Neutralino-neutralino Annihilation Research Articles

Neutralino-neutralino annihilation toγZin MSSM

The 1-loop computation of the processes $\tchi_i \tchi_j \to \gamma Z$ has been performed at an arbitrary c.m. energy for any pair of MSSM neutralinos. As an application suitable for Dark Matter (DM) searches, the neutralino-neutralino annihilation is studied at the limiting case of vanishing relative velocity, describing the present DM distribution in the galactic halo; and at a relative velocity of about 0.5, determining the neutralino relic density contributions. The most useful situation is obviously for $i=j=1$, but the case of non-identical neutralinos may also be useful in some corners of the parameter space. Our results are contained in the FORTRAN code PLATONdmgZ, applying to any set of real MSSM parameters. Numerical results are also presented for a sample of 6 MSSM models, describing the various possible neutralino properties. A comparison with other existing works is also made.

Neutralino-neutralino annihilation to photon and gluon pairs in MSSM models

The complete 1-loop computation of the processes $(\tchi^0_i \tchi^0_j \leftrightarrow\gamma\gamma, ~ gg)$, for any pair of the four MSSM neutralinos, has been performed for an arbitrary c.m energy. As a first application suitable for Dark Matter (DM) searches, the neutralino-neutralino annihilation is studied at relative velocities $v/c\simeq 10^{-3}$ describing the present DM distribution in the galactic halo, and $v/c\simeq 0.5$ determining neutralino relic density contributions. Numerical results are presented for 31 MSSM benchmark models indicating considerable sensitivity to the input parameters. Numerical codes are released, which may be used for the computation of the annihilation of any two neutralinos to two photons or two gluons at the aforementioned $v/c$ values. In the near future, we intend to complement them with codes for the inverse process $\gamma\gamma \to \tchi^0_i \tchi^0_j$, observable at the future high energy Linear Colliders.

Neutralino pair production in a $\gamma \gamma $ collider

We present a complete one-loop study of the process $\gamma \gamma \to {\tilde \chi}^0_i {\tilde \chi}^0_j$ and the predicted cross section in a $\gamma \gamma $ Linear Collider. A suitable numerical code, PLATONlc, valid for any set of real MSSM parameters, is released. This study and code are complementary to those suitable for dark matter detection through the inverse process ${\tilde \chi}^0_i {\tilde \chi}^0_j \to \gamma\gamma$ describing neutralino-neutralino annihilation at rest, which were presented previously. If SUSY is realized in nature, both codes should be very helpful in future astrophysical and collider studies of the neutralino sector.

On neutralino stars as microlensing objects

The microlensing objects, Machos, recently observed in the halo of our Galaxy, can be interpreted as dense neutralino objects, neutralino stars, produced by the gravitational instability of neutralino ggas. Taking the mass and radius of these objects from microlensing observations we calculated the diffuse gamma-ray flux produced in neutralino-neutralino annihilation inside the objects. The resulting flux is many orders of magnitude higher than the observed one.

Signals from relic neutralinos

Analysis and comparison of various methods for detecting relic neutralinos are discussed, considering the most general neutralino compositions and modelling the neutralino local density according to its relic abundance. Special attention is devoted to the discussion of the antiproton flux generated by neutralino-neutralino annihilation in the galactic halo.

On the neutralino as dark matter candidate. I. Relic abundance

The neutralino relic abundance is evaluated for a wide range of the neutralino mass, 20 GeV ≤ m x ≤ 1 TeV, by taking into account the full set of final states in the neutralino-neutralino annihilation. The analysis is performed in the Minimal SuSy Standard Model; it is not restricted by stringent GUT assumptions but only constrained by present experimental bounds. We also discuss phenomenological aspects which are employed in the companion paper (Part II. Direct detection) where the chances for a successful search for dark matter neutralino are investigated.

A new investigation on neutralino dark matter: relic density and detection rates

The main properties of the neutralino dark matter are revisited in the light of the new theoretical developments in Susy theories and of the recent constraints from accelerators and underground experiments. The neutralino relic abundance and the detection rates relevant for direct and indirect searches are evaluated in the minimal supersymmetric standard model (MSSM) with the full inclusion of the (one-loop) radiative corrections, both to the Higgs masses and to the trilinear Higgs self-coupling. The relevance of these corrections for the neutralino-neutralino annihilation cross-section, and thus for the relic density, is discussed in detail. Large regions of the parameter space are considered, including those where the neutralino only provides a fraction of the local dark matter density; in these domains the standard value for the local density is appropriately scaled down. Some general properties of the detection rates as functions of the MSSM parameters are also elucidated; in particular it is shown that in the regions of the parameter space where scaling of the local density occurs, the rates are largely independent of two of the model free parameters. The relevance of the Kamiokande upper bounds to the upgoing muon fluxes is discussed in connection with the possible neutrino outputs from the Earth and from the Sun due to neutralino accumulation and annihilation in these macroscopic bodies. Finally, the complementarity between the search for neutralino dark matter and the discovery potential of future accelerators is discussed.

Is it possible to detect the gamma-ray line from neutralino-neutralino annihilation?

We present the calculations of the gamma-ray flux produced by neutralino annihilation (χ+χ→γ+γ) in our Galaxy. Most attention is paid to the case in which the dark matter in and outside our Galaxy consists of neutralinos. It is shown that in this case the flux is essentially determined by only two physical quantities: the critical density ϱ c =1.1×10 -29g/cm 3 and the local (solar neighbourhood) density of dark matter ϱ ⊙≅0.3 GeV/cm 3. Detectors of large area ( S⩾10 5 cm 2) and very high energy resolution ( ΔE E ∼10 -4−10 -5 ) are needed for the detection of the predicted flux ( I γ ≲1×10 -12cm -12s -1sr -1). A (marginally) detectable gamma-ray flux is found only for an extreme combination of assumptions: the neutralino is almost a pure photino, the lightest sfermion is a slepton with mass ∼50 GeV, and the average density of neutralinos in the Universe is ω χ = 0.03.

Indirect search for neutralinos at neutrino telescopes

Under the assumption that cold dark matter is composed (at least partially) of neutralinos, capture and pair annihilation of these particles in the sun and the earth are evaluated in the framework of the minimal SUSY extension of the standard model (MSSM), taking into account the effects due to the radiative corrections to the masses of the Higgs bosons. The flux of the neutrinos produced in the neutralino-neutralino annihilation and the relevant rate of the muons generated by neutrino conversion in the earth and crossing a detector upwardly are calculated. The present experimental limits from underground detectors are employed to set constraints on the MSSM parameters, and the capabilities of future neutrino telescopes to further explore regions in parameter space are analyzed.

Rate for annihilation of galactic dark matter into two photons.

We perform a calculation of the cross section for neutralino-neutralino annihilation into two photons and apply it to dark matter in the galactic halo to find the counting rate in a large \ensuremath{\gamma}-ray detector such as EGRET or ASTROGAM. Combining constraints from particle accelerators with the requirement that the neutralinos make up the dark matter we find that rates over a few dozen events per year are unlikely. We list the assumptions that go into our conclusions and suggest other particle dark-matter candidates which could give larger and perhaps observable signals.