316 research outputs found
CP Asymmetry for Inclusive Decay in the Minimal Supersymmetric Standard Model
We study the inclusive rare decay in the supergravity
inspired Minimal Supersymmetric Standard Model and compute the CP-asymmetry in
the decay rates. We show that there exist two phenomenologically acceptable
sets of SUSY parameters: for one set the CP-asymmetry has the same (positive)
sign as in the Standard Model and lies in the range (5-45)% while for the other
set it is negative with values within -(2-21)%.Comment: 15 pages, uses axodraw.st
Inclusive Decay Rate for in Next-to-Leading Logarithmic Order and CP Asymmetry in the Standard Model
We compute the decay rate for the CKM-suppressed electromagnetic penguin
decay (and its charge conjugate) in NLO QCD, including
leading power corrections in and in the standard model. The
average branching ratio of the decay and its charge conjugate
is estimated to be in the range , obtained by varying the CKM-Wolfenstein parameters
and in the range and and taking into account other parametric dependence. In the stated
range of the CKM parameters, we find the ratio to lie in the range between 0.017 and 0.074.
Theoretical uncertainties in this ratio are found to be small. Hence, this
ratio is well suited to provide independent constraints on the CKM parameters.
The CP-asymmetry in the decay rates is found to be in the
range . Both the decay rates and CP asymmetry are measurable in
forthcoming experiments at factories and possibly at HERA-B.Comment: 17 pages including 7 postscript figures; uses epsfig; The changes
w.r.t the previous version are: A comment about the Bremsstrahlung
corrections is added as well as a note on the feasibility of the measurement
$B -> X_d gamma
Tree-level contribution to \bar{B} -> X_d gamma using fragmentation functions
We evaluate the most important tree-level contributions connected with the
b-> u \bar{u} d gamma transition to the inclusive radiative decay \bar{B}-> X_d
gamma using fragmentation functions. In this framework the singularities
arising from collinear photon emission from the light quarks (u, \bar{u} and d)
can be absorbed into the (bare) quark-to-photon fragmentation function. We use
as input the fragmentation function extracted by the ALEPH group from the
two-jet cross section measured at LEP, where one of the jets is required to
contain a photon. To get the quark-to-photon fragmentation function at the
fragmentation scale \mu_F \sim m_b, we use the evolution equation, which we
solve numerically. We then calculate the (integrated) photon energy spectrum
for b-> u \bar{u} d gamma related to the operators P^u_{1,2}. For comparison,
we also give the corresponding results when using nonzero (constituent) masses
for the light quarks.Comment: 13 pages, 4 figure
Forward--Backward Asymmetry in B -> X_s l^+ l^- at the NNLL Level
We report the results of a new calculation of soft-gluon corrections in B ->
X_s l^+ l^- decays. In particular, we present the first calculation of
bremsstrahlung and corresponding virtual terms to the lepton forward-backward
asymmetry, which allows us to systematically include all contributions to this
observable beyond the lowest non-trivial order. The new terms are important,
for instance the position of the zero of the asymmetry receives corrections of
O(10%). Using a different method, we also provide an independent check of
recently published results on bremsstrahlung and infrared virtual corrections
to the dilepton-invariant mass distribution.Comment: 20 pages, 5 figures. v2: typo in (4.26) corrected; discussion on
mu-dependence modifie
Running Neutrino Masses, Leptonic Mixing Angles and CP-Violating Phases: From to
We derive renormalization group equations for neutrino masses, leptonic
mixing angles and CP-violating phases running at energies above the seesaw
threshold, both in the Standard Model and in the Minimal Supersymmetric
Standard Model extended with three right-handed neutrinos. With these
equations, we carry out a systematic study of the radiative correction that may
arise to neutrino parameters, via their renormalization group evolution from
the electroweak scale () to the scale of Grand Unified theories
(). We study in detail three typically interesting neutrino
mass patterns: normal hierarchy, near degeneracy and inverted hierarchy.
Magnitudes of possible corrections in each case are carefully investigated. We
also emphasize the significance of CP-violating phases in controlling the
evolution behavior of all neutrino parameters.Comment: 45 pages, 2 tables, 10 figures; a misplaced graph in Figure 6
correcte
Fermionic corrections to the interference of the electro- and chromomagnetic dipole operators in anti-B --> X(s) gamma at O(alpha(s)**2)
We calculate the virtual and bremsstrahlung fermionic corrections due to the
interference of the electro- and chromomagnetic dipole operators in the
inclusive \bar{B}\to X_s\gamma decay at O(\alpha_s^2) and present analytical
results for both the total decay rate and the photon energy spectrum.Comment: 13 pages, uses axodraw.sty; minor changes, matches published versio
B->X_s l^+l^- in the MSSM at NNLO
We present the results of the calculation of QCD corrections to the matching
conditions for the Wilson coefficients of operators mediating the transition
b->s l^+l^- in the context of the MSSM. Within a scenario with decoupled heavy
gluino the calculated contributions together with those present already in the
literature allow for the first time a complete NNLO analysis of B->X_s l^+l^-.
We study the impact of the QCD corrections and the reduction of renormalization
scale dependencies for the dilepton invariant mass distribution and the
forward-backward asymmetry in the inclusive decay B->X_s l^+l^- restricting the
analysis to the "low-s" region and small values of tan(beta). The NNLO
calculation allows to decrease the theoretical uncertainties related to the
renormalization scale dependence below the size of supersymmetric effects in
B->X_s l^+l^- depending on their magnitude. While it will be difficult to
distinguish the MSSM expectations for the branching ratio from the Standard
Model ones, this can become possible in the dilepton invariant mass
distribution depending on the MSSM parameters and \hat{s}. In this respect the
position of the zero of the forward-backward asymmetry s_0 is even more
promising.Comment: 35 pages, 10 figure
Towards next-to-next-to-leading-log accuracy for the width difference in the system: fermionic contributions to order and
We calculate a class of three-loop Feynman diagrams which contribute to the
next-to-next-to-leading logarithmic approximation for the width difference
in the system. The considered diagrams
contain a closed fermion loop in a gluon propagator and constitute the order
, where is the number of light quarks. Our results entail
a considerable correction in that order, if is expressed in
terms of the pole mass of the bottom quark. If the scheme is
used instead, the correction is much smaller. As a result, we find a decrease
of the scheme dependence. Our result also indicates that the usually quoted
value of the NLO renormalization scale dependence underestimates the
perturbative error.Comment: We corrected a typographical mistake in Eq. (4.18), made larger axis
labels in Fig.2. Version accepted by JHE
New data on the peculiar galaxy MRK 273
Colorimetric and spectral investigations of Markarian 273 and its three neighbors were performed on the basis of direct ultraviolet blue visual (UBV) and spectral observations with the 2-m Tautenburg telescope and the 6-m telescope of the Special Astrophysical Observatory of the USSR Academy of Sciences. The results obtained suggest that this galaxy is a close system of two objects with active nuclei. The observed straight tail with a thermal emission character is probably the result of the interaction of these galaxies
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