A new life for sterile neutrino dark matter after the pandemic

We propose a novel mechanism to generate sterile neutrinos $\nu_s$ in theearly Universe, by converting ordinary neutrinos $\nu_\alpha$ in scatteringprocesses $\nu_s\nu_\alpha\to\nu_s\nu_s$. After initial production byoscillations, this leads to an exponential growth in the $\nu_s$ abundance. Weshow that such a production regime naturally occurs for self-interacting$\nu_s$, and that this opens up significant new parameter space where $\nu_s$make up all of the observed dark matter. Our results provide strong motivationto further push the sensitivity of X-ray line searches, and to improve onconstraints from structure formation.<br

A new life for sterile neutrino dark matter after the pandemic

We propose a novel mechanism to generate sterile neutrinos $\nu_s$ in theearly Universe, by converting ordinary neutrinos $\nu_\alpha$ in scatteringprocesses $\nu_s\nu_\alpha\to\nu_s\nu_s$. After initial production byoscillations, this leads to an exponential growth in the $\nu_s$ abundance. Weshow that such a production regime naturally occurs for self-interacting$\nu_s$, and that this opens up significant new parameter space where $\nu_s$make up all of the observed dark matter. Our results provide strong motivationto further push the sensitivity of X-ray line searches, and to improve onconstraints from structure formation.<br

A new life for sterile neutrino dark matter after the pandemic

We propose a novel mechanism to generate sterile neutrinos $\nu_s$ in the early Universe, by converting ordinary neutrinos $\nu_\alpha$ in scattering processes $\nu_s\nu_\alpha\to\nu_s\nu_s$. After initial production by oscillations, this leads to an exponential growth in the $\nu_s$ abundance. We show that such a production regime naturally occurs for self-interacting $\nu_s$, and that this opens up significant new parameter space where $\nu_s$ make up all of the observed dark matter. Our results provide strong motivation to further push the sensitivity of X-ray line searches, and to improve on constraints from structure formation

Implications of unitarity and gauge invariance for simplified dark matter models

We show that simplified models used to describe the interactions of dark matter with Standard Model particles do not in general respect gauge invariance and that perturbative unitarity may be violated in large regions of the parameter space. The modifications necessary to cure these inconsistencies may imply a much richer phenomenology and lead to stringent constraints on the model. We illustrate these observations by considering the simplified model of a fermionic dark matter particle and a vector mediator. Imposing gauge invariance then leads to strong constraints from dilepton resonance searches and electroweak precision tests. Furthermore, the new states required to restore perturbative unitarity can mix with Standard Model states and mediate interactions between the dark and the visible sector, leading to new experimental signatures such as invisible Higgs decays. The resulting constraints are typically stronger than the ‘classic’ constraints on DM simplified models such as monojet searches and make it difficult to avoid thermal overproduction of dark matter

The Gravitino-Stau Scenario after Catalyzed BBN

We consider the impact of Catalyzed Big Bang Nucleosynthesis on theories with a gravitino LSP and a charged slepton NLSP. In models where the gravitino to gaugino mass ratio is bounded from below, such as gaugino-mediated SUSY breaking, we derive a lower bound on the gaugino mass parameter m_1/2. As a concrete example, we determine the parameter space of gaugino mediation that is compatible with all cosmological constraints.Comment: 1+14 pages, 6 figures; v2: minor clarifications, 1 reference added, matches version to appear in JCA

A precision study of the fine tuning in the DiracNMSSM

Recently the DiracNMSSM has been proposed as a possible solution to reduce the fine tuning in supersymmetry. We determine the degree of fine tuning needed in the DiracNMSSM with and without non-universal gaugino masses and compare it with the fine tuning in the GNMSSM. To apply reasonable cuts on the allowed parameter regions we perform a precise calculation of the Higgs mass. In addition, we include the limits from direct SUSY searches and dark matter abundance. We find that both models are comparable in terms of fine tuning, with the minimal fine tuning in the GNMSSM slightly smaller.Comment: 20 pages + appendices, 10 figure

