Superheavy dark matter in $$R+R^2$$ R + R 2 cosmology w
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Regular Article - Theoretical Physics
Superheavy dark matter in R + R2 cosmology with conformal anomaly E. V. Arbuzova1,2,a , A. D. Dolgov2,3,b , R. S. Singh2,c 1
Department of Higher Mathematics, Dubna State University, Universitetskaya ul. 19, Dubna 141983, Russia Department of Physics, Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia 3 ITEP, Bol. Cheremushkinskaya 25, Moscow 117218, Russia
2
Received: 12 August 2020 / Accepted: 31 October 2020 © The Author(s) 2020
Abstract Cosmological evolution and particle creation in R 2 -modified gravity are considered for the case of the dominant decay of the scalaron into a pair of gauge bosons due to conformal anomaly. It is shown that in the process of thermalization superheavy dark matter with the coupling strength typical for the GUT SUSY can be created. Such dark matter would have the proper cosmological density if the particle mass is close to 1012 GeV.
σann v = α 2 /m 2X
1 Introduction The most popular and natural hypothesis that dark matter consists of the lightest supersymmetric particles (LSP) somewhat lost its popularity since no manifestation of supersymmetry (SUSY) was observed at LHC [1]. The LHC data significantly restricted parameter space open for SUSY. Though strictly speaking low energy SUSY, around 1 TeV, is not excluded and no direct limits from below on the LSP mass were presented, see [2], still a study of higher energy SUSY and heavier LSPs can be of interest. Different mechanisms of LSP production in cosmology are summarized in Ref. [3]. If they behave as the the usual WIMPs, then their frozen number density is governed by the Zeldovich equation [4], see also [5,6]. This equation was first derived by Zeldovich [4] and later rederived in detail in several textbook, see e.g. [7,8]. According to them the number density of thermal relics can be estimated as 1 nX , ≈ nγ m Pl m X σann v a e-mail:
where m X is the mass of would-be dark matter particles X and n X and n γ are the contemporary number densities of Xparticles and CMB photons respectively, m Pl = 1.2 · 1019 GeV is the Planck mass, and σ v is the product of the annihilation cross-section of X X¯ by their center of mass velocity. This result is valid for a simple order of magnitude estimates with some numerical and logarithmic factor of order 10 neglected. For S-wave annihilation
(1.1)
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b e-mail:
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c e-mail:
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(1.2)
In what follows we assume that α ≈ 0.01, which is typical for SUSY. If the coupling is different and/or the annihilation is enhanced or suppressed, the result would be evidently changed. Anyhow the presented expressions are the conventional ones for the estimates of usual WIMPs number and energy densities. Though there exist other mechanisms of LSP production/annihilation, which may be realized in cosmology, nevertheless a study of alternative cosmological models for LSPs as viable dark matter candidate can be of interest. Our results obtained in R
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