Alternative Approaches to Dark Matter Puzzle

Abstract

We study the dark matter problem with particular reference to a candidate particle within the Standard Model: the $H$ dibaryon. We consider as well a scenario which aims to connect the dark matter origin to the Baryon Asymmetry of the Universe, studying the examples of $H$ and of a BSM particle $X$. Strongly attractive color forces in the flavor singlet channel may lead to a tightly bound and compact $H$ dibaryon. We find that the observation of $\Lambda$ decays from doubly-strange hypernuclei puts a constraint on the $H$ wavefunction which is plausibly satisfied. In this case the $H$ is long-lived as we calculate. We also show that an $H$ or another compact, flavor singlet hadron is unlikely to bind to nuclei, so that experimental bounds on exotic isotopes do not exclude their existence. Remarkably, the $H$ appears to evade other experimental constraints as well, when account is taken of its expected compact spatial wavefunction. We check whether the $H$ is a viable DM candidate by considering DM experiments sensitive to light particles. Taking into account the DM interaction in the crust above underground detectors we find a window in the exclusion limits in the micro-barn, $m\lsi 2.4$ GeV, range which coincides with the range expected for the tightly bound $H$. Finally, we present a scenario in which DM carries (anti-)baryon number and which offers a mechanism to generate the baryon asymmetry observed in the Universe. If $\sigma^{annih} _{\bar{X}} < \sigma^{annih}_{X}$, the $\bar{X}$'s freeze out at a higher temperature and have a larger relic density than $X$'s. If $m_X \lsi 4.5 B_X$ GeV and the annihilation cross sections differ by 10% or more, this type of scenario naturally explains the observed $\Omega_{DM} \simeq 5 \Omega_b$. Two examples are given, the $H$ and an hypothetical BSM candidate $X$.