Edward W. Kolb

Report of the Dark Energy Task Force

Dark energy appears to be the dominant component of the physical Universe, yet there is no persuasive theoretical explanation for its existence or magnitude. The acceleration of the Universe is, along with dark matter, the observed phenomenon that most directly demonstrates that our theories of fundamental particles and gravity are either incorrect or incomplete. Most experts believe that nothing short of a revolution in our understanding of fundamental physics will be required to achieve a full understanding of the cosmic acceleration. For these reasons, the nature of dark energy ranks among the very most compelling of all outstanding problems in physical science. These circumstances demand an ambitious observational program to determine the dark energy properties as well as possible.

Cosmological problems for the polonyi potential

We study the cosmological implications of N = 1 supergravity with the Polonyi potential. We find that for typical values of the gravitino mass (102-103 GeV) the universe goes through a late period of reheating (i.e., from a temperature of about 10 -7 MeV to 10 -2 MeV). Any baryon-to-photon ratio is thus diluted by an unacceptable 15 orders of magnitude, with no hope of regeneration.

Maverick dark matter at colliders

Assuming that dark matter is a weakly interacting massive particle (WIMP) species X produced in the early Universe as a cold thermal relic, we study the collider signal of pp or

Largest temperature of the radiation era and its cosmological implications

p\bar{p} \rightarrow \bar{X}X

Baryon number generation in the early universe

+ jets and its distinguishability from standard-model background processes associated with jets and missing energy. We assume that the WIMP is the sole particle related to dark matter within reach of the LHC — a “maverick” particle — and that it couples to quarks through a higher dimensional contact interaction. We simulate the WIMP final-state signal

Solutions to the strong CP problem in a world with gravity

X\bar{X}

Superheavy dark matter

+ jets and dominant standard-model (SM) background processes and find that the dark-matter production process results in higher energies for the colored final state partons than do the standard-model background processes. As a consequence, the detectable signature of maverick dark matter is an excess over standard-model expectations of events consisting of large missing transverse energy, together with large leading jet transverse momentum and scalar sum of the transverse momenta of the jets. Existing Tevatron data and forthcoming LHC data can constrain (or discover!) maverick dark matter.

On cosmic acceleration without dark energy

The thermal history of the universe before the epoch of nucleosynthesis is unknown. The maximum temperature in the radiation-dominated era, which we will refer to as the reheat temperature, may have been as low as 0.7 MeV. In this paper we show that a low reheat temperature has important implications for many topics in cosmology. We show that weakly interacting massive particles (WIMPs) may be produced even if the reheat temperature is much smaller than the freeze-out temperature of the WIMP, and that the dependence of the present abundance on the mass and the annihilation cross section of the WIMP differs drastically from familiar results. We revisit predictions of the relic abundance and resulting model constraints of supersymmetric dark matter, axions, massive neutrinos, and other dark matter candidates, nucleosynthesis constraints on decaying particles, and leptogenesis by decay of superheavy particles. We find that the allowed parameter space of supersymmetric models is altered, removing the usual bounds on the mass spectrum; the cosmological bound on massive neutrinos is drastically changed, ruling out Dirac (Majorana) neutrino masses

Production of massive particles during reheating

m_\nu

Probing Planckian physics: Resonant production of particles during inflation and features in the primordial power spectrum

only in the range 33 keV