239 research outputs found
Primordial heavy elements in composite dark matter models
A widely accepted viewpoint is to consider candidates for cosmological dark
matter as neutral and weakly interacting particles, as well as to consider only
light elements in the pregalactic chemical composition. It is shown that stable
charged leptons and quarks can exist and, hidden in elusive atoms, play the
role of dark matter. The inevitable consequence of realistic scenarios with
such composite atom-like dark matter is existence of significant or even
dominant fraction of "atoms", binding heavy -2 charged particles and He-4
nuclei. Being alpha-particles with shielded electric charge, such atoms
catalyse a new path of nuclear transformations in the period of Big Bang
Nucleosynthesis, which result in primordial heavy elements. The arguments are
given, why such scenario escapes immediate contradiction with observations and
challenges search for heavy stable charged particles in cosmic rays and at
accelerators.Comment: Prepared for Proceedings of Blois2007 Conferenc
Probes for 4th generation constituents of dark atoms in Higgs boson studies at the LHC
The nonbaryonic dark matter of the Universe can consist of new stable charged
species, bound in heavy neutral "atoms" by ordinary Coulomb interaction. Stable
(anti-)quarks of 4th generation, bound in stable colorless () clusters, are captured by the primordial helium, produced in
Big Bang Nucleosynthesis, thus forming neutral "atoms" of O-helium (OHe), a
specific nuclear interacting dark matter that can provide solution for the
puzzles of direct dark matter searches. However, the existence of the 4th
generation quarks and leptons should influence the production and decay rates
of Higgs boson and is ruled out by the experimental results of the Higgs boson
searches at the LHC, if the Higgs boson coupling to 4th generation fermions
with is not suppressed. Here we argue that the difference between the three
known quark-lepton families and the 4th family can naturally lead to
suppression of this coupling, relating the accelerator test for such a
composite dark matter scenario to the detailed study of the production and
modes of decay of the 125.5 GeV boson, discovered at the LHC.Comment: Prepared for the Special issue "Dark atoms and dark radiation" of
Advances in High Energy Physic
Remark on the minimal seesaw model and leptogenesis with tri/bi-maximal mixing
We have studied a leptogenesis scenario in the framework of the minimal
seesaw model with tri/bi-maximal mixing. Usually, at least one of the elements
in the Dirac mass matrix is fixed to be zero, for example, we denote it by
. We have pointed out that the absolute value of the CP asymmetry has
several minimums and maximums with non-zero . Thus one can expect that
more rich phenomena, such as an enhanced leptogenesis, are hidden in the space.Comment: 9 pages, 7 figures, uses RevTex4. To appear in Physcal Review
Dark matter from stable charged particles?
Particle physics candidates for cosmological dark matter are usually
considered as neutral and weakly interacting. However stable charged leptons
and quarks can also exist and, hidden in elusive atoms, play the role of dark
matter. The necessary condition for such scenario is absence of stable
particles with charge -1 and effective mechanism for suppression of free
positively charged heavy species. These conditions are realized in several
recently developed scenarios. In scenario based on Walking Technicolor model
excess of stable particles with charge -2 and the corresponding dark matter
density is naturally related with the value and sign of cosmological baryon
asymmetry. The excessive charged particles are bound with primordial helium in
techni-O-helium "atoms", maintaining specific nuclear-interacting form of dark
matter. Some properties of techni-O-helium Universe are discussed.Comment: Invited contribution to the book "Einstein and Hilbert: Dark Matter",
Ed. V.Dvoeglazo
Reheating temperature from the CMB
In the recent paper by Mielczarek \emph{et al.} (JCAP {\bf 1007} (2010) 004)
an idea of the method which can be used to put some constraint for the
reheating phase was proposed. Another method of constraining the reheating
temperature has been recently studied by Martin and Ringeval (Phys.\ Rev.\ D
{\bf 82} (2010) 023511). Both methods are based on observations of the cosmic
microwave background (CMB) radiation. In this paper, we develop the idea
introduced in this first article to put constraint on the reheating after the
slow-roll inflation. We restrict our considerations to the case of a massive
inflaton field. The method can be, however, easily extended to the different
inflationary scenarios. As a main result, we derive an expression on the
reheating temperature . Surprisingly, the obtained equation is
independent on the unknown number of relativistic degrees of freedom
produced during the reheating. Based on this equation and the WMAP 7
observations, we find GeV, which is consistent
with the current constraints. The relative uncertainty of the result is,
however, very high and equal to . As we show, this uncertainty will be significantly reduced with future CMB
experiments.Comment: 6 pages, 3 figures. Matches version published in Phys. Rev.
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