Neutrino degeneracy and cosmological nucleosynthesis, revisited

Big Bang Nucleosynthesis (BBN) has increasingly become the tool of choice for investigating the permitted variation of fundamental constants during the earliest epochs of the Universe. Here we present a BBN calculation that has been modified to permit changes in the QCD scale, ΛQCD. The primary effects of changing the QCD scale upon BBN are through the deuteron binding energy, BD, and the neutron-proton mass difference, δmnp, which both play crucial roles in determining the primordial abundances. In this paper, we show how a simplified BBN calculation allows us to restrict the nuclear data we need to just BD and δmnp yet still gives useful results so that any variation in ΛQCD may be constrained via the corresponding shifts in BD and δmnp by using the current estimates of the primordial deuterium abundance and helium mass fraction. The simplification predicts the helium-4 and deuterium abundances to within 1% and 50% respectively when compared with the results of a standard BBN code. But ΛQCD also affects much of remaining required nuclear input so this method introduces a systematic error into the calculation and we find a degeneracy between BD and δmnp. We show how increased understanding of the relationship of the pion mass and/or BD to other nuclear parameters, such as the binding energy of tritium and the cross section of T + D → 4 He + n, would yield constraints upon any change in BD and δmnp at the 10% level.PACS numbers: 99.99

Section: Non-standard Bbnmentioning

confidence: 99%

Big bang nucleosynthesis andΛQCD

Kneller

McLaughlin

2003

“…We consider two representative cases of interest: first, the case where ξ e = 0 and ξ µ = ξ τ = 0, which is equivalent to ξ e ξ µ , ξ τ , and the case ξ e = ξ µ = ξ τ . The latter is probably the most physically realistic case [9,13]. Although we have discussed our linear programming procedure only for the case of ν e degeneracy, it generalizes in an obvious way for the case where ξ e = ξ µ = ξ τ .…”

Section: Nucleosynthesismentioning

confidence: 99%

Inhomogeneous neutrino degeneracy and big bang nucleosynthesis

Whitmire

Scherrer

2000

We examine Big Bang nucleosynthesis (BBN) in the case of inhomogenous neutrino degeneracy, in the limit where the fluctuations are sufficiently small on large length scales that the present-day element abundances are homogeneous. We consider two representive cases: degeneracy of the electron neutrino alone, and equal chemical potentials for all three neutrinos. We use a linear programming method to constrain an arbitrary distribution of the chemical potentials. For the current set of (highly-restrictive) limits on the primordial element abundances, homogeneous neutrino degeneracy barely changes the allowed range of the baryon-to-photon ratio η. Inhomogeneous degeneracy allows for little change in the lower bound on η, but the upper bound in this case can be as large as η = 1.1 × 10 −8 (only νe degeneracy) or η = 1.0 × 10 −9 (equal degeneracies for all three neutrinos).For the case of inhomogeneous neutrino degeneracy, we show that there is no BBN upper bound on the neutrino energy density, which is bounded in this case only by limits from structure formation and the cosmic microwave background.

“…Despite being decoupled from the photons and other leptons, neutrinos influenced nucleosynthesis through neutrino-nucleon interactions until the temperature dropped by about another factor of 2 and attained the "freeze-out" point Tf =0.7 MeV where neutrinos ceased to affect the neutron-proton ratio [4,5]. Subsequently Universe from a particular extension of the minimal standard model.…”

mentioning

confidence: 99%

Nonlinear neutrino oscillations in the expanding Universe

Samuel

1994

We derive the equations that govern neutrino and antineutrino behavior in the early Universe. Results are presented from numerical simulations incorporating nonlinear effects of the neutrinoantineutrino background as well as the leading CP-symmetric and CP-asymmetric terms arising from the interactions with electrons and positrons. A broad spectrum of neutrino and antineutrino behavior is observed, ranging from vacuumlike to smooth. Oscillations exhibiting self-maintained coherence also appear. We identify a variety of neutrino properties arising as a consequence of the nonlinear neutrino self-interactions. The nonlinear effects tend to suppress any CP asymmetry relative to the linear case.An analytical approximation scheme reproducing bulk neutrino behavior is described. We discuss some physical implications of our results. PACS number(s): 95.30. Cq, 12.15.Ff, 14.60.Pq