20 research outputs found
Early Universe cosmology with mirror dark matter
Mirror matter is a stable self-collisional dark matter candidate. If exact
mirror parity is a conserved symmetry of nature, there could exist a parallel
hidden (mirror) sector of the Universe which has the same kind of particles and
the same physical laws of our (visible) sector. The two sectors interact each
other predominantly via gravity, therefore mirror matter is naturally "dark".
Here I briefly review the cosmological signatures of mirror dark matter, as Big
Bang nucleosynthesis, primordial structure formation and evolution, cosmic
microwave background and large scale structure power spectra, together with its
compatibility with the interpretation of the DAMA annual modulation signal in
terms of photon--mirror-photon kinetic mixing. Summarizing the present status
of research and comparing theoretical results with observations/experiments, it
emerges that mirror matter is not just a viable, but a promising dark matter
candidate.Comment: 10 pages, 2 figures; contributed to "Invisible Universe International
Conference", Paris, June 29 - July 3 2009; to be published in AIP proceeding
Big Bang nucleosynthesis in visible and hidden-mirror sectors
One of the still viable candidates for the dark matter is the so-called
mirror matter. Its cosmological and astrophysical implications were widely
studied in many aspects, pointing out the importance to go further with
research and refine the studies. In particular, the Big Bang nucleosynthesis
provides a strong test for every dark matter candidate, since it is well
studied and involves relatively few free parameters. The necessity of accurate
studies of primordial nucleosynthesis with mirror matter has then emerged. In
order to fill this lack, I present here the results of accurate numerical
simulations of the primordial production of both ordinary nuclides and nuclides
made of mirror baryons, in presence of a hidden mirror sector with unbroken
parity symmetry and with gravitational interactions only. These elements are
the building blocks of all the structures forming in the Universe, therefore
their chemical composition is a key ingredient for astrophysics with mirror
dark matter. The production of ordinary nuclides show differences from the
standard model for a ratio of the temperatures between mirror and ordinary
sectors x = T'/T > 0.3, and they present an interesting decrease of the
abundance of 7Li. For the mirror nuclides, instead, one observes an enhanced
production of 4He, that becomes the dominant element for x < 0.5, and much
larger abundances of heavier elements.Comment: 6 pages, 3 figure
Have neutron stars a dark matter core?
Recent observational results for the masses and radii of some neutron stars
are in contrast with typical observations and theoretical predictions for
"normal" neutron stars. We propose that their unusual properties can be
interpreted as the signature of a dark matter core inside them. This
interpretation requires that the dark matter is made of some form of stable,
long-living or in general non-annihilating particles, that can accumulate in
the star. In the proposed scenario all mass-radius measurements can be
explained with one nuclear matter equation of state and a dark core of varying
relative size. This hypothesis will be challenged by forthcoming observations
and could eventually be a useful tool for the determination of dark matter.Comment: 3 pages, 1 figur
Early Universe cosmology in the light of the mirror dark matter interpretation of the DAMA/Libra signal
Mirror dark matter provides a simple framework for which to explain the
DAMA/Libra annual modulation signal consistently with the null results of the
other direct detection experiments. The simplest possibility involves ordinary
matter interacting with mirror dark matter via photon-mirror photon kinetic
mixing of strength epsilon ~ 10^(-9). We confirm that photon-mirror photon
mixing of this magnitude is consistent with constraints from ordinary Big Bang
nucleosynthesis as well as the more stringent constraints from cosmic microwave
background measurements and large scale structure considerations.Comment: 9 pages, 1 figure; updated computations for T'(T), removed
computation of Y
Primordial He' abundance implied by the mirror dark matter interpretation of the DAMA/Libra signal
We compute the primordial mirror helium He' mass fraction emerging from Big
Bang nucleosynthesis in the mirror sector of particles in the presence of
kinetic mixing between photons and mirror photons. We explore the kinetic
mixing parameter (epsilon) values relevant for cosmology and which are also
currently probed by the dark matter direct detection experiments. In
