Dark matter candidates arise naturally in many models that address the hierarchy problem. In the fraternal twin Higgs model which could explain the absence of the new physics signals at the Large Hadron Collider (LHC), there are several viable dark matter candidates. In this paper we study the twin neutrino in the mass range ∼ 0.1-10 GeV as the dark matter. The thermal relic density is determined by the interplay of several annihilation and scattering processes between the twin neutrino, twin tau, and twin photon, depending on the order of the freeze-out temperatures of these processes. Besides the common coannihilation scenario where the relic density is controlled by the twin tau annihilation, it can realize the recently discovered coscattering phase if the scattering of the twin neutrino into the twin tau freezes out earlier than the twin tau annihilation. We also provide a method to calculate the thermal relic density in the intermediate regime where both coannihilation and coscattering processes contribute to the determination of the dark matter density. We show that the right amount of dark matter can be obtained in various scenarios in different regions of the parameter space. The current experimental constraints and future probes into the parameter space from direct detections, cosmological and astrophysical bounds, dark photon searches, and displaced decays at colliders, are discussed.

Using a simplified framework, we attempt to explain the recent DAMPE cosmic e + + e − flux excess by leptophilic Dirac fermion dark matter (LDM). The scalar (Φ 0 ) and vector (Φ 1 ) mediator fields connecting LDM and Standard Model particles are discussed. We find that the couplings P ⊗ S, P ⊗ P , V ⊗ A and V ⊗ V can produce the right bump in e + + e − flux for a DM mass around 1.5 TeV with a natural thermal annihilation crosssection < σv >∼ 3×10 −26 cm 3 /s today. Among them, V ⊗V coupling is tightly constrained by PandaX-II data (although LDM-nucleus scattering appears at one-loop level) and the surviving samples appear in the resonant region, m Φ 1 2m χ . We also study the related collider signatures, such as dilepton production pp → Φ 1 → + − , and muon g −2 anomaly. Finally, we present a possible U(1) X realization for such leptophilic dark matter.

It is well known that primordial black hole (PBH) can be generated in inflation process of the early universe, especially when the inflaton field has some non-trivial features that could break the slow-roll condition. In this paper, we investigate a toy model of inflation with bumpy potential, which has one or several bumps. We found that potential with multi-bump can give rise to power spectra with multi peaks in small-scale region, which can in turn predict the generation of primordial black holes in various mass ranges. We also consider the two possibilities of PBH formation by spherical collapse and elliptical collapse. And discusses the scalar-induced gravitational waves (SIGWs) generated by the second-order scalar perturbations.

We explore the LHC reach on beyond-the-Standard Model (BSM) particles X associated with a new strong force in a hidden sector. We focus on the motivated scenario where the SM and hidden sectors are connected by fermionic mediators ψ +,0 that carry SM electroweak charges. The most promising signal is the Drell-Yan production of a ψ ±ψ0 pair, which forms an electrically charged vector bound state Υ ± due to the hidden force and later undergoes resonant annihilation into W ± X. We analyze this final state in detail in the cases where X is a real scalar φ that decays to bb, or a dark photon γ d that decays to dileptons. For prompt X decays, we show that the corresponding signatures can be efficiently probed by extending the existing ATLAS and CMS diboson searches to include heavy resonance decays into BSM particles. For long-lived X, we propose new searches where the requirement of a prompt hard lepton originating from the W boson ensures triggering and essentially removes any SM backgrounds. To illustrate the potential of our results, we interpret them within two explicit models that contain strong hidden forces and electroweak-charged mediators, namely λ-supersymmetry (SUSY) and non-SUSY ultraviolet extensions of the Twin Higgs model. The resonant nature of the signals allows for the reconstruction of the mass of both Υ ± and X, thus providing a wealth of information about the hidden sector. *

We study the recent e ± cosmic ray excess reported by DAMPE in a Hidden Valley Model with lepton-portal dark matter. We find the electron-portal can account for the excess well and satisfy the DM relic density and direct detection bounds, while electron+muon/electron+muon+tauportal suffers from strong constraints from lepton flavor violating observables, such as µ → 3e.We also discuss possible collider signatures of our model, both at the LHC and a future 100 TeV hadron collider.