Number Of Neutrino Flavors Research Articles

Spin-independent two-neutrino exchange potential with mixing and CP violation

We develop a new approach for calculating the spin-independent 2-neutrino exchange potential (2-NEP) between non-relativistic fermions which places emphasis on the neutrino vacuum state, an area of theoretical interest in recent years. The 2-NEP is a natural probe of fundamental issues of neutrino physics such as neutrino masses, flavor mixing, the number of neutrino flavors, neutrino nature (Dirac or Majorana), $CP$-violation, and the neutrino vacuum state. We explore the dependence of the 2-NEP on the mixing of neutrino mass states assuming normal and inverted mass ordering for nucleon-nucleon, nucleon-lepton, and lepton-lepton interactions, and the $CP$-violation phase in the neutrino mixing matrix.

Relic neutrinos: Physically consistent treatment of effective number of neutrinos and neutrino mass

We perform a model independent study of the neutrino momentum distribution at freeze-out, treating the freeze-out temperature as a free parameter. Our results imply that measurement of neutrino reheating, as characterized by the measurement of the effective number of neutrinos $N_\nu$, amounts to the determination of the neutrino kinetic freeze-out temperature within the context of the standard model of particle physics where the number of neutrino flavors is fixed and no other massless (fractional) particles arise. At temperatures on the order of the neutrino mass, we show how cosmic background neutrino properties i.e. energy density, pressure, particle density, are modified in a physically consistent way as a function of neutrino mass and $N_\nu$.

Neutrino Properties Probed by Lepton Number Violating Processes

Study of neutrino properties is nowadays one of the most active domains of research in physics. On the one hand, fundamental properties of the neutrinos like their absolute mass, their character (are they Dirac or Majorana particles?) and the number of neutrino flavors, are still unknown. On the other hand, the knowledge of these properties are of great importance since the neutrinos are very abundant in nature and play a key role in nuclear and particle physics, astrophysics and cosmology. In addition, the results of the neutrino oscillation experiments have convincingly showed that neutrinos have mass and mix, in contradiction to the initial assumptions of the Standard Model. In this context there is an increased interest in the study of the Lepton Number Violating (LNV) processes, since they are capable to decide on the above mentioned neutrino properties. Since recently, the neutrinoless double beta (0nββ) decay was considered the only process able to distinguish between Dirac or Majorana neutrinos and to give a hint on the absolute mass of the electron neutrino. At present, the increased luminosity of the LHC experiments at CERN makes it feasable the search for LNV processes at LHC as well. Besides the neutrino character, these studies can also shed light on the existence of other types of neutrinos (the sterile neutrinos), than the three known ones. In this paper, I make a brief review on our present knowledge about the neutrino properties and on the way they can be probed by LNV processes at low- and high-energies. Particularly, I refer to the 0nββ decay process and to the first attempts of searching of LNV processes in hadron collider experiments, particularly in LHC experiments at CERN-Geneva.

Neutrino–neutrino interactions and flavour mixing in dense matter

An algebraic approach to the neutrino propagation in dense media is presented. The Hamiltonian describing a gas of neutrinos interacting with each other and with background fermions is written in terms of the appropriate SU(N) operators, where N is the number of neutrino flavours. The evolution of the resulting many-body problem is formulated as a coherent-state path integral. Some commonly used approximations are shown to represent the saddle-point solution of the path integral for the full many-body system.

Cosmological implications of neutrinos

The lectures describe several cosmological effects produced by neutrinos. Upper and lower cosmological limits on neutrino mass are derived. The role that neutrinos may play in formation of large scale structure of the universe is described and neutrino mass limits are presented. Effects of neutrinos on cosmological background radiation and on big bang nucleosynthesis are discussed. Limits on the number of neutrino flavors and mass/mixing are given.