particular, we find that for epsilon \sim 10^{-9}, as suggested by the
DAMA/Libra and other experiments, a large He' mass fraction (Y_{He'} \approx
90%) is produced. Such a large value of the primordial He' mass fraction will
have important implications for the mirror dark matter interpretation of the
direct detection experiments, as well as for the study of mirror star formation
and evolution.Comment: 8 pages, 1 figur
Active Galactic Nuclei: Jets as the Source of Hadrons and Neutrinos
Active galactic nuclei are extragalactic sources, and their relativistic hot-plasma jets are believed to be the main candidates of the cosmic-ray origin, above the so-called knee region of the cosmic-ray spectrum. Relativistic shocks, either single or multiple, have been observed or been theorized to be forming within relativistic jet channels in almost all active galactic nuclei sources. The acceleration of non-thermal particles (e.g. electrons, protons) via the shock Fermi acceleration mechanism, is believed to be mainly responsible for the power-law energy distribution of the observed cosmic-rays, which in very high energies can consequently radiate high energy gamma-rays and neutrinos, through related radiation channels. Here, we will focus on the primary particle (hadronic) shock acceleration mechanism, and we will present a comparative simulation study of the properties of single and multiple relativistic shocks, which occur in AGN jets. We will show that the role of relativistic (quasi-parallel either quasi-perpendicular) shocks, is quite important since it can dramatically alter the primary CR spectral indices and acceleration eciencies. These properties being carried onto gamma-ray and neutrino radiation characteristics, makes the combination of them a quite appealing theme for relativistic plasma and shock acceleration physics, as well as observational cosmic-ray, gamma-ray and neutrino astronomy
Thermodynamics of the early Universe with mirror dark matter
Mirror matter is a promising self-collisional dark matter candidate. Here we
study the evolution of thermodynamical quantities in the early Universe for
temperatures below ~100 MeV in presence of a hidden mirror sector with unbroken
parity symmetry and with gravitational interactions only. This range of
temperatures is interesting for primordial nucleosynthesis analyses, therefore
we focus on the temporal evolution of number of degrees of freedom in both
sectors. Numerically solving the equations, we obtain the interesting
prediction that the effective number of extra-neutrino families raises for
decreasing temperatures before and after Big Bang nucleosynthesis; this could
help solving the discrepancy in this number computed at nucleosynthesis and
cosmic microwave background formation epochs.Comment: 7 pages, 4 figures, 3 tables; changed values in Table I + minor
change
Cosmology with mirror dark matter II: Cosmic Microwave Background and Large Scale Structure
This is the second paper of a series devoted to the study of the cosmological
implications of the existence of mirror dark matter. The parallel hidden mirror
world has the same microphysics as the observable one and couples the latter
only gravitationally. The primordial nucleosynthesis bounds demand that the
mirror sector should have a smaller temperature T' than the ordinary one T, and
by this reason its evolution can be substantially deviated from the standard
cosmology. In this paper we took scalar adiabatic perturbations as the input in
a flat Universe, and computed the power spectra for ordinary and mirror CMB and
LSS, changing the cosmological parameters, and always comparing with the CDM
case. We found differences in both the CMB and LSS power spectra, and we
demonstrated that the LSS spectrum is particularly sensitive to the mirror
parameters, due to the presence of both the oscillatory features of mirror
baryons and the collisional mirror Silk damping. For x<0.3 the mirror
baryon-photon decoupling happens before the matter-radiation equality, so that
CMB and LSS power spectra in linear regime are equivalent for mirror and CDM
cases. For higher x-values the LSS spectra strongly depend on the amount of
mirror baryons. Finally, qualitatively comparing with the present observational
limits on the CMB and LSS spectra, we show that for x<0.3 the entire dark
matter could be made of mirror baryons, while in the case x>0.3 the pattern of
the LSS power spectrum excludes the possibility of dark matter consisting
entirely of mirror baryons, but they could present as admixture (up to 50%) to
the conventional CDM.Comment: 36 pages, 19 figures; minor corrections in introduction, conclusions
and references; accepted for publication in IJMP