We analyze the unique capability of the existing SeaQuest experiment at Fermilab to discover wellmotivated dark sector physics by measuring displaced electron, photon, and hadron decay signals behind a compact shield. A planned installation of a refurbished electromagnetic calorimeter could provide powerful new sensitivity to GeV-scale vectors, dark Higgs bosons, scalars, axions, and inelastic and strongly interacting dark matter models. This sensitivity is both comparable and complementary to NA62, SHiP, and FASER. SeaQuest's ability to collect data now and over the next few years provides an especially exciting opportunity.

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). The prospects for detection in near future dark matter experiments and/or the upcoming 14 TeV LHC appear quite promising.

No abstract

The proposed LDMX experiment would provide roughly a meter-long region of instrumented tracking and calorimetry that acts as a beam stop for multi-GeV electrons in which each electron is tagged and its evolution measured. This would offer an unprecedented opportunity to access both collider-invisible and ultra-short lifetime decays of new particles produced in electron (or muon)-nuclear fixed-target collisions. In this paper, we show that the missing momentum channel and displaced decay signals in such an experiment could provide world-leading sensitivity to sub-GeV dark matter, millicharged particles, and visibly or invisibly decaying axions, scalars, dark photons, and a range of other new physics scenarios.

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. Upon decaying, these particles can significantly reheat the visible sector, diluting the abundance of dark matter and thus allowing for dark matter particles that are much heavier than conventional WIMPs. In this paper, we present a systematic and pedagogical treatment of the cosmological history in this class of models, emphasizing the simplest scenarios in which a dark matter candidate annihilates into hidden sector particles which then decay into visible matter through the vector, Higgs, or lepton portals. In each case, we find ample parameter space in which very heavy dark matter particles can provide an acceptable thermal relic abundance. We also discuss possible extensions of models featuring these dynamics.

The EDGES Collaboration has recently reported the detection of a stronger-than-expected absorption feature in the global 21-cm spectrum, centered at a frequency corresponding to a redshift of z ≃ 17. This observation has been interpreted as evidence that the gas was cooled during this era as a result of scattering with dark matter. In this Letter, we explore this possibility, applying constraints from the cosmic microwave background, light element abundances, Supernova 1987A, and a variety of laboratory experiments. After taking these constraints into account, we find that the vast majority of the parameter space capable of generating the observed 21-cm signal is ruled out. The only viable models are those in which a small fraction, ∼0.3%-2%, of the dark matter consists of particles with a mass of ∼10-80 MeV and which couple to the photon through a small electric charge, roughly 10 −6 -10 −4 as large as the electron charge. Furthermore, in order to avoid being overproduced in the early Universe, such models must be supplemented with an additional depletion mechanism, such as annihilations through a L μ -L τ gauge boson or annihilations to a pair of rapidly decaying hidden sector scalars.

In recent years, direct detection, indirect detection, and collider experiments

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. For concreteness, we consider a simple realization with a Dirac fermion dark matter candidate coupled to a massive gauge boson that decays to the Standard Model through its kinetic mixing with hypercharge. We identify viable parameter space in which the dark matter can be as heavy as ∼1-100 PeV without being overproduced in the early universe.The Weakly Interacting Massive Particle (WIMP) paradigm provides a compelling cosmological origin for dark matter (DM) candidates with weak-scale masses and interactions. In the early universe, at temperatures above the WIMP's mass, interactions with the Standard Model (SM) produce a thermal population of WIMPs and sustain chemical equilibrium between dark and visible matter. When the temperature falls below the WIMP's mass, these interactions freeze-out to yield an abundance similar to the observed cosmological DM density. This narrative is known as the "WIMP miracle."In recent years, however, this framework has become increasingly constrained. The Large Hadron Collider has not yet discovered any new physics, and limits from direct detection experiments have improved at an exponential rate over the past decade. For DM candidates that annihilate at a sufficient rate to avoid being overproduced in the early universe, unacceptably large elastic scattering cross sections with nuclei are often predicted. To evade these constraints, one is forced to consider models that include features such as coannihilations [1,2], resonant annihilations [1,3], pseudoscalar couplings [4][5][6][7], or annihilations to final states consisting of leptons or electroweak bosons [8][9][10][11][12][13][14][15][16].It is equally plausible, however, that the DM is a singlet under the SM and was produced independently of the visible sector during the period of reheating that followed inflation (for a review, see Ref.[17]). By freezingout through annihilations to SM singlets, the DM in such models can avoid being overproduced while easily evading the constraints from direct detection experiments [18][19][20][21][22][23][24][25]. In this letter, we explore this class of scenarios, focusing on hidden sectors that are thermally decoupled and, therefore, never reach equilibrium with the visible sector. In this case, the DM freezes-out of chemical equilibrium within its own sector, unaffected by SM dynamics.So long as the hidden sector consists entirely of SM singlets, renormalizable interactions between the SM and the DM can proceed only through the following gauge singlet operators: H † H, ...