Relic neutrino asymmetries and big bang nucleosynthesis in a four neutrino model

Oscillations between ordinary and sterile neutrinos can generate large neutrino asymmetries in the early universe. These asymmetries can significantly affect big bang nucleosynthesis (BBN) through modification of nuclear reaction rates. We study this phenomenon within a model consisting of the three ordinary neutrinos plus one sterile neutrino that can be motivated by the neutrino anomalies and the dark matter problem. We calculate how the lepton asymmetries produced evolve at temperatures where they impact on BBN. The effect of the asymmetries on primordial helium production is determined, leading to an effective number of neutrino flavours during BBN of either about 2.7 or 3.1 depending on the sign of the lepton asymmetry.

Cosmological Dark Matter

The basic arguments for cosmological dark matter are reviewed. It is shown that the Big Bange Nucleosynthesis constraints on the cosmological baryon density, when compared with dynamical arguments, demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is nonbaryonic. The recent extragalactic deuterium observations as well as the other light element abundances were examined in detail as is the argument on the number of neutrino flavors. Arguments from recent MACHO/EROS observations of halo dark matter seem to imply that at least some of the dark baryons are in the halos of galaxies. Comparison of baryonic density arguments with recent x-ray cluster data is also made. Discussion of the interface of density and age arguments is also presented.

BIG BANG NUCLEOSYNTHESIS: AN UPDATE

The current status of big bang nucleosynthesis is reviewed with an emphasis on the comparison between the observational determination of the light element abundances of D , 3 He , 4 He and 7 Li and the predictions from theory. In particular, we present new analyses for 4 He and 7 Li . Implications for physics beyond the standard model are also discussed. In addition, limits on the effective number of neutrino flavors are updated.

Nucleosynthesis Constraints on the Number of Neutrino Flavors

Nucleosynthesis Constraints on the Number of Neutrino Flavors

Nucleosynthesis Constraints on the Number of Neutrino Flavors

Nucleosynthesis Constraints on the Number of Neutrino Flavors

A determination of the properties of the neutral intermediate vector boson Z 0

We report the results of first physics runs of the L3 detector at LEP. Based on 2538 hadron events, we determined the mass m z 0 and the width Γ z 0 of the intermediate vector boson Z 0 to be m z 0 =91.132±0.057 GeV (not including the 46 MeV LEP machine energy uncertainty) and Γ z 0 =2.588±0.137 GeV. We also determined Γ invisible=0.567±0.080 GeV, corresponding to 3.42±0.48 number of neutrino flavors. We also measured the muon pair cross section and determined the branching ratio Γ μμ = Γ h=0.056±0.006. The partial width of Z 0→e +e − is Γ ee=88±9±7 MeV.

NONEQUILIBRIUM DECAYS OF LIGHT PARTICLES AND PRIMORDIAL NUCLEOSYNTHESIS

Possible modifications of the standard big-bang nucleosynthesis scenario, which would loosen the bound on the number of neutrino flavors, are examined. A concrete model with light ((mx=O( MeV )) quasistable particles (τx~1 s ) decaying into [Formula: see text] is considered. If the decay products do not thermalize they shift the frozen neutron-to-proton ratio and respectively the abundance of the light element produced primordially. The direction of this shift depends on the parameters of the model. Correspondingly for the particular choice of these parameters the restrictions on the number of neutrino flavors may be considerably weakened.

Bounds on the neutrino mass from the dark matter in the universe

The problem of the missing matter in the Universe is reviewed and discussed in terms of massive neutrinos. The primordial abundances of light elements produced during the big bang nucleosynthesis can be used to determine firm bounds on the number of neutrino flavours and on the ratio of baryon to photon densities in the Universe. These limits imply that nonbaryonic matter is the dominant constituent of large-scale cosmic structures, being massive neutrinos the best guess for such a matter. In order that the Universe be closed, a value of the neutrino rest mass is derived, which agrees with the bounds obtained from the dynamics of galaxies and clusters of galaxies. It is also shown that density perturbations can hardly grow in a nucleon-dominated Universe, and massive neutrinos may be the seed for nucleon condensations. All these astrophysical and cosmological considerations suggest a lower and an upper bound of the neutrino rest mass.

