516 research outputs found
Flavor Physics in the Randall-Sundrum Model: I. Theoretical Setup and Electroweak Precision Tests
A complete discussion of tree-level flavor-changing effects in the
Randall-Sundrum (RS) model with brane-localized Higgs sector and bulk gauge and
matter fields is presented. The bulk equations of motion for the gauge and
fermion fields, supplemented by boundary conditions taking into account the
couplings to the Higgs sector, are solved exactly. For gauge fields the
Kaluza-Klein (KK) decomposition is performed in a covariant R_xi gauge. For
fermions the mixing between different generations is included in a completely
general way. The hierarchies observed in the fermion spectrum and the quark
mixing matrix are explained naturally in terms of anarchic five-dimensional
Yukawa matrices and wave-function overlap integrals. Detailed studies of the
flavor-changing couplings of the Higgs boson and of gauge bosons and their KK
excitations are performed, including in particular the couplings of the
standard W and Z bosons. A careful analysis of electroweak precision
observables including the S and T parameters and the Zbb couplings shows that
the simplest RS model containing only Standard Model particles and their KK
excitations is consistent with all experimental bounds for a KK scale as low as
a few TeV, if one allows for a heavy Higgs boson and/or for an ultra-violet
cutoff below the Planck scale. The study of flavor-changing effects includes
analyses of the non-unitarity of the quark mixing matrix, anomalous
right-handed couplings of the W bosons, tree-level flavor-changing neutral
current couplings of the Z and Higgs bosons, the rare decays t-->c(u)+Z and
t-->c(u)+h, and the flavor mixing among KK fermions. The results obtained in
this work form the basis for general calculations of flavor-changing processes
in the RS model and its extensions.Comment: 70 pages, 12 figures. v2: Incorrect treatment of phases in zero-mode
approximation corrected, and discussion of electroweak precision tests
modified. v3: Additional minor modifications and typos corrected; version
published in JHE
The warm circumstellar envelope and wind of the G9 IIb star HR 6902
IUE observations of the eclipsing binary system HR 6902 obtained at various
epochs spread over four years indicate the presence of warm circumstellar
material enveloping the G9 IIb primary. The spectra show Si IV and C IV
absorption up to a distance of 3.3 giant radii (R_g}. Line ratio diagnostics
yields an electron temperature of ~ 78000 K which appears to be constant over
the observed height range.
Applying a least square fit absorption line analysis we derive column
densities as a function of height. We find that the inner envelope (< 3 R_g) of
the bright giant is consistent with a hydrostatic density distribution. The
derived line broadening velocity of ~ 70 kms^{-1} is sufficient to provide
turbulent pressure support for the required scale height. However, an improved
agreement with observations over the whole height regime including the emission
line region is obtained with an outflow model. We demonstrate that the common
beta power-law as well as a P \propto rho wind yield appropriate fit models.
Adopting a continuous mass outflow we obtain a mass-loss rate of M_loss= (0.8 -
3.4)*10^{-11} M_{sun}yr^{-1} depending on the particular wind model.Comment: 11 pages, 8 figures, submitted to Astronomy Astrophysics main Journa
Dead Zone Accretion Flows in Protostellar Disks
Planets form inside protostellar disks in a dead zone where the electrical
resistivity of the gas is too high for magnetic forces to drive turbulence. We
show that much of the dead zone nevertheless is active and flows toward the
star while smooth, large-scale magnetic fields transfer the orbital angular
momentum radially outward. Stellar X-ray and radionuclide ionization sustain a
weak coupling of the dead zone gas to the magnetic fields, despite the rapid
recombination of free charges on dust grains. Net radial magnetic fields are
generated in the magneto-rotational turbulence in the electrically conducting
top and bottom surface layers of the disk, and reach the midplane by Ohmic
diffusion. A toroidal component to the fields is produced near the midplane by
the orbital shear. The process is similar to the magnetization of the Solar
tachocline. The result is a laminar, magnetically-driven accretion flow in the
region where the planets form.Comment: 12 pages, 4 figure
A Mechanism to Produce the Small Dust Observed in Protoplanetary Disks
Small (sub)-micron dust is present over the entire lifetime of protoplanetary
disks. As aggregation readily depletes small particles, one explanation might
be that dust is continuously generated by larger bodies in the midplane and
transported to the surface of the disks. In general, in a first step of this
scenario, the larger bodies have to be destroyed again and different mechanisms
exist with the potential to accomplish this. Possible destructive mechanisms
are fragmentation in collisions, erosion by gas drag or light induced erosion.