Dark Matter Direct Detection with Non-Maxwellian Velocity Structure

The velocity distribution function of dark matter particles is expected to show significant departures from a Maxwell-Boltzmann distribution. This can have profound effects on the predicted dark matter - nucleon scattering rates in direct detection experiments, especially for dark matter models in which the scattering is sensitive to the high velocity tail of the distribution, such as inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for experiments that require high energy recoil events, such as many directionally sensitive experiments. Here we determine the velocity distribution functions from two of the highest resolution numerical simulations of Galactic dark matter structure (Via Lactea II and GHALO), and study the effects for these scenarios. For directional detection, we find that the observed departures from Maxwell-Boltzmann increase the contrast of the signal and change the typical direction of incoming DM particles. For iDM, the expected signals at direct detection experiments are changed dramatically: the annual modulation can be enhanced by more than a factor two, and the relative rates of DAMA compared to CDMS can change by an order of magnitude, while those compared to CRESST can change by a factor of two. The spectrum of the signal can also change dramatically, with many features arising due to substructure. For LDM the spectral effects are smaller, but changes do arise that improve the compatibility with existing experiments. We find that the phase of the modulation can depend upon energy, which would help discriminate against background should it be found.Comment: 34 pages, 16 figures, submitted to JCAP. Tables of g(v_min), the integral of f(v)/v from v_min to infinity, derived from our simulations, are available for download at http://astro.berkeley.edu/~mqk/dmdd

Studies of a three-stage dark matter and neutrino observatory based on multi-ton combinations of liquid xenon and liquid argon detectors

We study a three stage dark matter and neutrino observatory based on multi-ton two-phase liquid Xe and Ar detectors with sufficiently low backgrounds to be sensitive to WIMP dark matter interaction cross sections down to 10E-47 cm^2, and to provide both identification and two independent measurements of the WIMP mass through the use of the two target elements in a 5:1 mass ratio, giving an expected similarity of event numbers. The same detection systems will also allow measurement of the pp solar neutrino spectrum, the neutrino flux and temperature from a Galactic supernova, and neutrinoless double beta decay of 136Xe to the lifetime level of 10E27 - 10E28 y corresponding to the Majorana mass predicted from current neutrino oscillation data. The proposed scheme would be operated in three stages G2, G3, G4, beginning with fiducial masses 1-ton Xe + 5-ton Ar (G2), progressing to 10-ton Xe + 50-ton Ar (G3) then, dependent on results and performance of the latter, expandable to 100-ton Xe + 500-ton Ar (G4). This method of scale-up offers the advantage of utilizing the Ar vessel and ancillary systems of one stage for the Xe detector of the succeeding stage, requiring only one new detector vessel at each stage. Simulations show the feasibility of reducing or rejecting all external and internal background levels to a level <1 events per year for each succeeding mass level, by utilizing an increasing outer thickness of target material as self-shielding. The system would, with increasing mass scale, become increasingly sensitive to annual signal modulation, the agreement of Xe and Ar results confirming the Galactic origin of the signal. Dark matter sensitivities for spin-dependent and inelastic interactions are also included, and we conclude with a discussion of possible further gains from the use of Xe/Ar mixtures

The generalised NMSSM at one loop: fine tuning and phenomenology

We determine the degree of fine tuning needed in a generalised version of the NMSSM that follows from an underlying Z4 or Z8 R symmetry. We find that it is significantly less than is found in the MSSM or NMSSM and extends the range of Higgs mass that have acceptable fine tuning up to Higgs masses of mh ~ 130 GeV. For universal boundary conditions analogous to the CMSSM the phenomenology is rather MSSM like with the singlet states typically rather heavy. For more general boundary conditions the singlet states can be light, leading to interesting signatures at the LHC and direct detection experiments.Comment: 20 pages, 9 figures, matches published versio

Interplay between Fermi gamma-ray lines and collider searches

We explore the interplay between lines in the gamma-ray spectrum and LHC searches involving missing energy and photons. As an example, we consider a singlet Dirac fermion dark matter with the mediator for Fermi gamma-ray line at 130 GeV. A new chiral or local U(1) symmetry makes weak-scale dark matter natural and provides the axion or Z 0 gauge boson as the mediator connecting between dark matter and electroweak gauge bosons. In these models, the mediator particle can be produced in association with a monophoton at colliders and it produces large missing energy through the decays into a DM pair or ZZ; Z with at least one Z decaying into a neutrino pair. We adopt the monophoton searches with large missing energy at the LHC and impose the bounds on the coupling and mass of the mediator field in the models. We show that the parameter space of the Z 0 mediation model is already strongly constrained by the LHC 8TeV data, whereas a certain region of the parameter space away from the resonance in axion-like mediator models are bounded. We foresee the monophoton bounds on the Z 0 and axion mediation models at the LHC 14 TeV