1,530 research outputs found
Time Dependent Quark Masses and Big Bang Nucleosynthesis Revisited
We reinvestigate the constraints from primordial nucleosynthesis on a
possible time-dependent quark mass. The limits on such quark-mass variations
are particularly sensitive to the adopted observational abundance constraints.
Hence, in the present study we have considered updated light-element abundances
and uncertainties deduced from observations. We also consider new nuclear
reaction rates and an independent analysis of the influence of such quark-mass
variations on the resonance properties of the important 3He(d,p)4He reaction.
We find that the updated abundance and resonance constraints imply a narrower
range on the possible quark-mass variations in the early universe. We also find
that, contrary to previous investigations, the optimum concordance region
reduces to a (95% C.L.) value of -0.005 < delta m_q/m_q < 0.007 consistent with
no variation in the averaged quark mass.Comment: 9 pages, 2 figures, analytic formulae of D and 4He abundances as well
as standard BBN prediction added, discussion on the 6Li production added,
minor errors fixed, accepted for publication in PR
Spectral function of the spiral spin state in the trestle and ladder Hubbard model
Eder and Ohta have found a violation of the Luttinger rule in the spectral
function for the t-t'-J model, which was interpreted as a possible breakdown of
the Tomonaga-Luttinger(TL) description in models where electrons can pass each
other. Here we have computed the spin correlation along with the spectral
function for the one-dimensional t-t' Hubbard model and two-leg Hubbard ladder.
By varying the Hubbard U we have identified that such a phenomenon is in fact a
spinless-fermion-like behavior of holes moving in a spiral spin configuration
that has a spin correlation length of the system size.Comment: 3 pages, RevTex, 8 figures in Postscript, to be published in Phys.
Rev. B (rapid communication
A Simultaneous Solution to the ^6Li and ^7Li Big Bang Nucleosynthesis Problems from a Long-Lived Negatively-Charged Leptonic Particle
The Li abundance observed in metal poor halo stars exhibits a plateau
similar to that for Li suggesting a primordial origin. However, the
observed abundance of Li is a factor of larger and that of Li is
a factor of 3 lower than the abundances predicted in the standard big bang when
the baryon-to-photon ratio is fixed by WMAP. Here we show that both of these
abundance anomalies can be explained by the existence of a long-lived massive,
negatively-charged leptonic particle during nucleosynthesis. Such particles
would capture onto the synthesized nuclei thereby reducing the reaction Coulomb
barriers and opening new transfer reaction possibilities, and catalyzing a
second round of big bang nucleosynthesis. This novel solution to both of the Li
problems can be achieved with or without the additional effects of stellar
destruction.Comment: 6 pages, 2 figures, to be published in Physical Review
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