Asher Berlin

Asher Berlin
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Asher Berlin

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Pub Categories

High Energy Physics - Phenomenology (19)
Cosmology and Nongalactic Astrophysics (12)
High Energy Astrophysical Phenomena (5)
High Energy Physics - Experiment (4)
Astrophysics of Galaxies (2)

Publications Authored By Asher Berlin

We propose a new thermal freeze-out mechanism for ultra-heavy dark matter. Dark matter coannihilates with a lighter unstable species, leading to an annihilation rate that is exponentially enhanced relative to standard WIMPs. This scenario destabilizes any potential dark matter candidate. Read More

Sterile neutrinos can be generated in the early universe through oscillations with active neutrinos and represent a popular and well-studied candidate for our universe's dark matter. Stringent constraints from X-ray and gamma-ray line searches, however, have excluded the simplest of such models. In this letter, we propose a novel alternative to the standard scenario in which the mixing angle between the sterile and active neutrinos is a dynamical quantity, induced through interactions with a light axion-like field. Read More

In recent years, direct detection, indirect detection, and collider experiments have placed increasingly stringent constraints on particle dark matter, exploring much of the parameter space associated with the WIMP paradigm. In this paper, we focus on the subset of WIMP models in which the dark matter annihilates in the early universe through couplings to either the Standard Model $Z$ or the Standard Model Higgs boson. Considering fermionic, scalar, and vector dark matter candidates within a model-independent context, we find that the overwhelming majority of these dark matter candidates are already ruled out by existing experiments. Read More

It has recently been shown that if the dark matter is in thermal equilibrium with a sector that is highly decoupled from the Standard Model, it can freeze-out with an acceptable relic abundance, even if the dark matter is as heavy as ~1-100 PeV. In such scenarios, both the dark and visible sectors are populated after inflation, but with independent temperatures. The lightest particle in the dark sector will be generically long-lived, and can come to dominate the energy density of the universe. Read More

We consider a class of models involving interactions between ultra-light scalar dark matter and Standard Model neutrinos. Such couplings modify the neutrino mass splittings and mixing angles to include additional components that vary in time periodically with a frequency and amplitude set by the mass and energy density of the dark matter. Null results from recent searches for anomalous periodicities in the solar neutrino flux strongly constrain the dark matter-neutrino coupling to be orders of magnitude below current and projected limits derived from observations of the cosmic microwave background. Read More

Motivated by the recently reported diboson and dijet excesses in Run 1 data at ATLAS and CMS, we explore models of mixed dark matter in left-right symmetric theories. In this study, we calculate the relic abundance and the elastic scattering cross section with nuclei for a number of dark matter candidates that appear within the fermionic multiplets of left-right symmetric models. In contrast to the case of pure multiplets, WIMP-nucleon scattering proceeds at tree-level, and hence the projected reach of future direct detection experiments such as LUX-ZEPLIN and XENON1T will cover large regions of parameter space for TeV-scale thermal dark matter. Read More

In this letter, we consider a class of scenarios in which the dark matter is part of a heavy hidden sector that is thermally decoupled from the Standard Model in the early universe. The dark matter freezes-out by annihilating to a lighter, metastable state, whose subsequent abundance can naturally come to dominate the energy density of the universe. When this state decays, it reheats the visible sector and dilutes all relic abundances, thereby allowing the dark matter to be orders of magnitude heavier than the weak scale. Read More

We explore the possibility that the recently reported diphoton excess at ATLAS and CMS can be accommodated within a minimal extension of a left-right symmetric model. Our setup is able to simultaneously explain the Run 2 diphoton and Run 1 diboson excesses, while providing a standard thermal freeze-out of weak-scale dark matter. In this scenario, the 750 GeV neutral right-handed Higgs triplet is responsible for the diphoton excess. Read More

We apply effective field theory methods to compute bino-nucleon scattering, in the case where tree-level interactions are suppressed and the leading contribution is at loop order via heavy flavor squarks or sleptons. We find that leading log corrections to fixed-order calculations can increase the bino mass reach of direct detection experiments by a factor of two in some models. These effects are particularly large for the bino-sbottom coannihilation region, where bino dark matter as heavy as 5-10 TeV may be detected by near future experiments. Read More