In laboratory experiments we find that the latter, light induced erosion by
Knudsen compression and photophoresis, can provide small particles. It might be
a preferred candidate as the dust is released into a low particle density
region. The working principle of this mechanism prevents or decreases the
likelihood for instant re-accretion or re-growth of large dense aggregates.
Provided that there is a particle lift, e.g. turbulence, these particles might
readily reach the surface of the disk.Comment: 7 pages, 6 figure
Recent developments in radiative B decays
We report on recent theoretical progress in radiative B decays. We focus on a
calculation of logarithmically enhanced QED corrections to the branching ratio
and forward-backward asymmetry in the inclusive rare decay anti-B --> X(s) l+
l-, and present the results of a detailed phenomenological analysis. We also
report on the calculation of NNLO QCD corrections to the inclusive decay anti-B
--> X(s) gamma. As far as exclusive modes are concerned we consider
transversity amplitudes and the impact of right-handed currents in the
exclusive anti-B --> K^* l+ l- decay. Finally, we state results for exclusive B
--> V gamma decays, notably the time-dependent CP-asymmetry in the exclusive B
--> K^* gamma decay and its potential to serve as a so-called ``null test'' of
the Standard Model, and the extraction of CKM and unitarity triangle parameters
from B --> (rho,omega) gamma and B --> K^* gamma decays.Comment: 5 pages, 2 figures. Accepted for publication in the proceedings of
International Europhysics Conference on High Energy Physics (EPS-HEP2007),
Manchester, England, 19-25 Jul 200
Updated NNLO QCD predictions for the weak radiative B-meson decays
Weak radiative decays of the B mesons belong to the most important flavor
changing processes that provide constraints on physics at the TeV scale. In the
derivation of such constraints, accurate standard model predictions for the
inclusive branching ratios play a crucial role. In the current Letter we
present an update of these predictions, incorporating all our results for the
O(alpha_s^2) and lower-order perturbative corrections that have been calculated
after 2006. New estimates of nonperturbative effects are taken into account,
too. For the CP- and isospin-averaged branching ratios, we find B_{s gamma} =
(3.36 +_ 0.23) * 10^-4 and B_{d gamma} = 1.73^{+0.12}_{-0.22} * 10^-5, for
E_gamma > 1.6GeV. Both results remain in agreement with the current
experimental averages. Normalizing their sum to the inclusive semileptonic
branching ratio, we obtain R_gamma = ( B_{s gamma} + B_{d gamma})/B_{c l nu} =
(3.31 +_ 0.22) * 10^-3. A new bound from B_{s gamma} on the charged Higgs boson
mass in the two-Higgs-doublet-model II reads M_{H^+} > 480 GeV at 95%C.L.Comment: journal version, 5 pages, no figure
Advances in the proposed electromagnetic zero-point field theory of inertia
A NASA-funded research effort has been underway at the Lockheed Martin
Advanced Technology Center in Palo Alto and at California State University in
Long Beach to develop and test a recently published theory that Newton's
equation of motion can be derived from Maxwell's equations of electrodynamics
as applied to the zero-point field (ZPF) of the quantum vacuum. In this
ZPF-inertia theory, mass is postulated to be not an intrinsic property of
matter but rather a kind of electromagnetic drag force that proves to be
acceleration dependent by virtue of the spectral characteristics of the ZPF.
The theory proposes that interactions between the ZPF and matter take place at
the level of quarks and electrons, hence would account for the mass of a
composite neutral particle such as the neutron. An effort to generalize the
exploratory study of Haisch, Rueda and Puthoff (1994) into a proper
relativistic formulation has been successful. Moreover the principle of
equivalence implies that in this view gravitation would also be electromagnetic
in origin along the lines proposed by Sakharov (1968). With regard to exotic
propulsion we can definitively rule out one speculatively hypothesized
mechanism: matter possessing negative inertial mass, a concept originated by
Bondi (1957) is shown to be logically impossible. On the other hand, the linked
ZPF-inertia and ZPF-gravity concepts open the conceptual possibility of
manipulation of inertia and gravitation, since both are postulated to be
electromagnetic phenomena. It is hoped that this will someday translate into
actual technological potential. A key question is whether the proposed
ZPF-matter interactions generating the phenomenon of mass might involve one or
more resonances. This is presently under investigation.Comment: Revised version of invited presentation at 34th AIAA/ASME/SAE/ASEE
Joint Propulsion Conference, July 13-15, 1998, Cleveland, OH, 10 pages, no
figure
Disks in the Arches cluster -- survival in a starburst environment
Deep Keck/NIRC2 HK'L' observations of the Arches cluster near the Galactic
center reveal a significant population of near-infrared excess sources. We
combine the L'-band excess observations with K'-band proper motions, to confirm
cluster membership of excess sources in a starburst cluster for the first time.
