Josef Pradler

New stellar constraints on dark photons

Abstract We consider the stellar production of vector states V within the minimal model of “dark photons”. We show that when the Stuckelberg mass of the dark vector becomes smaller than plasma frequency, the emission rate is dominated by the production of the longitudinal modes of V, and scales as κ 2 m V 2 , where κ and m V are the mixing angle with the photon and the mass of the dark state. This is in contrast with widespread assertions in the literature that the emission rate decouples as the forth power of the mass. We derive ensuing constraints on the ( κ , m V ) parameter space by calculating the cooling rates for the Sun and horizontal branch stars. We find that stellar bounds for m V 10 eV are significantly strengthened, to the extent that all current “light-shining-through-wall” experiments find themselves within deeply excluded regions.

Direct detection constraints on dark photon dark matter

Dark matter detectors built primarily to probe elastic scattering of WIMPs on nuclei are also precise probes of light, weakly coupled, particles that may be absorbed by the detector material. In this paper, we derive constraints on the minimal model of dark matter comprised of long-lived vector states V (dark photons) in the 0.01–100 keV100 keV mass range. The absence of an ionization signal in direct detection experiments such as XENON10 and XENON100 places a very strong constraint on the dark photon mixing angle, down to O(10^(−15)), assuming that dark photons comprise the dominant fraction of dark matter. This sensitivity to dark photon dark matter exceeds the indirect bounds derived from stellar energy loss considerations over a significant fraction of the available mass range. We also revisit indirect constraints from V→3γ decay and show that limits from modifications to the cosmological ionization history are comparable to the updated limits from the diffuse γ-ray flux.

On an unverified nuclear decay and its role in the DAMA experiment

The rate of the direct decay of K40 to the ground state of Ar40 through electron capture has not been experimentally reported. Aside from its inherent importance for the theory of electron capture as the only such decay known of its type (unique third-forbidden), this decay presents an irreducible background in the DAMA experiment. We find that the presence of this background, as well as others, poses a challenge to any interpretation of the DAMA results in terms of a Dark Matter model with a small modulation fraction. A 10 ppb contamination of natural potassium requires a 20% modulation fraction or more. A 20 ppb contamination, which is reported as an upper limit by DAMA, disfavors any Dark Matter origin of the signal. This conclusion is based on the efficiency of detecting K40 decays as inferred from simulation. We propose measures to help clarify the situation.

Room for New Physics in the Rayleigh-Jeans Tail of the Cosmic Microwave Background

Maxim Pospelov, 2, 3 Josef Pradler, Joshua T. Ruderman, 3 and Alfredo Urbano 3 Perimeter Institute for Theoretical Physics, 31 Caroline Street N, Waterloo, Ontario N2L 2Y5, Canada Department of Physics and Astronomy, University of Victoria, Victoria, BC V8P 5C2, Canada Theoretical Physics Department, CERN, Geneva, Switzerland Institute of High Energy Physics, Austrian Academy of Sciences, Nikolsdorfergasse 18, 1050 Vienna, Austria Center for Cosmology and Particle Physics, Department of Physics, New York University, New York, NY 10003, USA INFN, sezione di Trieste, SISSA, via Bonomea 265, 34136 Trieste, Italy (Dated: September 14, 2018)

Addendum to “On an unverified nuclear decay and its role in the DAMA experiment” [Phys. Lett. B 720 (4–5) (2013) 399–404]

We reply to the critiques of our paper arXiv:1210.5501 by the DAMA collaboration which appeared in arXiv:1210.6199 and arXiv:1211.6346. Our original claim that the observed background levels are likely to require a large modulation fraction of any putative signal holds. In fact, in light of DAMAs recent comment our claim is further corroborated. We identify the source of the discrepancy between our own analysis and DAMAs claimed levels of unmodulated background. Our analysis indicates that the background in the signal region as reported by DAMA is indeed likely underestimated.

Direct constraints on charged excitations of dark matter.

If the neutral component of weak-scale dark matter is accompanied by a charged excitation separated by a mass gap of less than ~20 MeV, weakly interacting massive particles (WIMPs) can form stable bound states with nuclei. We show that the recent progress in experiments searching for neutrinoless double-beta decay sets the first direct constraint on the exoergic reaction of WIMP-nucleus bound state formation. We calculate the rate for such a process in representative models and show that the double-beta decay experiments provide unique sensitivity to a large fraction of parameter space of the WIMP doublet model, complementary to constraints imposed by cosmology and direct collider searches.