721 research outputs found
How BAO measurements can fail to detect quintessence
We model the nonlinear growth of cosmic structure in different dark energy
models, using large volume N-body simulations. We consider a range of
quintessence models which feature both rapidly and slowly varying dark energy
equations of state, and compare the growth of structure to that in a universe
with a cosmological constant. The adoption of a quintessence model changes the
expansion history of the universe, the form of the linear theory power spectrum
and can alter key observables, such as the horizon scale and the distance to
last scattering. The difference in structure formation can be explained to
first order by the difference in growth factor at a given epoch; this scaling
also accounts for the nonlinear growth at the 15% level. We find that
quintessence models which feature late , rapid transitions towards
in the equation of state, can have identical baryonic acoustic
oscillation (BAO) peak positions to those in CDM, despite being very
different from CDM both today and at high redshifts .
We find that a second class of models which feature non-negligible amounts of
dark energy at early times cannot be distinguished from CDM using
measurements of the mass function or the BAO. These results highlight the need
to accurately model quintessence dark energy in N-body simulations when testing
cosmological probes of dynamical dark energy.Comment: 10 pages, 7 figures, to appear in the Invisible Univers International
Conference AIP proceedings serie
Yukawa Matrix for the Neutrino and Lepton Flavour Violation
We estimate the magnitude of Lepton Flavour Violation (LFV) from the phase of
the neutrino Yukawa matrix. In the minimal supersymmetric standard model with
right-handed neutrinos, the LFV processes l_i \to l_j \gamma can appear through
the slepton mixing, which comes from the renormalization group effect on the
right-handed neutrino Yukawa interaction between the Grand Unified Theory scale
and the heavy right-handed neutrino mass scale. Two types of phases exist in
the neutrino Yukawa matrix. One is the Majorana phase, which can change the
magnitude of the LFV branching ratios by a few factor. The other phases relate
for the size of the Yukawa hierarchy and its phase effect can change the LFV
branching ratios by several orders of magnitude.Comment: Talk given by K. Tsumura at NuFact04, Osaka, Japan, July 26 - August
1,2004 - 3 pages, 2 figure
Effects of Lightest Neutrino Mass in Leptogenesis
The effects of the lightest neutrino mass in ``flavoured'' leptogenesis are
investigated in the case when the CP-violation necessary for the generation of
the baryon asymmetry of the Universe is due exclusively to the Dirac and/or
Majorana phases in the neutrino mixing matrix U. The type I see-saw scenario
with three heavy right-handed Majorana neutrinos having hierarchical spectrum
is considered. The ``orthogonal'' parametrisation of the matrix of neutrino
Yukawa couplings, which involves a complex orthogonal matrix R, is employed.
Results for light neutrino mass spectrum with normal and inverted ordering
(hierarchy) are obtained. It is shown, in particular, that if the matrix R is
real and CP-conserving and the lightest neutrino mass m_3 in the case of
inverted hierarchical spectrum lies the interval 5 \times 10^{-4} eV < m_3 < 7
\times 10^{-3} eV, the predicted baryon asymmetry can be larger by a factor of
\sim 100 than the asymmetry corresponding to negligible m_3 \cong 0. As
consequence, we can have successful thermal leptogenesis for 5 \times 10^{-6}
eV < m_3 < 5 \times 10^{-2} eV even if R is real and the only source of
CP-violation in leptogenesis is the Majorana and/or Dirac phase(s) in U.Comment: 28 pages, 6 figures; published versio
MeV sterile neutrinos in low reheating temperature cosmological scenarios
It is commonly assumed that the cosmological and astrophysical bounds on the
mixings of sterile with active neutrinos are much more stringent than those
obtained from laboratory measurements. We point out that in scenarios with a
very low reheating temperature T_RH << 100 MeV at the end of (the last episode
of) inflation or entropy creation, the abundance of sterile neutrinos becomes
largely suppressed with respect to that obtained within the standard framework.
Thus, in this case cosmological bounds become much less stringent than usually
assumed, allowing sterile neutrinos to be ``visible'' in future experiments.