We consider a complete list of simplified models in which Majorana dark matter particles annihilate at tree level to $hh$ or $hZ$ final states, and calculate the loop-induced elastic scattering cross section with nuclei in each case. Expressions for these annihilation and elastic scattering cross sections are provided, and can be easily applied to a variety of UV complete models. We identify several phenomenologically viable scenarios, including dark matter that annihilates through the $s$-channel exchange of a spin-zero mediator or through the $t$-channel exchange of a fermion. Read More

We study a number of $U(1)_X$ models featuring a Dirac fermion dark matter particle. We perform a comprehensive analysis which includes the study of corrections to the muon magnetic moment, dilepton searches with LHC data, as well as direct and indirect dark matter detection constraints. We consider four different coupling structures, namely $U(1)_{B-L}, U(1)_{d-u}, U(1)_{universal}$, and $U(1)_{10+\bar{5}}$, all motivated by compelling extensions to the standard model. Read More

A fermion dark matter candidate with a relic abundance set by annihilation through a pseudoscalar can evade constraints from direct detection experiments. We present simplified models that realize this fact by coupling a fermion dark sector to a two-Higgs doublet model. These models are generalizations of mixed bino-Higgsino dark matter in the MSSM, with more freedom in the couplings and scalar spectra. Read More

Discovering dark matter at high energy colliders continues to be a compelling and well-motivated possibility. Weakly interacting massive particles are a particularly interesting class in which the dark matter particles interact with the standard model weak gauge bosons. Neutralinos are a prototypical example that arise in supersymmetric models. Read More

Z' gauge bosons arise in many particle physics models as mediators between the dark and visible sectors. We exploit dark matter complementarity and derive stringent and robust collider, direct and indirect constraints, as well as limits from the muon magnetic moment. We rule out almost the entire region of the parameter space that yields the right dark matter thermal relic abundance, using a generic parametrization of the Z'-fermion couplings normalized to the Standard Model Z-fermion couplings for dark matter masses in the 8 GeV-5 TeV range. Read More

Models in which dark matter particles can scatter into a slightly heavier state which promptly decays to the lighter state and a photon (known as eXciting Dark Matter, or XDM) have been shown to be capable of generating the 3.55 keV line observed from galaxy clusters, while suppressing the flux of such a line from smaller halos, including dwarf galaxies. In most of the XDM models discussed in the literature, this up-scattering is mediated by a new light particle, and dark matter annihilations proceed into pairs of this same light state. Read More

The gamma-ray excess observed from the Galactic Center can be interpreted as dark matter particles annihilating into Standard Model fermions with a cross section near that expected for a thermal relic. Although many particle physics models have been shown to be able to account for this signal, the fact that this particle has not yet been observed in direct detection experiments somewhat restricts the nature of its interactions. One way to suppress the dark matter's elastic scattering cross section with nuclei is to consider models in which the dark matter is part of a hidden sector. Read More

Motivated by the gamma-ray excess observed from the region surrounding the Galactic Center, we explore particle dark matter models that could potentially account for the spectrum and normalization of this signal. Taking a model-independent approach, we consider an exhaustive list of tree-level diagrams for dark matter annihilation, and determine which could account for the observed gamma-ray emission while simultaneously predicting a thermal relic abundance equal to the measured cosmological dark matter density. We identify a wide variety of models that can meet these criteria without conflicting with existing constraints from direct detection experiments or the Large Hadron Collider (LHC). Read More

Motivated by the recent discovery of the Higgs boson, we investigate the possibility that a missing energy plus Higgs final state is the dominant signal channel for dark matter at the LHC. We consider examples of higher-dimension operators where a Higgs and dark matter pair are produced through an off-shell Z or photon, finding potential sensitivity at the LHC to cutoff scales of around a few hundred GeV. We generalize this production mechanism to a simplified model by introducing a Z' as well as a second Higgs doublet, where the pseudoscalar couples to dark matter. Read More

The dark matter halo of the Milky Way is predicted to contain a very large number of smaller subhalos. As a result of the dark matter annihilations taking place within such objects, the most nearby and massive subhalos could appear as point-like or spatially extended gamma-ray sources, without observable counterparts at other wavelengths. In this paper, we use the results of the Aquarius simulation to predict the distribution of nearby subhalos, and compare this to the characteristics of the unidentified gamma-ray sources observed by the Fermi Gamma-Ray Space Telescope. Read More