Neutrino counting through pair production by muons

We calculate the cross section and scattered-muon distributions for the process ..mu..+Z..--> mu..+..nu..+nu-bar+Z, namely neutrino pair production by muons in the Coulomb field of a heavy nucleus. The cross section is a measure of the number of light-neutrino flavors, assuming the standard model, as previously recognized. The differential distributions of the scattered muon are needed to interpret any partial measurement (short of a total cross section) and also provide important consistency checks for an eventual experimental signal. Unfortunately, the predicted cross section is very small for a small number of flavors; also, the final muon energy peaks near zero so that the practical acceptance is reduced. A measurement of this cross section is therefore not foreseen in the near future, despite its interest. We also calculate the contribution expected from diffractive vector-meson production ..mu..+Z..--> mu..+V/sup 0/+Z with V/sup 0/..--> nu..nu-bar decay; the V/sup 0/ = psi contribution considerably exceeds the direct neutrino rate. However, the V/sup 0/ process yields a completely different muon spectrum and can be distinguished by this; it also offers an independent measure of the number of neutrino flavors.

Helium Synthesis, Neutrino Flavors, and Cosmological Implications

The problem of the production of helium in the big bang is reexamined in the light of several recent astrophysical observations. These data, and theoretical particle-physics considerations, lead to some important inconsistencies in the standard big-bang model and suggest that a more complicated picture is needed. Thus, recent constraints on the number of neutrino flavors, as well as constraints on the mean density (openness) of the universe, need not be valid.

Helium Synthesis, Neutrino Flavors, and Cosmological Implications

The problem of the production of helium in the big bang is reexamined in the light of several recent astrophysical observations. These data, and theoretical particle-physics considerations, lead to some important inconsistencies in the standard big-bang model and suggest that a more complicated picture is needed. Thus, recent constraints on the number of neutrino flavors, as well as constraints on the mean density (openness) of the universe, need not be valid.

Full quark-lepton correspondence within a multigenerationSU(2)L×U(1)-based model

A full quark-lepton correspondence is established without upsetting (a) the standard Weinberg-Salam model, (b) the cosmological limits on the number of neutrino flavors, and (c) the neutrino masslessness property to all orders of perturbation theory. All this is within a minimal multigeneration tight scheme which is anomaly-free, conserves lepton numbers, and gives rise to a proper Cabibbo structure. A natural fermionic mass hierarchy accompanies the suppression of the horizontal gauge interactions through an absolute minimum of a symmetric Higgs potential. The model predicts ${m}_{t}=14.7$ GeV, and suggests a smaller current-algebra mass for the charmed quark without contradicting the measured ${K}_{L}\ensuremath{-}{K}_{S}$ mass difference.

Constraints on cosmology and neutrino physics from big bang nucleosynthesis

view Abstract Citations (210) References (41) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Constraints on cosmology and neutrino physics from big bang nucleosynthesis. Yang, J. ; Schramm, D. N. ; Steigman, G. ; Rood, R. T. Abstract Calculations of primordial nucleosynthesis are performed and used to study the dependence of the predicted abundances on the number of neutrino flavors and the time variation of the gravitational constant. Constraints on the primordial abundance of He-4 are reviewed, and it is suggested that this abundance, Y, is not greater than about 0.25. Severe constraints are placed on the number of lepton flavors (i.e., the number of types of light two-component neutrino), the present nucleon density, and the time variation of the gravitational constant. Primordial abundances of D, He-3, He-4, and Li-7 are computed for several values of lepton number over a range of nucleon densities. The results are compared with the observed abundances of D and Li-7. It is concluded that the universe cannot be closed by nucleons. Publication: The Astrophysical Journal Pub Date: January 1979 DOI: 10.1086/156779 Bibcode: 1979ApJ...227..697Y Keywords: Abundance; Astronomical Models; Big Bang Cosmology; Neutrinos; Nuclear Fusion; Gravitational Constant; Helium; Light Elements; Nucleons; Astrophysics; Cosmology:Nucleosynthesis; Neutrinos:Nucleosynthesis full text sources ADS |