135 research outputs found
Solar Neutrino Constraints on the BBN Production of Li
Using the recent WMAP determination of the baryon-to-photon ratio, 10^{10}
\eta = 6.14 to within a few percent, big bang nucleosynthesis (BBN)
calculations can make relatively accurate predictions of the abundances of the
light element isotopes which can be tested against observational abundance
determinations. At this value of \eta, the Li7 abundance is predicted to be
significantly higher than that observed in low metallicity halo dwarf stars.
Among the possible resolutions to this discrepancy are 1) Li7 depletion in the
atmosphere of stars; 2) systematic errors originating from the choice of
stellar parameters - most notably the surface temperature; and 3) systematic
errors in the nuclear cross sections used in the nucleosynthesis calculations.
Here, we explore the last possibility, and focus on possible systematic errors
in the He3(\alpha,\gamma)Be7 reaction, which is the only important Li7
production channel in BBN. The absolute value of the cross section for this key
reaction is known relatively poorly both experimentally and theoretically. The
agreement between the standard solar model and solar neutrino data thus
provides additional constraints on variations in the cross section (S_{34}).
Using the standard solar model of Bahcall, and recent solar neutrino data, we
can exclude systematic S_{34} variations of the magnitude needed to resolve the
BBN Li7 problem at > 95% CL. Additional laboratory data on
He3(\alpha,\gamma)Be7 will sharpen our understanding of both BBN and solar
neutrinos, particularly if care is taken in determining the absolute cross
section and its uncertainties. Nevertheless, it already seems that this
``nuclear fix'' to the Li7 BBN problem is unlikely; other possible solutions
are briefly discussed.Comment: 21 pages, 3 ps figure
Big Bang Nucleosynthesis and Particle Dark Matter
We review how our current understanding of the light element synthesis during
the Big Bang Nucleosynthesis era may help shed light on the identity of
particle dark matter.Comment: a mini-review for the NJP special issue on dark matte
HD/H2 Molecular Clouds in the Early Universe: The Problem of Primordial Deuterium
We have detected new HD absorption systems at high redshifts, z_abs=2.626 and
z_abs=1.777, identified in the spectra of the quasars J0812+3208 and Q1331+170,
respectively. Each of these systems consists of two subsystems. The HD column
densities have been determined: log(N(HD),A)=15.70+/-0.07 for z_A=2.626443(2)
and log(N(HD),B)=12.98+/-0.22 for z_B=2.626276(2) in the spectrum of J0812+3208
and log(N(HD),C)=14.83+/-0.15 for z_C=1.77637(2) and log(N(HD),D)=14.61+/-0.20
for z_D=1.77670(3) in the spectrum of Q1331+170. The measured HD/H2 ratio for
three of these subsystems has been found to be considerably higher than its
values typical of clouds in our Galaxy. We discuss the problem of determining
the primordial deuterium abundance, which is most sensitive to the baryon
density of the Universe \Omega_{b}. Using a well-known model for the chemistry
of a molecular cloud, we have estimated the isotopic ratio
D/H=HD/2H_2=(2.97+/-0.55)x10^{-5} and the corresponding baryon density
\Omega_{b}h^2=0.0205^{+0.0025}_{-0.0020}. This value is in good agreement with
\Omega_{b}h^2=0.0226^{+0.0006}_{-0.0006} obtained by analyzing the cosmic
microwave background radiation anisotropy. However, in high-redshift clouds,
under conditions of low metallicity and low dust content, hydrogen may be
incompletely molecularized even in the case of self-shielding. In this
situation, the HD/2H_2 ratio may not correspond to the actual D/H isotopic
ratio. We have estimated the cloud molecularization dynamics and the influence
of cosmological evolutionary effects on it
Lithium-6: A Probe of the Early Universe
I consider the synthesis of 6Li due to the decay of relic particles, such as
gravitinos or moduli, after the epoch of Big Bang Nucleosynthesis. The
synthesized 6Li/H ratio may be compared to 6Li/H in metal-poor stars which, in
the absence of stellar depletion of 6Li, yields significantly stronger
constraints on relic particle densities than the usual consideration of
overproduction of 3He. Production of 6Li during such an era of non-thermal
nucleosynthesis may also be regarded as a possible explanation for the
relatively high 6Li/H ratios observed in metal-poor halo stars.Comment: final version, Physical Review Letters, additional figure giving
limits on relic decaying particle
Precision Prediction for the Big-Bang Abundance of Primordial Helium
Within the standard models of particle physics and cosmology we have
calculated the big-bang prediction for the primordial abundance of \he to a
theoretical uncertainty of less than 0.1 \pct ,
improving the current theoretical precision by a factor of 10. At this accuracy
the uncertainty in the abundance is dominated by the experimental uncertainty
in the neutron mean lifetime, . The following
physical effects were included in the calculation: the zero and
finite-temperature radiative, Coulomb and finite-nucleon-mass corrections to
the weak rates; order- quantum-electrodynamic correction to the plasma
density, electron mass, and neutrino temperature; and incomplete neutrino
decoupling. New results for the finite-temperature radiative correction and the
QED plasma correction were used. In addition, we wrote a new and independent
nucleosynthesis code designed to control numerical errors to be less than
0.1\pct. Our predictions for the \EL[4]{He} abundance are presented in the form
of an accurate fitting formula. Summarizing our work in one number, . Further,
the baryon density inferred from the Burles-Tytler determination of the
primordial D abundance, , leads to the
prediction: . This ``prediction'' and an accurate measurement of the primeval \he
abundance will allow an important consistency test of primordial
nucleosynthesis.Comment: Replaced fitting formulas - new versions differ by small but
significant amount. Other minor changes. 30 pages, 17 figures, 5 table
Radiative Decay of a Long-Lived Particle and Big-Bang Nucleosynthesis
The effects of radiatively decaying, long-lived particles on big-bang
nucleosynthesis (BBN) are discussed. If high-energy photons are emitted after
BBN, they may change the abundances of the light elements through
photodissociation processes, which may result in a significant discrepancy
between the BBN theory and observation. We calculate the abundances of the
light elements, including the effects of photodissociation induced by a
radiatively decaying particle, but neglecting the hadronic branching ratio.
