New gamma ray signal from gravitationally boosted neutralinos at the Galactic Center

Abstract

We discuss on the possibility that colliding dark matter particles in the form of neutralinos may be gravitationally boosted near the super-massive black hole at the galactic center so that they can have enough collision energy to annihilate into a stau pair. Since in some phenomenologically favored supersymmetric models the mass splitting between the neutralino and the lightest stau, one of the two scalar superpartners of the tau lepton, is a few GeVs, this channel may be allowed. In addition, staus can only decay into a tau lepton and another neutralino. We calculate the gamma-ray spectrum and flux generated by the tau pair discussing the observability of the obtained features.PACS numbers: 95.35.+d, 12.60.Jv, 98.35.Gi Dark matter (DM) accounts for more than 80% of the mass of the Universe but its nature is still one of the open problems in Physics. In a widely accepted theoretical scenario, DM is formed by a weakly interacting massive particle (WIMP) that has been in thermal equilibrium with Standard Model (SM) matter in the early Universe, leaving, after decoupling, the DM relic density as inferred by WMAP [1]. In this light, supersymmetric (SUSY) extensions of the SM provide a natural WIMP candidate. In the minimal supersymmetric standard model (MSSM), R-parity conservation assures that if the lightest supersymmetric particle is the lightest of the four neutralino states-indicated as χ in the following-, this particle is absolutely stable. In a phenomenologically favored scenario of the constrained MSSM (CMSSM), the stau coannihilation region (τ CR ) [2], the lightest stau,τ 1 , one of the scalar super-partners of the tau lepton, is close in mass to the neutralino. In theτ CR parameter space the cross section for non-relativistic annihilation into fermions of the SM, χχ → ff , is typically small and results in a too large relic density. However, including the so-called coannihilation processes [3], as for example χτ 1 ,τ 1τ1 collisions, when the mass splittings of the involved particles are small, one can efficiently enhance the thermally averaged cross section σv , and, consequently, diminish the relic density to the measured value.The standard cosmological model predict that nonrelativistic cold DM particles (v/c ∼ 10 −3 ) cluster into halos [4] that contain baryonic matter. Since DM in the halo follows a certain mass distribution, the two-body annihilation processes can happen at a rate that is proportional to the DM mass density squared. Therefore, the highest chances to detect an observable indirect signal of their existence are attained in a region with high DM density, in particular, in the galactic center (GC). Among * mirco.cannoni@dfa.uhu.es † mario.gomez@dfa.uhu.es ‡ mperezga@usal.es § vergados@uoi.gr the various signatures from DM annihilation, gamma-ray signals have received much attention. A continuum spectrum of secondary photons may arise from hadronization and decay of the annihilation products [5] and from radiation from final state charged particles [6]. Direct annihilation into photon...

Upper limits of particle emission from high-energy collision and reaction near a maximally rotating Kerr black hole

“…In this context, it should be noted that that Cannoni et al [34] discuss the possibility that colliding dark matter particles in the form of neutralinos may be gravitationally boosted near the supermassive black hole at the galactic center so that they can have enough collision energy to annihilate into a stau pair in some phenomenologically favored supersymmetric models. They also suggest the possibility that the signatures of the new channel of the reactions in gamma-ray spectrum might be discriminated by the Fermi-LAT satellite observation.…”

Ultra-high energy collisions of nonequatorial geodesic particles near dirty black holes

“…Although for the Kerr black hole [2], [3] the products of such collisions have a quite modest energy in the frame of a distant observer due to strong red shift, the observational outcome can become more significant for dirty black holes [4]. In addition, there are hopes on some indirect manifestations of this effect due to new channels of reactions with * Electronic address: zaslav@ukr.net transmutation of particles (in particular, of dark matter) near the black hole horizon [5], [6].…”

Diffusion of dark matter in a hot and dense nuclear environment

“…Usually, the incoming DM particle is supposed to be thermalized in the galaxy with the Maxwellian mean velocitiesv ∼ 220 km/s. However, in the scenario we consider, an accreting dense star (typically with the mass and dimensions of a neutron star), general relativistic effects are non-negligible and are capable of providing a sizable gravitational boost to the incoming DM particle [19,25]. Let us consider, in order to be concrete, a canonical neutron star of mass M N S ≃ 1.5M ⊙ and radius R N S ≃ 12 km.…”

“…In this way (neutral) DM particles can acquire large velocities v ∼ c and scatter very dense macroscopic regions of size nearly the radius of the star R ∼ 10 − 12 km. This extent has so far only been marginally explored [19,20]. In this work we will focus on the impact of the relativistic contribution of scalar and vector χN couplings to the spin-independent (SI) diffusion of DM inside a dense and hot nuclear medium.…”