The robust removal of field contamination provides a reliable disk fraction
down to our completeness limit of H=19 mag, or about 5 Msun at the distance of
the Arches. Of the 24 identified sources with K'-L' > 2.0 mag, 21 have reliable
proper motion measurements, all of which are proper motion members of the
Arches cluster. VLT/SINFONI K'-band spectroscopy of three excess sources
reveals strong CO bandhead emission, which we interpret as the signature of
dense circumstellar disks. The detection of strong disk emission from the
Arches stars is surprising in view of the high mass of the B-type main sequence
host stars of the disks and the intense starburst environment. We find a disk
fraction of 6 +/- 2% among B-type stars in the Arches cluster. A radial
increase in the disk fraction from 3 to 10% suggests rapid disk destruction in
the immediate vicinity of numerous O-type stars in the cluster core. A
comparison between the Arches and other high- and low-mass star-forming regions
provides strong indication that disk depletion is significantly more rapid in
compact starburst clusters than in moderate star-forming environments.Comment: 51 pages preprint2 style, 22 figures, accepted by Ap
An Adaptive Optics Survey for Close Protostellar Binaries
In order to test the hypothesis that Class I protostellar binary stars are a
product of ejections during the dynamical decay of non-hierarchical multiple
systems, we combined the results of new adaptive optics (AO) observations of
Class I protostars with our previously published AO data to investigate whether
Class I protostars with a widely separated companion (r>200 AU) are more likely
to also have a close companion (r<200 AU). In total, we observed 47 embedded
young stellar objects (YSOs) with either the Subaru natural guide star AO
system or the Keck laser guide star AO system. We found that targets with a
widely separated companion within 5,000 AU are not more likely to have a close
companion. However, targets with another YSO within a projected separation of
25,000 AU are much more likely to have a close companion. Most importantly,
every target with a close companion has another YSO within a projected
separation of 25,000 AU. We came to the same conclusions after considering a
restricted sample of targets within 500 pc and close companions wider than 50
AU to minimize incompleteness effects. The Orion star forming region was found
to have an excess of both close binaries and YSOs within 25,000 AU compared to
other star forming regions. We interpret these observations as strong evidence
that many close Class I binary stars form via ejections and that many of the
ejected stars become unbound during the Class I phase.Comment: 22 pages, 3 figures, 2 table
The Evolution of the Multiplicity of Embedded Protostars II: Binary Separation Distribution & Analysis
We present the Class I protostellar binary separation distribution based on
the data tabulated in the companion paper. We verify the excess of Class I
binary stars over solar-type main-sequence stars, especially at separations
beyond 500 AU. Although our sources are in nearby star forming regions
distributed across the entire sky (including Orion), none of our objects are in
a high stellar density environment. The binary separation distribution changes
significantly during the Class I phase, and the binary frequency at separations
greater than 1000 AU declines steadily with respect to spectral index. Despite
these changes, the binary frequency remains constant until the end of the Class
I phase, when it drops sharply. We propose a scenario to account for the
changes in the Class I binary separation distribution. This scenario postulates
that companions with a separation greater than ~1000 AU were ejected during the
Class 0 phase, but remain gravitationally bound due to the mass of the
envelope. As the envelope dissipates, these companions become unbound and the
binary frequency at wide separations declines. This scenario predicts that a
large number of Class 0 objects should be non-hierarchical multiple systems,
and that many Class I YSOs with a widely separated companion should also have a
very close companion. We also find that Class I protostars are not dynamically
pristine, and have experienced dynamical evolution before they are visible as
Class I objects. For the first time, evidence is presented showing that the
Class I binary frequency and the binary separation distribution strongly depend
on the star forming environment. The reason for this dependence remains
unclear.Comment: 33 pages, 16 figures, accepted by the Astronomical Journa
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