152 research outputs found
Complete gluon bremsstrahlung corrections to the process b -> s l+ l-
In a recent paper, we presented the calculation of the order (alpha_s)
virtual corrections to b->s l+ l- and of those bremsstrahlung terms which are
needed to cancel the infrared divergences. In the present paper we work out the
remaining order(alpha_s) bremsstrahlung corrections to b->s l+ l- which do not
suffer from infrared and collinear singularities. These new contributions turn
out to be small numerically. In addition, we also investigate the impact of the
definition of the charm quark mass on the numerical results.Comment: 20 pages including 11 postscript figure
Direct CP-asymmetry in Inclusive Rare B-decays in 2HDM
The direct CP-asymmetry in the inclusive and decays is investigated in the two-Higgs doublet extension of the
Standard Model (2HDM). The investigation is performed in the lowest
non-vanishing order of the perturbation theory using the existing restrictions
on the 2HDM parameters space. It is shown that the direct CP-asymmetry in the
decay can deviate significantly from the Standard Model
predictions. In the presence of only one source of CP-violation (the CKM matrix
weak phase) can have the sign opposite to that in
the SM. The new source of CP-violation can make
arbitrary small (unlike the SM case) and hence unmeasurable. Quantitatively,
the obtained results suffer from the uncertainty of the choice of
renormalization scale. As for the rate asymmetry, its
renormalization scale dependence in the lowest non-vanishing order does not
allow to conclude if this quantity is efficient for testing New Physics beyond
the Standard Model.Comment: 16 pages including 2 figure
Calculation of two-loop virtual corrections to b --> s l+ l- in the standard model
We present in detail the calculation of the virtual O(alpha_s) corrections to
the inclusive semi-leptonic rare decay b --> s l+ l-. We also include those
O(alpha_s) bremsstrahlung contributions which cancel the infrared and mass
singularities showing up in the virtual corrections. In order to avoid large
resonant contributions, we restrict the invariant mass squared s of the lepton
pair to the range 0.05 < s/mb^2 < 0.25. The analytic results are represented as
expansions in the small parameters s/mb^2, z = mc^2/mb^2 and s/(4 mc^2). The
new contributions drastically reduce the renormalization scale dependence of
the decay spectrum. For the corresponding branching ratio (restricted to the
above s-range) the renormalization scale uncertainty gets reduced from +/-13%
to +/-6.5%.Comment: 41 pages including 9 postscript figures; in version 2 some typos and
inconsistent notation correcte
More Model-Independent Analysis of b->s Processes
We study model-independently the implications of non-standard scalar and
pseudoscalar interactions for the decays b ->s gamma, b -> s g, b -> s l^+l^-
(l=e,mu) and B_s -> mu^+ mu^-. We find sizeable renormalization effects from
scalar and pseudoscalar four-quark operators in the radiative decays and at
O(alpha_s) in hadronic b decays. Constraints on the Wilson coefficients of an
extended operator basis are worked out. Further, the ratios R_H = BR(B -> H
mu^+ mu^-)/BR(B -> H e^+ e^-), for H=K^(*), X_s, and their correlations with
B_s -> mu^+ mu^- decay are investigated. We show that the Standard Model
prediction for these ratios defined with the same cut on the dilepton mass for
electron and muon modes, R_H= 1 + O(m^2_mu/m^2_b), has a much smaller
theoretical uncertainty (<1%) than the one for the individual branching
fractions. The present experimental limit R_K < 1.2 puts constraints on scalar
and pseudoscalar couplings, which are similar to the ones from current data on
BR(B_s -> mu^+ mu^-). We find that new physics corrections to R_{K*} and
R_{X_s} can reach 13% and 10%, respectively.Comment: 28 pages, 6 figures; Table 1 updated, two refs added (to appear in
PRD
NNLL corrections to the angular distribution and to the forward-backward asymmetries in b -> X_s l+ l-
We present NNLL results for the double differential decay width dGamma(b ->
X_s l+ l-)/(dsh dcos(theta)), where theta is the angle between the momenta of
the b-quark and the l+, measured in the rest-frame of the lepton pair. From
these results we also derive NNLL results for the lepton forward-backward
asymmetries. Genuinely new calculations for the combined virtual- and gluon
bremsstrahlung corrections associated with the operators O_7, O_9 and O_10 are
necessary. We find that the NNLL corrections drastically reduce the
renormalization scale dependence of the forward-backward asymmetries. In
particular, sh_0, the position at which the forward-backward asymmetries
vanish, is essentially free of uncertainties due to the renormalization scale
at NNLL precision. We find sh_0(NNLL)=0.162 +/- 0.005, where the error is
dominated by the uncertainty in (m_c/m_b). This is to be compared with
sh_0(NLL)=0.144 +/- 0.020, where the error is dominated by uncertainties due to
the choice of mu.Comment: 26 pages including 11 postscript figure
Integrated stratigraphy of the Priabonian (upper Eocene) Urtsadzor section, Armenia
