Properties Of Dark Matter Particles Under Gravitation

Although many astronomical and cosmological observations have confirmed the dark matter,its particle properties are still unknown.On the one hand,the reason for the super long lifetime of dark matter particles is not completely clear;on the other hand,whether dark matter particles annihilate,what the final state particles are is not clear.Based on the fact that most of the evidence for the existence of dark matter comes from its gravitational interaction,this paper studies the phenomenology of dark matter decay or annihilation through nonminimal coupling to gravity.Global symmetry can guarantee the stability of dark matter particles.However,the nonminimal coupling between dark matter and gravity can destroy global symmetry,leading to dark matter decay.Under the framework of nonminimal coupling between scalar singlet dark matter and gravity,it is worth exploring to what extent the global symmetry is broken.It is suggested that the total amount of decay products of scalar singlet dark matter cannot exceed current observational constraints.Along these lines,the data obtained with satellites such as Fermi-LAT and AMS-02 can limit the global symmetry breaking strength.Since the mass of many well-motivated dark matter candidates may be in the GeV-TeV range,we determine a reasonable parameter range for the lifetime in this range.We find that when the mass of the scalar singlet dark matter is around the electroweak scale(246 GeV),the corresponding 3σ lower limits of the lifetime of scalar singlet dark matter is 5.3 × 1026 s.Our analysis of scalar singlet dark matter around the typical electroweak scale contains the most abundant decay channels of all mass ranges,so the study of the behavior of scalar singlet dark matter under the influence of gravity is comprehensive.Considering that nonminimal coupling between the Higgs field and gravity can also exist,we should consider its effects on the physical process that dark matter decays from gravity portals.It turns out that the existence of nonminimal coupling between the Higgs field and gravity can provide additional decay width when dark matter decays from the gravity portal.This extra decay width would significantly suppress standard decay width.When the dark matter is the scalar singlet,kinetic mixing between scalar singlet and the Higgs field would appear after electroweak symmetry breaking,which turns out to provide diverse decay channels that dominate the decay width.When the dark matter is fermionic singlet,its decay phenomenology is quite different from the scalar case.There would be no kinetic mixing between fermionic singlet and the Higgs field,so its decay products are very monotonous,mainly neutrinos and the Higgs bosons.For both cases,we calculated the decay rates.Then,rough limits on coupling constants are obtained from observations.The results show that the decay rates can be significantly enhanced by the nonminimal coupling of the Higgs field with gravity.Observational limits are stringent when the nonminimal coupling of the Higgs field with gravity is stronger or when the dark matter particle’s mass is heavier.Since scalar singlet dark matter decay through the gravitational portals is strongly constrained by observation,we further explore the behavior of dark matter annihilation in the framework of nonminimal coupling between scalar singlet dark matter and gravity.Based on the fact that the excess of leptons in cosmic rays may come from dark matter particles,we assume a lepton SU(2)doublet in nature as a mediator connecting dark matter and visible leptons.We analyzed constraints on dark matter annihilation through gravity portals from the cosmic antiproton flux,dark matter relic abundance,cosmic positron flux,cosmic microwave background,and direct detection experiments.The results show that there is still a vast parameter space that is compatible with the existing experiments.We further show that the purely gravitational dark matter can better explain the lepton excess of DAMPE.The required Yukawa coupling strength between muon and the scalar mediator is about 4.5 times that of the electron and the scalar mediator.Our work provides a promising mechanism for the connection between dark matter particles and standard model particles.