4,927 research outputs found
Factorization and Endpoint Singularities in Heavy-to-Light decays
We prove a factorization theorem for heavy-to-light form factors. Our result
differs in several important ways from previous proposals. A proper separation
of scales gives hard kernels that are free of endpoint singularities. A general
procedure is described for including soft effects usually associated with the
tail of wavefunctions in hard exclusive processes. We give an operator
formulation of these soft effects using the soft-collinear effective theory,
and show that they appear at the same order in the power counting as the hard
spectator contribution.Comment: 5 pages, Added details on comparison with the literatur
NEOWISE-R Observation of the Coolest Known Brown Dwarf
The Wide-field Infrared Survey Explorer (WISE) spacecraft has been
reactivated as NEOWISE-R to characterize and search for Near Earth Objects. The
brown dwarf WISE J085510.83-071442.5 has now been reobserved by NEOWISE-R, and
we confirm the results of Luhman (2014b), who found a very low effective
temperature ( K), a very high proper motion (8.1 +/- 0.1
arcsec/yr) , and a large parallax (454 +/- 45 mas). The large proper motion has
separated the brown dwarf from the background sources that influenced the 2010
WISE data, allowing a measurement of a very red WISE color of W1-W2
mag. A re-analysis of the 2010 WISE astrometry using only the W2 band, combined
with the new NEOWISE-R 2014 position, gives an improved parallax of 448 +/- 33
mas and proper motion of 8.08 +/- 0.05\; arcsec/yr. These are all consistent
with Luhman (2014b).Comment: 6 pages, AJ accepte
Investigations into the Influence of Chronic Colitis on Colonic Adenocarcinoma Cell Growth A Progress Report
Graduate
Basi
Form factors of heavy-to-light B decays at large recoil
General relations between the form factors of B decays to light mesons are
derived using the heavy quark and large recoil expansion. On their basis the
complete account of contributions of second order in the ratio of the light
meson mass to the large recoil energy is performed. Both ground and excited
final meson states are considered. It is shown that most of the known form
factor relations remain valid after the inclusion of quadratic mass
corrections. The validity of some of such relations requires additional
equalities for the helicity amplitudes. It is found that all these relations
and equalities are fulfilled in the relativistic quark model based on the
quasipotential approach in quantum field theory. The contribution of 1/m_b
corrections to the branching fraction of the rare radiative B decay is
discussed.Comment: 23 pages, revte
Semi-major Axis Jumps as the Activity Trigger in Centaurs and High-Perihelion Jupiter Family Comets
We present a dynamical study of 39 active Centaurs and 17 high-perihelion
(q4.5 au) JFCs with a focus on investigating recent orbital changes as
potential triggers for comet-like activity. We have identified a common feature
in the recent dynamical histories of all active Centaurs and JFC in our sample
that is not present in the history of the majority of inactive population
members: a sharp decrease in semi-major axis and eccentricity occurring within
the last several hundred years prior to observed activity. We define these
rapid orbital changes as `a-jumps'. Our results indicate that these orbital
reshaping events lead to shorter orbital periods and subsequently greater
average per-orbit heating of Centaur nuclei. We suggest the a-jumps could
therefore be a major trigger of cometary activity on Centaurs and JFCs. Our
results further imply that analyses of the recent dynamical histories could be
used to identify objects that are currently active or may become active soon,
where we have identified three such Centaurs with recent a-jumps that should be
considered high-priority targets for observational monitoring to search for
activity.Comment: 19 pages, 4 figures, 1 table, accepted for publication in ApJ
Measuring in Decays
We consider the possibility of measuring both and in the KM unitarity triangle using the process . This decay mode has a higher branching fraction (O(1%)) than
the mode . We use the factorization assumption and heavy
hadron chiral perturbation theory to estimate the branching fraction and
polarization. The time dependent rate for can be
used to measure and . Furthermore, examination
of the mass spectrum may be the best way to experimentally find
the broad p-wave meson.Comment: Revtex, 28 pages, 7 figures, title changed, introduction expanded,
added references, details of calculations moved to the appendi
Spinocerebellar ataxia types 1, 2, 3, and 6: disease severity and nonataxia symptoms.
OBJECTIVE: To identify factors that determine disease severity and clinical
phenotype of the most common spinocerebellar ataxias (SCAs), we studied 526
patients with SCA1, SCA2, SCA3. or SCA6.
METHODS: To measure the severity of ataxia we used the Scale for the Assessment
and Rating of Ataxia (SARA). In addition, nonataxia symptoms were assessed with
the Inventory of Non-Ataxia Symptoms (INAS). The INAS count denotes the number of
nonataxia symptoms in each patient.
