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تسجيل مستخدم جديدStrongly Coupled Dark Energy Cosmologies: preserving LCDM success and easing low scale problems I - Linear theory revisited
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تأليف
Silvio A. Bonometto
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In this first paper we discuss the linear theory and the background evolution of a new class of models we dub SCDEW: Strongly Coupled DE, plus WDM. In these models, WDM dominates todays matter density; like baryons, WDM is uncoupled. Dark Energy is a scalar field $Phi$; its coupling to ancillary CDM, whose todays density is $ll 1, %$, is an essential model feature. Such coupling, in fact, allows the formation of cosmic structures, in spite of very low WDM particle masses ($sim 100$ eV). SCDEW models yields Cosmic Microwave Background and linear Large Scale features substantially undistinguishable from $Lambda$CDM, but thanks to the very low WDM masses they strongly alleviate $Lambda$CDM issues on small scales, as confirmed via numerical simulations in the II associated paper. Moreover SCDEW cosmologies significantly ease the coincidence and fine tuning problems of $Lambda$CDM and, by using a field theory approach, we also outline possible links with inflationary models. We also discuss a possible fading of the coupling at low redshifts which prevents non linearities on the CDM component to cause computational problems. The (possible) low-$z$ coupling suppression, its mechanism, and its consequences are however still open questions -not necessarily problems- for SCDEW models. The coupling intensity and the WDM particle mass, although being extra parameters in respect to $Lambda$CDM, are found to be substantially constrained a priori so that, if SCDEW is the underlying cosmology, we expect most data to fit also $Lambda$CDM predictions.
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Cosmologies including strongly Coupled (SC) Dark Energy (DE) and Warm dark matter (SCDEW) are based on a conformally invariant (CI) attractor solution modifying the early radiative expansion. Then, aside of radiation, a kinetic field $Phi$ and a DM c
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asier at a specific time, i.e., when the asymptotic mass $m_H$, acquired by the $psi$ field at the higgs scale, becomes dominant, so that the typical BH mass $M_{BH}$ depends on $m_H$ value. For instance, if $m_H sim 100,$ eV $(1$ keV$)$ and the coupling $beta sim 8.35 (37)$, PBH with $M_{BH} simeq 10^7-10^8 $ $(10^3-10^4), M_odot$ could form. The very mechanism enhancing PBH formation also causes technical difficulties to evaluate the transfer function of SCDEW models at high $k$. A tentative solution of this problem leaves only minor discrepancies from $Lambda$CDM, also at these scales, gradually vanishing for greater $m_H$ values. We conclude that, for suitable parameter choices, SCDEW models could be the real physics underlying $Lambda$ CDM, so overcoming its fine tuning and coincidence problems, with the extra bonus of yielding large BH seeds.
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