999 research outputs found
The Relationship Between Galaxies and Low Redshift Weak Lyman alpha Absorbers in the Directions of H1821+643 and PG1116+215
To study the nature of low z Lya absorbers in the spectra of QSOs, we have
obtained high signal-to-noise UV spectra of H 1821+643 (z = 0.297) and PG
1116+215 (z = 0.177) with the GHRS on the HST. The spectra have minimum S/N of
70-100 and 3 sigma limiting equivalent widths of 50-75 mA. We detect 26 Lya
lines with Wr > 50 mA toward H1821+643 and 13 toward PG1116+215, which implies
a density of 102+/-16 lines per unit redshift. The two-point correlation
function shows marginal evidence of clustering on ~500 km/s scales, but only if
the weakest lines are excluded. We have also used the WIYN Observatory to
measure galaxy redshifts in the ~1 degree fields centered on each QSO. We find
17 galaxy-absorber pairs within projected distances of 1 Mpc with velocity
separations of 350 km/s or less. Monte Carlo simulations show that if the Lya
lines are randomly distributed, the probability of observing this many close
pairs is 3.6e-5. We find that all galaxies with projected distances of 600 kpc
or less have associated Lya absorbers within 1000 km/s, and the majority of
these galaxies have absorbers within 350 km/s. We also find that the Lya
equivalent width is anticorrelated with the projected distance of the nearest
galaxy out to at least 600 kpc, but this should be interpreted cautiously
because there are potential selection biases. Statistical tests using the
entire sample also indicate that the absorbers are not randomly distributed. We
discuss the nature of the Lya absorbers in light of the new data.Comment: Accepted for publication in ApJ. 17 pages plus 11 tables and 17
figure
Observing a column-dependent zeta in dense interstellar sources: the case of the Horsehead Nebula
Context: Observations of small carbon-bearing molecules such as CCH, C4H,
c-C3H2, and HCO in the Horsehead Nebula have shown these species to have higher
abundances towards the edge of the source than towards the center.
Aims: Given the determination of a wide range of values for zeta (s-1), the
total ionization rate of hydrogen atoms, and the proposal of a column-dependent
zeta(N_H), where N_H is the total column of hydrogen nuclei, we desire to
determine if the effects of zeta(N_H) in a single object with spatial variation
can be observable. We chose the Horsehead Nebula because of its geometry and
high density.
Method: We model the Horsehead Nebula as a near edge-on photon dominated
region (PDR), using several choices for zeta, both constant and as a function
of column. The column-dependent zeta functions are determined by a Monte Carlo
model of cosmic ray penetration, using a steep power-law spectrum and
accounting for ionization and magnetic field effects. We consider a case with
low-metal elemental abundances as well as a sulfur-rich case.
Results: We show that use of a column-dependent zeta(N_H) of 5(-15) s-1 at
the surface and 7.5(-16) s-1 at Av = 10 on balance improves agreement between
measured and theoretical molecular abundances, compared with constant values of
zeta.Comment: 12 pages, 6 figures, 5 tables, accepted in A&
Flavour in supersymmetric Grand Unification: a democratic approach
We consider the flavour problem in a supersymmetric Grand Unified theory with
gauged SU(6) group, where the Higgs doublets are understood as pseudo-Goldstone
bosons of a larger \SU(6)\otimes\SU(6) global symmetry of the Higgs
superpotential. A key element of this work is that we never appeal to any
flavour symmetry. One main interesting feature emerges: only one of the light
fermions, an up-type quark, to be identified with the top, can get a Yukawa
coupling at renormalizable level. This fact, together with bottom-tau Yukawa
unification, also implied in our scheme, gives rise to a characteristic
correlation between the top and the Higgs mass. By including a flavour-blind
discrete symmetry and requiring that all higher dimensional operators be
mediated by the exchange of appropriate heavy multiplets, it is possible to
give an approximate description of all masses and mixing angles in term of a
hierarchy of grand unified scales. A special ``texture'' arises, implying a
relation between the top mass and the third generation mixing angles. Several
other possible consequences of this approach are pointed out, concerning the
mass ratio, the Cabibbo angle and the proton decay.Comment: 14 pages, 4 figures in LaTeX, IFUP -- TH. 7/9
CO line emission in the halo of a radio galaxy at z=2.6
We report the detection of luminous CO(3-2) line emission in the halo of the
z=2.6 radio galaxy (HzRG) TXS0828+193, which has no detected counterpart at
optical to mid-infrared wavelengths implying a stellar mass < few x10^9 M_sun
and relatively low star-formation rates. With the IRAM PdBI we find two CO
emission line components at the same position at ~80 kpc distance from the HzRG
along the axis of the radio jet, with different blueshifts of few 100 km s^-1
relative to the HzRG and a total luminosity of ~2x10^10 K km s^-1 pc^2 detected
at 8 sigma significance. HzRGs have significant galaxy overdensities and
extended halos of metal-enriched gas often with embedded clouds or filaments of
denser material, and likely trace very massive dark-matter halos. The CO