RESULTS: An analysis of covariance with SARA score as dependent variable and
repeat lengths of the expanded and normal allele, age at onset, and disease
duration as independent variables led to multivariate models that explained 60.4%
of the SARA score variance in SCA1, 45.4% in SCA2, 46.8% in SCA3, and 33.7% in
SCA6. In SCA1, SCA2, and SCA3, SARA was mainly determined by repeat length of the
expanded allele, age at onset, and disease duration. The only factors determining
the SARA score in SCA6 were age at onset and disease duration. The INAS count was
5.0 +/- 2.3 in SCA1, 4.6 +/- 2.2 in SCA2, 5.2 +/- 2.5 in SCA3, and 2.0 +/- 1.7 in
SCA6. In SCA1, SCA2, and SCA3, SARA score and disease duration were the strongest
predictors of the INAS count. In SCA6, only age at onset and disease duration had
an effect on the INAS count.
CONCLUSIONS: Our study suggests that spinocerebellar ataxia (SCA) 1, SCA2, and
SCA3 share a number of common biologic properties, whereas SCA6 is distinct in
that its phenotype is more determined by age than by disease-related factors
Rare radiative B decays to orbitally excited K mesons
The exclusive rare radiative B meson decays to orbitally excited axial-vector
mesons K_1^*(1270), K_1(1400) and to the tensor meson K_2^*(1430) are
investigated in the framework of the relativistic quark model based on the
quasipotential approach in quantum field theory. These decays are considered
without employing the heavy quark expansion for the s quark. Instead the s
quark is treated to be light and the expansion in inverse powers of the large
recoil momentum of the final K^{**} meson is used to simplify calculations. It
is found that the ratio of the branching fractions of rare radiative B decays
to axial vector K^*_1(1270) and K_1(1400) mesons is significantly influenced by
relativistic effects. The obtained results for B decays to the tensor meson
K_2^*(1430) agree with recent experimental data from CLEO.Comment: 17 pages, revte
Exploring CP Violation through Correlations in B --> pi K, B_d --> pi^+pi^-, B_s --> K^+K^- Observable Space
We investigate allowed regions in observable space of B --> pi K, B_d -->
pi^+pi^- and B_s --> K^+K^- decays, characterizing these modes in the Standard
Model. After a discussion of a new kind of contour plots for the
system, we focus on the mixing- induced and direct CP asymmetries of the decays
B_d --> pi^+pi^- and B_s--> K^+K^-. Using experimental information on the
CP-averaged B_d --> pi^{+/-}K^{+/-} and B_d --> pi^+pi^- branching ratios, the
relevant hadronic penguin parameters can be constrained,implying certain
allowed regions in observable space. In the case of B_d --> pi^+pi^-, an
interesting situation arises now in view of the recent B-factory measurements
of CP violation in this channel, allowing us to obtain new constraints on the
CKM angle gamma as a function of the B^0_d--\bar{B^0_d} mixing phase
phi_d=2beta, which is fixed through A_{CP}^{mix}(B_d --> J/psi K_S) up to a
twofold ambiguity. If we assume that A_{CP}^{mix}(B_d --> pi^+pi^-) is
positive, as indicated by recent Belle data, and that phi_d is in agreement
with the ``indirect'' fits of the unitarity triangle, also the corresponding
values for gamma around 60 degrees can be accommodated. On the other hand, for
the second solution of phi_d, we obtain a gap around gamma ~ 60 degrees. The
allowed region in the space of A_{CP}^{mix}(B_s --> K^+K^-) and
A_{CP}^{dir}(B_s --> K^+K^-) is very constrained in the Standard Model, thereby
providing a narrow target range for run II of the Tevatron and the experiments
of the LHC era.Comment: 34 pages, LaTeX, 12 figures. More detailed introduction and a few
Comments added, conclusions unchanged. To appear in Phys. Rev.
: Status and Prospects
Several years ago, it was pointed out that the U-spin-related decays
, and , offer interesting strategies for the extraction of the angle gamma of
the unitarity triangle. Using the first results from the Tevatron on the
decays and the B-factory data on modes, we compare the determinations
of gamma from both strategies, study the sensitivity on U-spin-breaking
effects, discuss the resolution of discrete ambiguities, predict observables
that were not yet measured but will be accessible at LHCb, explore the
extraction of the width difference from untagged rates, and address the impact of new physics. The data for the
, system favour the BaBar measurement of
direct CP violation in , which will be used in the numerical
analysis, and result in a fortunate situation, yielding
, where the latter errors correspond
to a generous estimate of U-spin-breaking effects. On the other hand, the
, analysis leaves us with
, and points to a value of the branching ratio that is larger than the current Tevatron result. An
important further step will be the measurement of mixing-induced CP violation
in , which will also allow us to extract the -- mixing phase unambiguously with the help of at the
LHC. Finally, the measurement of direct CP violation in will
make the full exploitation of the physics potential of the modes possible.Comment: 28 pages, 10 figure
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