Using these calculated abundances, we derive a constraint on such particles by
comparing our theoretical results with observations. Taking into account the
recent controversies regarding the observations of the light-element
abundances, we derive constraints for various combinations of the measurements.
We also discuss several models which predict such radiatively decaying
particles, and we derive constraints on such models.Comment: Published version in Phys. Rev. D. Typos in figure captions correcte
The Effect of Bound Dineutrons upon BBN
We have examined the effects of a bound dineutron, n2, upon big bang
nucleosynthesis (BBN) as a function of its binding energy B_n2. We find a
weakly bound dineutron has little impact but as B_n2 increases its presence
begins to alter the flow of free nucleons to helium-4. Due to this disruption,
and in the absence of changes to other binding energies or fundamental
constants, BBN sets a reliable upper limit of B_n2 <~ 2.5 MeV in order to
maintain the agreement with the observations of the primordial helium-4 mass
fraction and D/H abundance
Quantifying uncertainties in primordial nucleosynthesis without Monte Carlo simulations
We present a simple method for determining the (correlated) uncertainties of
the light element abundances expected from big bang nucleosynthesis, which
avoids the need for lengthy Monte Carlo simulations. Our approach helps to
clarify the role of the different nuclear reactions contributing to a
particular elemental abundance and makes it easy to implement
energy-independent changes in the measured reaction rates. As an application,
we demonstrate how this method simplifies the statistical estimation of the
nucleon-to-photon ratio through comparison of the standard BBN predictions with
the observationally inferred abundances.Comment: 22 pages (RevTeX) incl. 8 figures (epsf); Changes: Figs. 5 & 6
combined + typo in Footnote 1 corrected + several stylistic changes; to
appear in Phys. Rev.
Bose-Einstein Condensation, Dark Matter and Acoustic Peaks
Scalar mediated interactions among baryons extend well above the Compton
wavelength, when they are embedded in a Bose-Einstein condensate composed of
the mediating particles. Indeed, this non-trivial environment results in an
infinite-ranged interaction. We show that if the Dark Matter of the Universe is
composed of such a condensate, the imprints of an interaction between baryonic
and Dark Matter could be manifest as anomalies in the peak structure of the
Cosmic Microwave Background.Comment: 11 pages, 2 figures; changes reflect published versio
Big Bang nucleosynthesis and physics beyond the Standard Model
The Hubble expansion of galaxies, the 2.73\dK blackbody radiation
background and the cosmic abundances of the light elements argue for a hot,
dense origin of the universe --- the standard Big Bang cosmology --- and enable
its evolution to be traced back fairly reliably to the nucleosynthesis era when
the temperature was of \Or(1) MeV corresponding to an expansion age of
\Or(1) sec. All particles, known and hypothetical, would have been created at
higher temperatures in the early universe and analyses of their possible
effects on the abundances of the synthesized elements enable many interesting
constraints to be obtained on particle properties. These arguments have
usefully complemented laboratory experiments in guiding attempts to extend
physics beyond the Standard SU(3)_{\c}{\otimes}SU(2)_{\L}{\otimes}U(1)_{Y}
Model, incorporating ideas such as supersymmetry, compositeness and
unification. We first present a pedagogical account of relativistic cosmology
and primordial nucleosynthesis, discussing both theoretical and observational
aspects, and then proceed to examine such constraints in detail, in particular
those pertaining to new massless particles and massive unstable particles.
Finally, in a section aimed at particle physicists, we illustrate applications
of such constraints to models of new physics.Comment: 156 pages LaTeX, including 18 PostScript figures; uses ioplppt.sty,
epsf, and personal style file (incl.); Revised and updated to include, e.g.
implications of new deuterium observations in primordial clouds; 2-up
PostScript version (78 pages) available at
ftp://ftp.physics.ox.ac.uk/pub/local/users/sarkar/BBNreview.ps.gz ; to appear
in Reports on Progress in Physic
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