28 research outputs found
Mu-tau neutrino refraction and collective three-flavor transformations in supernovae
We study three-flavor collective neutrino transformations in the
dense-neutrino region above the neutrino sphere of a supernova core. We find
that two-flavor conversions driven by the atmospheric mass difference and the
13-mixing angle capture the full effect if one neglects the second-order
difference between the muon and tau neutrino refractive index. Including this
"mu-tau matter term" provides a resonance at a density of approximately 3 x
10^7 g cm^-3 that typically causes significant modifications of the overall
electron neutrino and antineutrino survival probabilities. This effect is
surprisingly sensitive to deviations from maximal 23-mixing, being different
for each octant.Comment: 9 pages, 7 figures. New presentation of results, version to be
published in PR
Decoherence in supernova neutrino transformations suppressed by deleptonization
In the dense-neutrino region at 50-400 km above the neutrino sphere in a
supernova, neutrino-neutrino interactions cause large flavor transformations.
We study when the multi-angle nature of the neutrino trajectories leads to
flavor decoherence between different angular modes. We consider a two-flavor
mixing scenario between nu_e and another flavor nu_x and assume the usual
hierarchy F(nu_e)>F{antinu_e)>F(nu_x)=F(antinu_x) for the number fluxes. We
define epsilon=(F(nu_e)-F(antinu_e))/(F(antinu_e)-F(antinu_x)) as a measure for
the deleptonization flux which is the one crucial parameter. The transition
between the quasi single-angle behavior and multi-angle decoherence is abrupt
as a function of epsilon. For typical choices of other parameters, multi-angle
decoherence is suppressed for epsilon>0.3, but a much smaller asymmetry
suffices if the neutrino mass hierarchy is normal and the mixing angle small.
The critical epsilon depends logarithmically on the neutrino luminosity. In a
realistic supernova scenario, the deleptonization flux is probably enough to
suppress multi-angle decoherence.Comment: 17 pages, 12 figures. Misprint in Eq (14) correcte
Collective flavor transitions of supernova neutrinos
We give a very brief overview of collective effects in neutrino oscillations in core collapse supernovae where refractive effects of neutrinos on themselves can considerably modify flavor oscillations, with possible repercussions for future supernova neutrino detection. We discuss synchronized and bipolar oscillations, the role of energy and angular neutrino modes, as well as three-flavor effects. We close with a short summary and some open questions.This work was supported by the Deutsche
Forschungsgemeinschaft (SFB 676 “Particles,
Strings and the Early Universe: The Structure
of Matter and Space-Time) and by the European
Union (contracts No. RII3-CT-2004-506222)
S_3-flavour symmetry as realized in lepton flavour violating processes
A variety of lepton flavour violating effects related to the recent discovery
of neutrino oscillations and mixings is here systematically discussed in terms
of an S_3-flavour permutational symmetry. After a brief review of some relevant
results on lepton masses and mixings, that had been derived in the framework of
a Minimal S_3-Invariant Extension of the Standard Model, we derive explicit
analytical expressions for the matrices of the Yukawa couplings and compute the
branching ratios of some selected flavour changing neutral current (FCNC)
processes, as well as, the contribution of the exchange of neutral flavour
changing scalars to the anomaly of the muon's magnetic moment as functions of
the masses of the charged leptons and the neutral Higgs bosons. We find that
the S_3 x Z_2 flavour symmetry and the strong mass hierarchy of the charged
leptons strongly suppress the FCNC processes in the leptonic sector well below
the present experimental upper bounds by many orders of magnitude. The
contribution of FCNC to the anomaly of the muon's magnetic moment is small but
non-negligible.Comment: 23 pages, one figure. To appear in J. Phys A: Mathematical and
Theoretical (SPE QTS5
Physics potential of future supernova neutrino observations
We point out possible features of neutrino spectra from a future galactic
core collapse supernova that will enhance our understanding of neutrino mixing
as well as supernova astrophysics. We describe the neutrino flavor conversions
inside the star, emphasizing the role of "collective effects" that has been
appreciated and understood only very recently. These collective effects change
the traditional predictions of flavor conversion substantially, and enable the
identification of neutrino mixing scenarios through signatures like Earth
matter effects.Comment: 8 pages, uses jpconf.cls. Talk given at Neutrino 2008, Christchurch,
NZ. Some entries in Table 2 have been correcte
Collective neutrino flavor transitions in supernovae and the role of trajectory averaging
Non-linear effects on supernova neutrino oscillations, associated with
neutrino self-interactions, are known to induce collective flavor transitions
near the supernova core for theta_13 \neq 0. In scenarios with very shallow
electron density profiles, these transformations have been shown to couple with
ordinary matter effects, jointly producing spectral distortions both in normal
and inverted hierarchy. In this work we consider a complementary scenario,
characterized by higher electron density, as indicated by post-bounce
shock-wave simulations. In this case, early collective flavor transitions are
decoupled from later, ordinary matter effects. Moreover, such transitions
become more amenable to both numerical computations and analytical
interpretations in inverted hierarchy, while they basically vanish in normal
hierarchy. We numerically evolve the neutrino density matrix in the region
relevant for self-interaction effects. In the approximation of averaged
intersection angle between neutrino trajectories, our simulations neatly show
the collective phenomena of synchronization, bipolar oscillations, and spectral
split, recently discussed in the literature. In the more realistic (but
computationally demanding) case of non-averaged neutrino trajectories, our
simulations do not show new significant features, apart from the smearing of
``fine structures'' such as bipolar nutations. Our results seem to suggest
that, at least for non-shallow matter density profiles, averaging over neutrino
trajectories plays a minor role in the final outcome. In this case, the swap of
nu_e and nu_{\mu,\tau} spectra above a critical energy may represent an
unmistakable signature of the inverted hierarchy, especially for theta_{13}
small enough to render further matter effects irrelevant.Comment: v2 (27 pages, including 9 eps figures). Typos removed, references
updated. Minor comments added. Corrected numerical errors in Eq.(6). Matches
the published versio
Non-standard interactions versus non-unitary lepton flavor mixing at a neutrino factory
The impact of heavy mediators on neutrino oscillations is typically described
by non-standard four-fermion interactions (NSIs) or non-unitarity (NU). We
focus on leptonic dimension-six effective operators which do not produce
charged lepton flavor violation. These operators lead to particular
correlations among neutrino production, propagation, and detection non-standard
effects. We point out that these NSIs and NU phenomenologically lead, in fact,
to very similar effects for a neutrino factory, for completely different
fundamental reasons. We discuss how the parameters and probabilities are
related in this case, and compare the sensitivities. We demonstrate that the
NSIs and NU can, in principle, be distinguished for large enough effects at the
example of non-standard effects in the --sector, which basically
corresponds to differentiating between scalars and fermions as heavy mediators
as leading order effect. However, we find that a near detector at superbeams
could provide very synergistic information, since the correlation between
source and matter NSIs is broken for hadronic neutrino production, while NU is
a fundamental effect present at any experiment.Comment: 32 pages, 5 figures. Final version published in JHEP. v3: Typo in Eq.
(27) correcte
Decoherence in supernova neutrino transformations suppressed by deleptonization
In the dense-neutrino region at 50–400 km above the neutrino sphere in a supernova, neutrino-neutrino interactions cause large flavor transformations. We study when the multi-angle nature of the neutrino trajectories leads to flavor decoherence between different angular modes. We consider a two-flavor mixing scenario between ν e and another flavor ν x and assume the usual hierarchy F ν e > F ν ¯ e > F ν x = F ν ¯ x for the number fluxe