20 research outputs found
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
Galactic Globular Clusters as a test for Very Low-Mass stellar models
We make use of the Next Generation model atmospheres by Allard et al. (1997)
and Hauschildt, Allard & Baron (1999) to compute theoretical models for low and
very low-mass stars for selected metallicities in the range Z= 0.0002 to 0.002.
On this basis, we present theoretical predictions covering the sequence of
H-burning stars as observed in galactic globulars from the faint end of the
Main Sequence up to, and beyond, the cluster Turn Off. The role played by the
new model atmospheres is discussed, showing that present models appear in
excellent agreement with models by Baraffe et al. (1997) as computed on quite
similar physical basis. One finds that the theoretical mass-luminosity
relations based on this updated set of models, are in good agreement with the
empirical data provided by Henry & McCarthy (1993). Comparison with HST
observation discloses that the location in the Color-Magnitude diagram of the
lower Main Sequence in galactic globular clusters appears again in good
agreement with the predicted sensitive dependence of these sequences on the
cluster metallicity.Comment: accepted for pubblication on MNRA
Astrophysical tests of mirror dark matter
Mirror matter is a self-collisional dark matter candidate. If exact mirror
parity is a conserved symmetry of the 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 only via gravity, therefore mirror matter is naturally "dark". The most
promising way to test this dark matter candidate is to look at its
astrophysical signatures, as Big Bang nucleosynthesis, primordial structure
formation and evolution, cosmic microwave background and large scale structure
power spectra.Comment: 9 pages, 2 figure
Cosmology with Mirror Dark Matter
Mirror matter is a stable self-collisional dark matter candidate. If parity
is a conserved unbroken symmetry of nature, there could exist a parallel hidden
(mirror) sector of the Universe composed of particles with the same masses and
obeying the same physical laws as our (visible) sector, except for the opposite
handedness of weak interactions. The two sectors interact predominantly via
gravity, therefore mirror matter is naturally "dark". Here I review the
cosmological signatures of mirror dark matter, concerning thermodynamics of the
early Universe, Big Bang nucleosynthesis, primordial structure formation and
evolution, cosmic microwave background and large scale structure power spectra.
Besides gravity, the effects on primordial nucleosynthesis of the kinetic
mixing between photons and mirror photons are considered. 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: 80 pages, 31 figures; invited review for Int.J.Mod.Phys.
Mirror World, Supersymmetric Axion and Gamma Ray Bursts
A modification of the relation between axion mass and the PQ constant permits
a relaxation of the astrophysical constraints, considerably enlarging the
allowed axion parameter space. We develop this idea in this paper, discussing a
model for an {\it ultramassive} axion, which essentially represents a
supersymmetric Weinberg-Wilczek axion of the mirror world. The experimental and
astrophysical limits allow a PQ scale f_a ~ 10^4-10^6 GeV and a mass m_a ~
1MeV, which can be accessible for future experiments.
On a phenomenological ground, such an {\it ultramassive} axion turns out to
be quite interesting. It can be produced during the gravitational collapse or
during the merging of two compact objects, and its subsequent decay into e+e-
provides an efficient mechanism for the transfer of the gravitational energy of
the collapsing system to the electron-positron plasma. This could resolve the
energy budget problem in the Gamma Ray Bursts and also help in understanding
the SN type II explosion phenomena.Comment: 20 pages, 5 eps figures, added footnote and reference
Notes on Hidden Mirror World
A few remarks on Dark Matter (DM) models are presented. An example is Mirror
Matter which is the oldest but still viable DM candidate, perhaps not in the
purest form. It can serve as a test-bench for other analogous DM models, since
the properties of macroscopic objects are quite firmly fixed for Mirror Matter.
A pedagogical derivation of virial theorem is given and it is pointed out that
concepts of virial velocity or virial temperature are misleading for some
cases. It is shown that the limits on self-interaction cross-sections derived
from observations of colliding clusters of galaxies are not real limits for
individual particles if they form macroscopic bodies. The effect of the heating
of interstellar medium by Mirror Matter compact stars is very weak but may be
observable. The effect of neutron star heating by accretion of M-baryons may be
negligible. Problems of MACHOs as Mirror Matter stars are touched upon.Comment: Latex, revtex, 24 pages, 1 figure, references updated and adde
More about neutron - mirror neutron oscillation
It was pointed out recently that oscillation of the neutron into mirror
neutron , a sterile twin of the neutron with exactly the same mass, could
be a very fast process with the the baryon number violation, even faster than
the neutron decay itself. This process is sensitive to the magnetic fields and
it could be observed by comparing the neutron lose rates in the UCN storage
chambers for different magnetic backgrounds. We calculate the probability of
oscillation in the case when a mirror magnetic field is
non-zero and show that in this case it can be suppressed or resonantly enhanced
by applying the ordinary magnetic field , depending on its strength
and on its orientation with respect to . The recent experimental
data, under this hypothesis, still allow the oscillation time order 1 s
or even smaller. Moreover, they indicate that the neutron losses are sensitive
to the orientation of the magnetic field. %at about level. If these
hints will be confirmed in the future experiments, this would point to the
presence of the mirror magnetic field on the Earth of the order of 0.1 G, or
some equivalent spin-dependent force of the other origin that makes a
difference between the neutron and mirror neutron states.Comment: 10 page