arXiv subjects

Josef Pradler

Publications and source records attributed to Josef Pradler.

At least 73 records · Page 4Linked to original sources

arXiv2013

Dark Matter or Neutrino recoil? Interpretation of Recent Experimental Results

The elastic nuclear recoil signal, being under intense scrutiny by multiple underground experiments, can be interpreted either as coming from the interaction of nuclei with WIMP dark matter or from the scattering of new species of MeV-energy neutrinos. The most promising model for the latter case is a neutrino $ν_b$ that interacts with baryon number, and with a flux sourced by the oscillations of regular solar $^8$B neutrinos. We re-analyze this model in light of the latest experimental results. In contrast to the light-DM interpretation of various tentative positive signals (anomalies) that is now seriously challenged by the negative results of the LUX experiment, the neutrino interpretation remains a viable explanation to most of the anomalies. Considering future prospects, we show that the superCDMS experiment alone, when equipped with Ge and Si detectors, will be able to detect $ν_b$ and discriminate the model from a light DM interpretation. In addition, we also provide the forecast for the new CRESST-II run that now operates with new detectors and diminished backgrounds.

hep-ph↗

arXiv2013

New Light on Dark Photons

"Dark Photons", light new vector particles V kinetically mixed with the photon, are a frequently considered extension of the Standard Model. For masses below 10 keV they are emitted from the solar interior. In the limit of small mass m_V the dark photon flux is strongly peaked at low energies and we demonstrate that the constraint on the atomic ionization rate imposed by the results of the XENON10 Dark Matter experiment sets the to-date most stringent limit on the kinetic mixing parameter of this model: κ*m_V < 3*10^{-12} eV. The result significantly improves previous experimental bounds and surpasses even the most stringent astrophysical and cosmological limits in a seven-decade-wide interval of m_V.

hep-ph↗

arXiv2013

New stellar constraints on dark photons

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 κand m_V are the mixing angle with the photon and the mass of the dark state. This is in contrast with earlier erroneous claims 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 red giant 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.

hep-ph↗

arXiv2013

Dark Matter Detectors as Dark Photon Helioscopes

Light new particles with masses below 10 keV, often considered as a plausible extension of the Standard Model, will be emitted from the solar interior, and can be detected on the Earth with a variety of experimental tools. Here we analyze the new "dark" vector state V, a massive vector boson mixed with the photon via an angle kappa, that in the limit of the small mass m_V has its emission spectrum strongly peaked at low energies. Thus, we utilize the constraints on the atomic ionization rate imposed by the results of the XENON10 experiment to set the limit on the parameters of this model: kappa times m_V< 3 times10^{-12} eV. This makes low-threshold Dark Matter experiments the most sensitive dark vector helioscopes, as our result not only improves current experimental bounds from other searches by several orders of magnitude, but also surpasses even the most stringent astrophysical and cosmological limits in a seven-decade-wide interval of m_V. We generalize this approach to other light exotic particles, and set the most stringent direct constraints on "mini-charged" particles.

hep-ph↗

arXiv2013

Elastic scattering signals of solar neutrinos with enhanced baryonic currents

The coupling of the baryonic current to new neutrino states ν_b with strength in excess of the weak interactions is a viable extension of the Standard Model. We analyze the signature of ν_b appearance in the solar neutrino flux that gives rise to an elastic scattering signal in dark matter direct detection and in solar neutrino experiments. This paper lays out an in-depth study of ν_b detection prospects for current and future underground rare event searches. We scrutinize the model as a possible explanation for the reported anomalies from DAMA, CoGeNT, and CRESST-II and confront it with constraints from other null experiments.

hep-ph↗

arXiv2013

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

The rate of the direct decay of 40K to the ground state of 40Ar 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 10ppb contamination of natural potassium requires a 20% modulation fraction or more. A 20ppb 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 40K decays as inferred from simulation. We propose measures to help clarify the situation.

