94 research outputs found
A m\'enage \`a trois of eV-scale sterile neutrinos, cosmology, and structure formation
We show that sterile neutrinos with masses ~1 eV or larger, as motivated by
several short-baseline oscillation anomalies, can be consistent with
cosmological constraints if they are charged under a hidden sector force
mediated by a light boson. In this case, sterile neutrinos experience a large
thermal potential that suppresses mixing between active and sterile neutrinos
in the early Universe, even if vacuum mixing angles are large. Thus, the
abundance of sterile neutrinos in the Universe remains very small, and their
impact on Big Bang Nucleosynthesis, Cosmic Microwave Background, and
large-scale structure formation is negligible. It is conceivable that the new
gauge force also couples to dark matter, possibly ameliorating some of the
small-scale structure problems associated with cold dark matter.Comment: 7 pages, 4 figures. v3: minor corrections in the discussion of small
scale structure led to the realization that all 3 problems can be solved
simultaneously. Matches PRL version titled "Cosmologically Safe eV-Scale
Sterile Neutrinos and Improved Dark Matter Structure". v4: references added,
calculations in appendix A rewritten in Feynman gauge. ArXiv version includes
2 additional figure
Temporal Instability Enables Neutrino Flavor Conversions Deep Inside Supernovae
We show that a self-interacting neutrino gas can spontaneously acquire a
non-stationary pulsating component in its flavor content, with a frequency that
can exactly cancel the "multi-angle" refractive effects of dense matter. This
can then enable homogeneous and inhomogeneous flavor conversion instabilities
to exist even at large neutrino and matter densities, where the system would
have been stable if the evolution were strictly stationary. Large flavor
conversions, especially close to a supernova core, are possible via this novel
mechanism. This may have important consequences for the explosion dynamics,
nucleosynthesis, as well as for neutrino observations of supernovae.Comment: v3: Improved Fig.1 and fixed typos. Matches version published in PR
Leptonic CP Violation Phases, Quark-Lepton Similarity and Seesaw Mechanism
We explore generic features of the leptonic CP violation in the framework of
the seesaw type I mechanism with similarity of the Dirac lepton and quarks mass
matrices . For this, we elaborate on the standard parametrization
conditions which allow to simultaneously obtain the Dirac and Majorana phases.
If the only origin of CP violation is the left-handed (LH) transformation which
diagonalizes (similar to quarks), the leptonic CP violation is suppressed
and the Dirac phase is close to or to with . Here , is the Cabibbo mixing
angle, and and are the 1-3 mixing angles of
quarks and leptons respectively. The Majorana phases and
are suppressed as . For Majorana neutrinos implied by
seesaw, the right-handed (RH) transformations are important. We explore the
simplest extension inspired by Left-Right (L-R) symmetry with small CKM-type CP
violation. In this case, seesaw enhancement of the CP violation occurs due to
strong hierarchy of the eigenvalues of leading to .
The enhancement is absent under the phase factorization conditions which
require certain relations between parameters of the Majorana mass matrix of RH
neutrinos.Comment: 30 pages. v3(typos fixed, matches version published in Nucl. Phys. B
Sterile Neutrinos with Secret Interactions - Lasting Friendship with Cosmology
Sterile neutrinos with mass ~1 eV and order 10% mixing with active neutrinos
have been proposed as a solution to anomalies in neutrino oscillation data, but
are tightly constrained by cosmological limits. It was recently shown that
these constraints are avoided if sterile neutrinos couple to a new MeV-scale
gauge boson A'. However, even this scenario is restricted by structure
formation constraints when A'-mediated collisional processes lead to efficient
active-to-sterile neutrino conversion after neutrinos have decoupled. In view
of this, we reevaluate in this paper the viability of sterile neutrinos with
such "secret" interactions. We carefully dissect their evolution in the early
Universe, including the various production channels and the expected
modifications to large scale structure formation. We argue that there are two
regions in parameter space - one at very small A' coupling, one at relatively
large A' coupling - where all constraints from big bang nucleosynthesis (BBN),
cosmic microwave background (CMB), and large scale structure (LSS) data are
satisfied. Interestingly, the large A' coupling region is precisely the region
that was previously shown to have potentially important consequences for the
small scale structure of dark matter halos if the A' boson couples also to the
dark matter in the Universe.Comment: 12 page
Fast neutrino flavor conversions near the supernova core with realistic flavor-dependent angular distributions
It has been recently pointed out that neutrino fluxes from a supernova can
show substantial flavor conversions almost immediately above the core. Using
linear stability analyses and numerical solutions of the fully nonlinear
equations of motion, we perform a detailed study of these fast conversions,
focussing on the region just above the supernova core. We carefully specify the
instabilities for evolution in space or time, andfind that neutrinos travelling
towards the core make fast conversions more generic, i.e., possible for a wider
range of flux ratios and angular asymmetries that produce a crossing between
the zenith-angle spectra of and . Using fluxes and angular
distributions predicted by supernova simulations, we find that fast conversions
can occur within tens of nanoseconds, only a few meters away from the putative
neutrinospheres. If these fast flavor conversions indeed take place, they would
have important implications for the supernova explosion mechanism and
nucleosynthesis.Comment: 18 pages, 7 figures (Improved presentation and new panel in Fig.6
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