emission may be associated with a gas-rich, low-mass satellite galaxy with
little on-going star formation, in contrast to all previous CO detections of
galaxies at similar redshifts. Alternatively, the CO may be related to a gas
cloud or filament and perhaps jet-induced gas cooling in the outer halo,
somewhat in analogy with extended CO emission found in low-redshift galaxy
clusters.Comment: MNRAS Letters, accepte
Octet magnetic moments and the Coleman-Glashow sum rule violation in the chiral quark model
Baryon octet magnetic moments when calculated within the chiral quark model,
incorporating the orbital angular momentum as well as the quark sea
contribution through the Cheng-Li mechanism, not only show improvement over the
non relativistic quark model results but also gives a non zero value for the
right hand side of Coleman-Glashow sum rule. When effects due to spin-spin
forces between constituent quarks as well as `mass adjustments' due to
confinement are added, it leads to an excellent fit for the case of p,
\Sigma^+, \Xi^o and violation of Coleman-Glashow sum rule, whereas in almost
all the other cases the results are within 5% of the data.Comment: 5 RevTeX pages, accepted for publication in PRD(Rapid Communication
Romantic ideals, mate preferences, and anticipation of future difficulties in marital life: a comparative study of young adults in India and America
This article has been made available through open access by the Brunel Open Access Publishing Fund.Previous studies have established that Indians tend to be greater in collectivism and gender role traditionalism than Americans. The purpose of the present study was to examine whether these differences explained further cultural differences in romantic beliefs, traditional mate preferences, and anticipation of future difficulties in marital life. Results revealed that Indians reported greater collectivism than Americans and, in turn, held stronger romantic beliefs. Additionally, Indians’ greater collectivism and endorsement of more traditional gender roles in part predicted their preferences for a marital partner possessing traditional characteristics, and fully accounted for their heightened concerns about encountering future difficulties in marital life. These results shed light on the processes underlying cultural differences in relationship attitudes and preferences, and point to culture-specific therapies to enhance marital functioning
The Intermediate Scale MSSM, the Higgs Mass and F-theory Unification
Even if SUSY is not present at the Electro-Weak scale, string theory suggests
its presence at some scale M_{SS} below the string scale M_s to guarantee the
absence of tachyons. We explore the possible value of M_{SS} consistent with
gauge coupling unification and known sources of SUSY breaking in string theory.
Within F-theory SU(5) unification these two requirements fix M_{SS} ~ 5 x
10^{10} GeV at an intermediate scale and a unification scale M_c ~ 3 x 10^{14}
GeV. As a direct consequence one also predicts the vanishing of the quartic
Higgs SM self-coupling at M_{SS} ~10^{11} GeV. This is tantalizingly consistent
with recent LHC hints of a Higgs mass in the region 124-126 GeV. With such a
low unification scale M_c ~ 3 x 10^{14} GeV one may worry about too fast proton
decay via dimension 6 operators. However in the F-theory GUT context SU(5) is
broken to the SM via hypercharge flux. We show that this hypercharge flux
deforms the SM fermion wave functions leading to a suppression, avoiding in
this way the strong experimental proton decay constraints. In these
constructions there is generically an axion with a scale of size f_a ~
M_c/(4\pi)^2 ~ 10^{12} GeV which could solve the strong CP problem and provide
for the observed dark matter. The prize to pay for these attractive features is
to assume that the hierarchy problem is solved due to anthropic selection in a
string landscape.Comment: 48 pages, 8 figures. v3: further minor correction
Parity-Violating Excitation of the \Delta(1232): Hadron Structure and New Physics
We consider prospects for studying the parity-violating (PV) electroweak
excitation of the \Delta(1232) resonance with polarized electron scattering.
Given present knowledge of Standard Model parameters, such PV experiments could
allow a determination of the N -> \Delta electroweak helicity amplitudes. We
discuss the experimental feasibility and theoretical interpretability of such a
determination as well as the prospective implications for hadron structure
theory. We also analyze the extent to which a PV N -> \Delta measurement could
constrain various extensions of the Standard Model.Comment: 43 pages, RevTex, 8 PS figures, uses epsf.sty, rotate.sty, version to
appear in Nucl. Phys. A, main points emphasized, some typos correcte
Reaction and Axial Vector Coupling
The reaction is studied in the region of low
to investigate the effect of deuteron structure and width of the
resonance on the differential cross section. The results are used to extract
the axial vector coupling from the experimental data on
this reaction. The possibility to determine this coupling from electroweak
interaction experiments with high intensity electron accelerators is discussed.Comment: 14 pages, REVTEX, 5 figure
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