92 research outputs found
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
Complete (O_7,O_8) contribution to B -> X_s gamma at order alpha_s^2
We calculate the set of O(alpha_s^2) corrections to the branching ratio and
to the photon energy spectrum of the decay process B -> X_s gamma originating
from the interference of diagrams involving the electromagnetic dipole operator
O_7 with diagrams involving the chromomagnetic dipole operator O_8. The
corrections evaluated here are one of the elements needed to complete the
calculations of the B -> X_s gamma branching ratio at next-to-next-to-leading
order in QCD. We conclude that this set of corrections does not change the
central value of the Standard Model prediction for Br(B -> X_s gamma) by more
than 1 %.Comment: 19 pages, 8 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
Complete NNLO QCD Analysis of B -> X_s l^+ l^- and Higher Order Electroweak Effects
We complete the next-to-next-to-leading order QCD calculation of the
branching ratio for B -> X_s l^+ l^- including recent results for the
three-loop anomalous dimension matrix and two-loop matrix elements. These new
contributions modify the branching ratio in the low-q^2 region, BR_ll, by about
+1% and -4%, respectively. We furthermore discuss the appropriate normalization
of the electromagnetic coupling alpha and calculate the dominant higher order
electroweak effects, showing that, due to accidental cancellations, they change
BR_ll by only -1.5% if alpha(mu) is normalized at mu = O(m_b), while they shift
it by about -8.5% if one uses a high scale normalization mu = O(M_W). The
position of the zero of the forward-backward asymmetry, q_0^2, is changed by
around +2%. After introducing a few additional improvements in order to reduce
the theoretical error, we perform a comprehensive study of the uncertainty. We
obtain BR_ll(1 GeV^2 <= q^2 <= 6 GeV^2) = (1.57 +- 0.16) x 10^-6 and q_0^2 =
(3.76 +- 0.33) GeV^2 and note that the part of the uncertainty due to the
b-quark mass can be easily reduced.Comment: 26 pages, 7 figures; v5: corrected normalisation in Eq. (5),
numerical results unchange
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
decays in the Left-Right Symmetric Model
We consider decays in the Left-Right Symmetric Model. Values
of observables sensitive to chiral structure such as the polarization
in the decays and the mixing-induced CP
asymmetries in the decays can deviate in the LRSM
significantly from the SM values. The combined analysis of and
as well as can be used to determine the
model parameters.Comment: 16 pages with 7 figures, Version to be published in PR
Stabilization of the Yang-Mills chaos in non-Abelian Born-Infeld theory
We investigate dynamics of the homogeneous time-dependent SU(2) Yang-Mills
fields governed by the non-Abelian Born-Infeld lagrangian which arises in
superstring theory as a result of summation of all orders in the string slope
parameter . It is shown that generically the Born-Infeld dynamics is
less chaotic than that in the ordinary Yang-Mills theory, and at high enough
field strength the Yang-Mills chaos is stabilized. More generally, a smothering
effect of the string non-locality on behavior of classical fields is
conjectured.Comment: 7 pages, 5 figure
The Benefits of B ---> K* l+ l- Decays at Low Recoil
Using the heavy quark effective theory framework put forward by Grinstein and
Pirjol we work out predictions for B -> K* l+ l-, l = (e, mu), decays for a
softly recoiling K*, i.e., for large dilepton masses sqrt{q^2} of the order of
the b-quark mass m_b. We work to lowest order in Lambda/Q, where Q = (m_b,
sqrt{q^2}) and include the next-to-leading order corrections from the charm
quark mass m_c and the strong coupling at O(m_c^2/Q^2, alpha_s). The leading
Lambda/m_b corrections are parametrically suppressed. The improved Isgur-Wise
form factor relations correlate the B -> K* l+ l- transversity amplitudes,
which simplifies the description of the various decay observables and provides
opportunities for the extraction of the electroweak short distance couplings.
We propose new angular observables which have very small hadronic
uncertainties. We exploit existing data on B -> K* l+ l- distributions and show
that the low recoil region provides powerful additional information to the
large recoil one. We find disjoint best-fit solutions, which include the
Standard Model, but also beyond-the-Standard Model ones. This ambiguity can be
accessed with future precision measurements.Comment: 31 pages, 8 figures; Instability near minimal recoil from numerics
removed, Fig. 1 replaced and minor shifts in short distance uncertainties in
SM predictions; typos corrected and references added; main results and
conclusions unchange
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