hep-ph↗

arXiv2013

Addendum to "On an unverified nuclear decay and its role in the DAMA experiment''

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 DAMA's recent comment our claim is further corroborated. We identify the source of the discrepancy between our own analysis and DAMA's claimed levels of unmodulated background. Our analysis indicates that the background in the signal region as reported by DAMA is indeed likely underestimated.

hep-ph↗

arXiv2013

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, 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 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.

hep-ph↗

arXiv2012

On the Cosmic Ray Muon Hypothesis for DAMA

The DAMA dark matter search experiment observes a statistically significant percent-level variation of its low-energy count rate with a period of one year. In this note we recall some of the arguments which challenge the hypothesis that the cosmic ray induced underground muon flux can be the origin of the modulation. In addition, we provide new comments on recent works on this subject.

hep-ph↗

arXiv2012

Statistical Tests of Noise and Harmony in Dark Matter Modulation Signals

The aim of the current work is a detailed time-series analysis of the data from Dark Matter direct detection experiments as well as related datasets. We examine recent claims that the cosmic ray muon flux can be responsible for generating the modulation signals seen by DAMA and, more recently, by the CoGeNT collaboration. We find no evidence for such a strong correlation and show that the two phenomena differ in their power spectrum, phase, and possibly in amplitude. In addition, we investigate in more detail, the time dependence of Dark Matter scattering. Since the signal is periodic with period of a year (due to the Earth's motion around the Sun), the presence of higher harmonics can be expected. We show that the higher harmonics generically have similar phase to the annual modulation and the biannual mode in particular could provide another handle in searching for Dark Matter in the laboratory.

hep-ph↗

arXiv2011

Dark Matter from Minimal Flavor Violation

We consider theories of flavored dark matter, in which the dark matter particle is part of a multiplet transforming nontrivially under the flavor group of the Standard Model in a manner consistent with the principle of Minimal Flavor Violation (MFV). MFV automatically leads to the stability of the lightest state for a large number of flavor multiplets. If neutral, this particle is an excellent dark matter candidate. Furthermore, MFV implies specific patterns of mass splittings among the flavors of dark matter and governs the structure of the couplings between dark matter and ordinary particles, leading to a rich and predictive cosmology and phenomenology. We present an illustrative phenomenological study of an effective theory of a flavor SU(3)_Q triplet, gauge singlet scalar.

hep-ph↗

arXiv2011

Primordial beryllium as a big bang calorimeter

Many models of new physics including variants of supersymmetry predict metastable long-lived particles that can decay during or after primordial nucleosynthesis, releasing significant amounts of non-thermal energy. The hadronic energy injection in these decays leads to the formation of ^9Be via the chain of non-equilibrium transformations: Energy_h -> T, ^3He -> ^6He, ^6Li -> ^9Be. We calculate the efficiency of this transformation and show that if the injection happens at cosmic times of a few hours, the release of 10 MeV per baryon can be sufficient for obtaining a sizable ^9Be abundance. The absence of a plateau-structure in the ^9Be/H abundance down to a 10^{-14} level allows one to use beryllium as a robust constraint on new physics models with decaying or annihilating particles.

astro-ph.CO↗

arXiv2011

Non-Abelian Discrete Dark Matter

We consider the minimal model in which dark matter is stabilized by a non-Abelian discrete symmetry. The symmetry group is taken to be D_3, which is the smallest non-Abelian finite group. The minimal model contains (nontrivial) singlet and doublet scalar representations of D_3 which couple to the Standard Model fields via the Higgs portal. This construction predicts two species of dark matter over much of the parameter space. Nontrivial interactions under D_3 lead to a novel thermal history of dark matter, while the multi-component nature of dark matter can be tested by future direct detection experiments.

