tests of spatial variation within the Solar System.

I will describe a method of understanding how the nuclear binding energies depend on the masses of the light quarks. This is useful in applications ranging from anthropic constraints to equivalence principle tests and bounds on the time variation on the quark masses.

To date, optical clocks based on singly trapped ions1) and ultracold neutral atoms trapped in the Stark-shift-free optical lattices2) are regarded as promising candidates for future atomic clocks. So far “optical lattice clocks” have been evaluated with uncertainty of 1×10-15 (ref. 3)) limited by that of Cs atomic clocks. Frequency comparison between highly-stable and accurate optical lattice clocks is, therefore, crucial for their further evaluation. Looking toward fractional uncertainties of 10-16 and below, collisional frequency shift, Black body radiation (BBR) shift, and hyperpolarizability effects, all of which depend on interrogated atomic elements and experimental configurations, are becoming major concerns. In this talk, we discuss optimal lattice geometries in view of the quantum statistics and related spins of interrogated atoms. This leads to two promising configurations for the lattice clock: One-dimensional (1D) lattice loaded with spin-polarized fermions4) and 3D lattice loaded with bosons. We present frequency comparison of these two optical lattice clocks using fermionic 87Sr and bosonic 88Sr. Such lattice clock comparison will offer an important step to ascertain the clocks’ uncertainty beyond the Cs limit of 1×10-15. As for the latter two issues, the BBR and the lattice laser related uncertainties, we discuss prospects for a cryogenic clock, a “blue-detuned” magic wavelength, and a Hg based optical lattice clock5). References: 1) T. Rosenband et al., Science 319 (2008) 1808. 2) H. Katori, M. Takamoto, V. G. Pal\'chikov and V. D. Ovsiannikov, Phys. Rev. Lett. 91 (2003) 173005. 3) S. Blatt et al., Phys. Rev. Lett. 100 (2008) 140801. 4) M. Takamoto et al., J. Phys. Soc. Jpn. 75 (2006) 104302

We propose new experiments with high sensitivity to a possible variation of the electron-to-proton mass ratio µ me/mp. We consider a nearly degenerate pair of molecular vibrational levels, each associated with a different electronic potential. With respect to a change in µ, the change in the splitting between such levels can be large both on an absolute scale and relative to the splitting. We demonstrate the existence of such pairs of states in Cs2, where the narrow spectral lines achievable with ultracold molecules make the system promising for future searches for small variations in µ.