6,950 research outputs found
Absence of a Lower Limit on Omega_b in Inhomogeneous Primordial Nucleosynthesis
We show that a class of inhomogeneous big bang nucleosynthesis models exist
which yield light-element abundances in agreement with observational
constraints for baryon-to-photon ratios significantly smaller than those
inferred from standard homogeneous big bang nucleosynthesis (HBBN). These
inhomogeneous nucleosynthesis models are characterized by a bimodal
distribution of baryons in which some regions have a local baryon-to-photon
ratio eta=3*10e-10, while the remaining regions are baryon-depleted. HBBN
scenarios with primordial (2H+3He)/H<9*10e-5 necessarily require that most
baryons be in a dark or non-luminous form, although new observations of a
possible high deuterium abundance in Lyman-alpha clouds may relax this
requirement somewhat. The models described here present another way to relax
this requirement and can even eliminate any lower bound on the baryon-to-photon
ratio.Comment: 13 pages, 2 figures (available upon request by email), plain te
Enhanced Heavy-Element Formation in Baryon-Inhomogeneous Big-Bang Models
We show that primordial nucleosynthesis in baryon inhomogeneous big-bang
models can lead to significant heavy-element production while still satisfying
all the light-element abundance constraints including the low lithium abundance
observed in population II stars. The parameters which admit this solution arise
naturally from the process of neutrino induced inflation of baryon
inhomogeneities prior to the epoch of nucleosynthesis. These solutions entail a
small fraction of baryons (\le 2\%) in very high density regions with local
baryon-to-photon ratio , while most baryons are at a
baryon-to-photon ratio which optimizes the agreement with light-element
abundances. The model would imply a unique signature of baryon inhomogeneities
in the early universe, evidenced by the existence of primordial material
containing heavy-element products of proton and alpha- burning reactions with
an abundance of .Comment: 19 pages in plain Tex, 5 figures (not included) available by fax or
mail upon request, ApJ in press, L
Vector boson production in association with KK modes of the ADD model to NLO in QCD at LHC
Next-to-leading order QCD corrections to the associated production of vector
boson (Z/W) with the the Kaluza-Klein modes of the graviton in large extra
dimensional model at the LHC, are presented. We have obtained various kinematic
distributions using a Monte Carlo code which is based on the two cut off phase
space slicing method that handles soft and collinear singularities appearing at
NLO level. We estimate the impact of the QCD corrections on various observables
and find that they are significant. We also show the reduction in factorization
scale uncertainty when QCD corrections are included.Comment: 12 pages, 5 figure
Baryonically Closed Galaxy Groups
Elliptical galaxies and their groups having the largest L_x/L_B lie close to
the locus in the L_x,L_B diagram expected for closed systems with baryon
fractions equal to the cosmic mean value, f_b = 0.16. The estimated baryon
fractions for several of these galaxies/groups are also close to 0.16 when the
gas density is extrapolated to the virial radius. Evidently they are the least
massive baryonically closed systems. Gas retention in these groups implies that
non-gravitational heating cannot exceed about 1 keV per particle, consistent
with the heating required to produce the deviation of groups from the L_x - T
correlation for more massive clusters. Isolated galaxies/groups with X-ray
luminosities significantly lower than baryonically closed groups may have
undermassive dark halos, overactive central AGNs, or higher star formation
efficiencies. The virial mass and hot gas temperatures of nearly or completely
closed groups correlate with the group X-ray luminosities and the optical
luminosities of the group-centered elliptical galaxy, an expected consequence
of their merging history. The ratio of halo mass to the mass of the central
galaxy for X-ray luminous galaxy/groups is about 80.Comment: 7 pages; Accepted by ApJ Letter
- âŠ