hep-ph↗

arXiv2010

Big Bang Nucleosynthesis as a Probe of New Physics

Big bang nucleosynthesis (BBN), an epoch of primordial nuclear transformations in the expanding Universe, has left an observable imprint in the abundances of light elements. Precision observations of such abundances, combined with high-accuracy predictions, provide a nontrivial test of the hot big bang and probe non-standard cosmological and particle physics scenarios. We give an overview of BBN sensitivity to different classes of new physics: new particle or field degrees of freedom, time-varying couplings, decaying or annihilating massive particles leading to non-thermal processes, and catalysis of BBN by charged relics.

hep-ph↗

arXiv2010

Metastable GeV-scale particles as a solution to the cosmological lithium problem

The persistent discrepancy between observations of 7Li with putative primordial origin and its abundance prediction in Big Bang Nucleosynthesis (BBN) has become a challenge for the standard cosmological and astrophysical picture. We point out that the decay of GeV-scale metastable particles X may significantly reduce the BBN value down to a level at which it is reconciled with observations. The most efficient reduction occurs when the decay happens to charged pions and kaons, followed by their charge exchange reactions with protons. Similarly, if X decays to muons, secondary electron antineutrinos produce a similar effect. We consider the viability of these mechanisms in different classes of new GeV-scale sectors, and find that several minimal extensions of the Standard Model with metastable vector and/or scalar particles are capable of solving the cosmological lithium problem. Such light states can be a key to the explanation of recent cosmic ray anomalies and can be searched for in a variety of high-intensity medium-energy experiments.

hep-ph↗

arXiv2009

The long-lived stau as a thermal relic

We consider physics beyond the Standard Model in which a long-lived electromagnetically charged massive particle species (CHAMP) appears. We discuss the unique sensitivity the early Universe exhibits on the mere presence and on the decay of such a particle. A CHAMP can be realized in supersymmetric extensions of the Standard Model. We carry out a detailed study of gravitino dark matter scenarios in which the lighter stau is the lightest Standard Model superpartner and thus the CHAMP. Particularly stringent constraints on the gravitino-stau scenario arise from the thermal catalysis of primordial nucleosynthesis reactions. This motivates a thorough investigation of the thermal freeze-out process of the long-lived stau. There, we show that even the most stringent cosmological constraints can potentially be evaded.

hep-ph↗

arXiv2008

Constraints on Supersymmetric Models from Catalytic Primordial Nucleosynthesis of Beryllium

The catalysis of nuclear reactions by negatively charged relics leads to increased outputs of primordial ^6Li and ^9Be. In combination with observational constraints on the primordial fractions of ^6Li and ^9Be, this imposes strong restrictions on the primordial abundance and the lifetime of charged relics. We analyze the constraints from the catalysis of ^9Be on supersymmetric models in which the gravitino is the lightest supersymmetric particle and a charged slepton--such as the lighter stau--the next-to-lightest supersymmetric particle (NLSP). Barring the special cases in which the primordial fraction of the slepton NLSP is significantly depleted, we find that the ^9Be data require a slepton NLSP lifetime of less than 6x10^3 seconds. We also address the issue of the catalytic destruction of ^6Li and ^9Be by late forming bound states of protons with negatively charged relics finding that it does not lead to any significant modification of the limit on the slepton lifetime.

hep-ph↗

arXiv2008

Thermal relic abundances of long-lived staus

In supersymmetric models with a long-lived stau being the lightest Standard Model superpartner, the stau abundance during primordial nucleosynthesis is tightly constrained. Considering the complete set of stau annihilation channels in the minimal supersymmetric Standard Model (MSSM) with real parameters for scenarios in which sparticle coannihilations are negligible, we calculate the decoupling of the lighter stau from the primordial plasma and identify processes which are capable to deplete the resulting stau abundance significantly. We find particularly efficient stau annihilation at the resonance of the heavy CP-even Higgs boson and for a lighter stau with a sizeable left-right mixing due to enhanced stau-Higgs couplings. Even within the constrained MSSM, we encounter both effects leading to exceptionally small values of the resulting stau abundance. Prospects for collider phenomenology are discussed and possible implications of our findings are addressed with emphasis on gravitino dark matter scenarios.

hep-ph↗