The transition from the Bartonian to the Priabonian, as traditionally understood, has long been associated with a series of extinctions and originations in several microfossil groups. The planktonic foraminifer genus Morozovelloides and large species of Acarinina suffered a rapid global extinction, as did many radiolarians. Calcareous nannofossils show several assemblage changes including the acme beginning of Cribrocentrum erbae and the lowest and highest occurrences of Chiasmolithus oamaruensis and C. grandis respectively. In shallow water environments, larger foraminifera also show an extinction among large species of Nummulites, as well as the first occurrences of the stratigraphically important genus Spiroclypeus. However, the correlation between shallow and deep water records remains uncertain, as do the mechanisms driving these biotic events. Here we present the results of a new integrated stratigraphical study (calcareous nannofossils, planktonic foraminifera, larger benthic foraminifera, and low-resolution magnetostratigraphy) of the Urtsadzor section in south-western Armenia which appears to be continuous through this interval. The Urtsadzor section consists of calcareous siltstones rich in micro- and nannofossils, with interbedded limestones containing abundant larger benthic foraminifera. Our new data enable us to correlate larger foraminiferal events with global plankton biostratigraphy, in a section outside of southwest Europe where most previous correlations have been based. At Urtsadzor, the large Nummulites species of N. millecaput-group are present throughout the whole section but decrease in abundance toward the top. The first occurrence of Spiroclypeus, also occurs in the upper part of the section, marking the SBZ 18/19 boundary. These events are associated with the phylogenetic development of the Nummulites fabianii and Heterostegina reticulata lineages. However, the calcareous plankton biostratigraphy indicates the section is well within the Priabonian; within planktonic foraminiferal Zones E14 and E15 and calcareous nannoplankton Zones CNE 18 and CNE 19. These results indicate larger foraminiferal events occur well above the planktonic foraminiferal extinction level and nannofossil assemblage changes indicating the events are not synchronous across groups, with implications for biostratigraphy and recognition of the basal Priabonian in different depositional settings and regions
Failure of JoAnne's Global Fit to the Wilson Coefficients in Rare B Decays: A Left-Right Model Example
In the Standard Model and many of its extensions, it is well known that all
of the observables associated with the rare decays and can be expressed in terms of the three Wilson coefficients,
, together with several universal kinematic
functions. In particular it has been shown that the numerical values of these
coefficients can be uniquely extracted by a three parameter global fit to data
obtainable at future -factories given sufficient integrated luminosity. In
this paper we examine if such global fits are also sensitive to new operators
beyond those which correspond to the above coefficients, i.e., whether is it
possible that new operators can be of sufficient importance for the three
parameter fit to fail and for this to be experimentally observable. Using the
Left-Right Symmetric Model as an example of a scenario with an extended
operator basis, we demonstrate via Monte Carlo techniques that such a
possibility can indeed be realized. In some sense this potential failure of the
global fit approach can actually be one of its greatest successes in
identifying the existence of new physics.Comment: 30 pages, 6 figure
The Impact of Flavour Changing Neutral Gauge Bosons on B->X_s gamma
The branching ratio of the rare decay B->X_s gamma provides potentially
strong constraints on models beyond the Standard Model. Considering a general
scenario with new heavy neutral gauge bosons, present in particular in Z' and
gauge flavour models, we point out two new contributions to the B->X_s gamma
decay. The first one originates from one-loop diagrams mediated by gauge bosons
and heavy exotic quarks with electric charge -1/3. The second contribution
stems from the QCD mixing of neutral current-current operators generated by
heavy neutral gauge bosons and the dipole operators responsible for the B->X_s
gamma decay. The latter mixing is calculated here for the first time. We
discuss general sum rules which have to be satisfied in any model of this type.
We emphasise that the neutral gauge bosons in question could also significantly
affect other fermion radiative decays as well as non-leptonic two-body B
decays, epsilon'/epsilon, anomalous (g-2)_mu and electric dipole moments.Comment: 31 pages, 5 figures; version published on JHEP; added magic QCD
numbers for flavour-violating Z gauge boson contribution to B -> X_s gamm
Unconstrained SU(2) Yang-Mills Quantum Mechanics with Theta Angle
The unconstrained classical system equivalent to spatially homogeneous SU(2)
Yang-Mills theory with theta angle is obtained and canonically quantized. The
Schr\"odinger eigenvalue problem is solved approximately for the low lying
states using variational calculation. The properties of the groundstate are
discussed, in particular its electric and magnetic properties, and the value of
the "gluon condensate" is calculated. Furthermore it is shown that the energy
spectrum of SU(2) Yang-Mills quantum mechanics is independent of the theta
angle. Explicit evaluation of the Witten formula for the topological
susceptibility gives strong support for the consistency of the variational
results obtained.Comment: 20 pages REVTEX, no figures, one reference added, final version to
appear in Phys. Rev.
Direct CP violation in radiative b decays in and beyond the Standard Model
We consider the partial rate asymmetry in the inclusive decay modes b to s
gamma and b to d gamma, concentrating on non-standard models with new charged
Higgs interactions. We find that the charged Higgs contribution to the
asymmetry for b to s gamma is small in such models due to a universal
cancellation mechanism. The asymmetry is therefore difficult to distinguish
experimentally from the Standard Model (SM) value, which is also small. The
cancellation mechanism is found to be rendered inoperative in supersymmetry due
to the presence of chargino loops. Unlike b to s gamma, the rate asymmetry for
b to d gamma in Higgs models can be quite different from its SM value,
generally ranging from -20% to +20%. Specific model calculations are performed
for the Three-Higgs Doublet Model and the ``Top'' Two-Higgs Doublet Model to
serve as illustrations. We also offer some suggestions that may be helpful to
experimentalists in the detection of the inclusive mode b to d gamma.Comment: RevTex, 24 pages, 6 figures, minor changes, version to appear in PR
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