30,792 research outputs found
Vacuum-UV spectroscopy of interstellar ice analogs. II. Absorption cross-sections of nonpolar ice molecules
Dust grains in cold circumstellar regions and dark-cloud interiors at 10-20 K
are covered by ice mantles. A nonthermal desorption mechanism is invoked to
explain the presence of gas-phase molecules in these environments, such as the
photodesorption induced by irradiation of ice due to secondary ultraviolet
photons. To quantify the effects of ice photoprocessing, an estimate of the
photon absorption in ice mantles is required. In a recent work, we reported the
vacuum-ultraviolet (VUV) absorption cross sections of nonpolar molecules in the
solid phase. The aim was to estimate the VUV-absorption cross sections of
nonpolar molecular ice components, including CH4, CO2, N2, and O2. The column
densities of the ice samples deposited at 8 K were measured in situ by infrared
spectroscopy in transmittance. VUV spectra of the ice samples were collected in
the 120-160 nm (10.33-7.74 eV) range using a commercial microwave-discharged
hydrogen flow lamp. We found that, as expected, solid N2 has the lowest
VUV-absorption cross section, which about three orders of magnitude lower than
that of other species such as O2, which is also homonuclear. Methane (CH4) ice
presents a high absorption near Ly-alpha (121.6 nm) and does not absorb below
148 nm. Estimating the ice absorption cross sections is essential for models of
ice photoprocessing and allows estimating the ice photodesorption rates as the
number of photodesorbed molecules per absorbed photon in the ice.Comment: 9 pages, 6 figures, 7 table
A More Flavored Higgs boson in Supersymmetric models
A More flavored Higgs boson arises when the flavor structure encoded in SUSY
extensions of the SM is transmited to the Higgs sector. The flavor-Higgs
transmition mechanism can have a radiative or mixing origin, as it is
illustrated with several examples, and can produce interesting Higgs signatures
that can be probed at future high-energy colliders. Within the MSSM, the flavor
mediation mechanism can be of radiative type, as it is realized trhough
gaugino-slepton loops, which transmit the flavor structture of the
soft-breaking sector to the Higgs bosons. In particular we focus on evaluating
the contributions from the general trilinear terms to the lepton flavor
violating Higgs (LFV) vertices. On the other hand, as an example of flavor
mediation through mixing, we discuss an E_6 inspired multi-Higgs model, with an
abelian flavor symmetry, where LFV as well as lepton flavor conserving Higgs
effects are found to arise, though in this case at tree-level. We find that
Tevatron and LHC can provide information on the flavor structure of these
models through the detection of the LFV higgs mode h-> tau+mu, while NLC can
perform high-precision measurements of the LFC mode h-> tau tau.Comment: 17 pages, 5 tables, 3 figures; corrected mistake in last section,
results changed but conclusions remmai
Mixed symmetry localized modes and breathers in binary mixtures of Bose-Einstein condensates in optical lattices
We study localized modes in binary mixtures of Bose-Einstein condensates
embedded in one-dimensional optical lattices. We report a diversity of
asymmetric modes and investigate their dynamics. We concentrate on the cases
where one of the components is dominant, i.e. has much larger number of atoms
than the other one, and where both components have the numbers of atoms of the
same order but different symmetries. In the first case we propose a method of
systematic obtaining the modes, considering the "small" component as
bifurcating from the continuum spectrum. A generalization of this approach
combined with the use of the symmetry of the coupled Gross-Pitaevskii equations
allows obtaining breather modes, which are also presented.Comment: 11 pages, 16 figure
Testing models with non-minimal Higgs sector through the decay t->q+WZ
We study the contribution of charged Higgs boson to the rare decay of the top
quark t->q+WZ (q=d,s,b) in models with Higgs sector that includes doublets and
triplets. Higgs doublets are needed to couple charged Higgs with quarks,
whereas the Higgs triplets are required to generate the non-standard vertex HWZ
at tree-level. It is found that within a model that respect the custodial SU(2)
symmetry and avoids flavour changing neutral currents by imposing discrete
symmetries, the decay mode t->b+WZ, can reach a branching ratio of order
0.0178, whereas the decay modes t->(d,s)+WZ, can reach a similar branching
ratio in models where flavour changing neutral currents are suppressed by
flavour symmetries.Comment: Typeset using REVTEX and EPSF, 5 pag, 2 figure
Free Fields for Chiral 2D Dilaton Gravity
We give an explicit canonical transformation which transforms a generic
chiral 2D dilaton gravity model into a free field theory.Comment: LaTeX file, 4 pages, to appear in Phys. Rev.
The Luminosity Function of Low-Redshift Abell Galaxy Clusters
We present the results from a survey of 57 low-redshift Abell galaxy clusters
to study the radial dependence of the luminosity function (LF). The dynamical
radius of each cluster, r200, was estimated from the photometric measurement of
cluster richness, Bgc. The shape of the LFs are found to correlate with radius
such that the faint-end slope, alpha, is generally steeper on the cluster
outskirts. The sum of two Schechter functions provides a more adequate fit to
the composite LFs than a single Schechter function. LFs based on the selection
of red and blue galaxies are bimodal in appearance. The red LFs are generally
flat for -22 < M_Rc < -18, with a radius-dependent steepening of alpha for M_Rc
> -18. The blue LFs contain a larger contribution from faint galaxies than the
red LFs. The blue LFs have a rising faint-end component (alpha ~ -1.7) for M_Rc
> -21, with a weaker dependence on radius than the red LFs. The dispersion of
M* was determined to be 0.31 mag, which is comparable to the median measurement
uncertainty of 0.38 mag. This suggests that the bright-end of the LF is
universal in shape at the 0.3 mag level. We find that M* is not correlated with
cluster richness when using a common dynamical radius. Also, we find that M* is
weakly correlated with BM-type such that later BM-type clusters have a brighter
M*. A correlation between M* and radius was found for the red and blue galaxies
such that M* fades towards the cluster center.Comment: Accepted for publication in ApJ, 16 pages, 4 tables, 24 figure
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