Here, we concentrate on massive (mostly sterile) neutrinos heavier than 1 MeV.Comment: 14 pp, 7 fig
Gravitational wave signatures from discrete flavor symmetries
Non-Abelian discrete symmetries have been widely used to explain the patterns of lepton masses and flavor mixing. In these models, a given symmetry is assumed at a high scale and then is spontaneously broken by scalars (the flavons), which acquire vacuum expectation values. Typically, the resulting leading order predictions for the oscillation parameters require corrections in order to comply with neutrino oscillation data. We introduce such corrections through an explicit small breaking of the symmetry. This has the advantage of solving the cosmological problems of these models without resorting to inflation. The explicit breaking induces an energy difference or "bias"between different vacua and drives the evolution of the domain walls, unavoidably produced after the symmetry breaking, towards their annihilation. Importantly, the wall annihilation leads to gravitational waves which may be observed in current and/or future experiments. We show that a distinctive pattern of gravitational waves with multiple overlapped peaks is generated when walls annihilate, which is within the reach of future detectors. We also show that cosmic walls from discrete flavor symmetries can be cosmologically safe for any spontaneous breaking scale between 1 and 1018 GeV, if the bias is chosen adequately, without the need to inflate the walls away. We use as an example a particular A4 model in which an explicit breaking is included in right-handed neutrino mass terms
Revisiting Leptogenesis in a SUSY SU(5) x T' Model of Flavour
We investigate the generation of the baryon asymmetry of the Universe within
a SUSY SU(5) x T' model of flavour, which gives rise to realistic masses and
mixing patterns for quarks and leptons. The model employs the see-saw mechanism
for generation of the light neutrino masses and the baryon asymmetry is
produced via leptogenesis. We perform detailed calculations of both the CP
violating lepton asymmetries, originating from the decays of the heavy Majorana
neutrinos operative in the see-saw mechanism, and of the efficiency factors
which account for the lepton asymmetry wash-out processes in the Early
Universe. The latter are calculated by solving numerically the system of
Boltzmann equations describing the generation and the evolution of the lepton
asymmetries. The baryon asymmetry in the model considered is proportional to
the J_{CP} factor, which determines the magnitude of CP violation effects in
the oscillations of flavour neutrinos. The leptogenesis scale can be
sufficiently low, allowing to avoid the potential gravitino problem.Comment: 14 pages, 1 figure; published versio
Investigation of double beta decay with the NEMO-3 detector
The double beta decay experiment NEMO~3 has been taking data since February
2003. The aim of this experiment is to search for neutrinoless
() decay and investigate two neutrino double beta decay in
seven different isotopically enriched samples (Mo, Se,
Ca, Zr, Cd, Te and Nd). After analysis of
the data corresponding to 3.75 y, no evidence for decay in the
Mo and Se samples was found. The half-life limits at the 90%
C.L. are y and y, respectively.
Additionally for decay the following limits at the 90% C.L.
were obtained, y for Ca, y
for Zr and y for Nd. The
decay half-life values were precisely measured for all investigated isotopes.Comment: 12 pages, 4 figures, 5 tables; talk at conference on "Fundamental
Interactions Physics" (ITEP, Moscow, November 23-27, 2009
Immunohistochemical localization of IGF-I, IGF-II and MSTN proteins during development of triploid sea bass (Dicentrarchus labrax)
The cellular localization of IGF-I, IGF-II and MSTN proteins was investigated during ontogenesis of triploid sea bass (Dicentrarchus labrax) by an immunohistochemical approach. The results were compared with those observed in diploids. IGF-I immunostaining was mainly observed in skin, skeletal muscle, intestine and gills of both diploids and triploids. From day 30 of larval life, IGF-I immunoreactivity observed in skeletal muscle, intestine, gills and kidney was stronger in triploids than in diploids. At day 30, triploids exhibited a standard length significantly higher than the one of diploids. Although IGF-II and MSTN immunoreactivity was detectable in different tissues and organs, no differences between diploids and triploids were observed. The spatial localization of IGF-I, IGF-II and MSTN proteins detected in this study is in agreement with previous findings on the distribution of these proteins in diploid larvae and fry. The highest IGF-I immunoreactivity observed in triploids suggests a possible involvement of ploidy in their growth performance
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