3,234 research outputs found
New physics effects in the rare B_s --> \gamma \ell^+ \ell^- decays with polarized photon
Using the most general model independent form of the effective Hamiltonian,
the rare B_s --> \gamma \ell^+ \ell^- decays are studied by taking into account
the polarization of the photon. The total and the differential branching ratios
for these decays, when photon is in the positive and negative helicity states,
are presented. Dependence of these observables on the new Wilson coefficients
are studied. It is also investigated the sensitivity of "photon polarization
asymmetry" in B_s --> \gamma \ell^+ \ell^- decays to the new Wilson
coefficients. It has been shown that all these physical observables are very
sensitive to the existence of new physics beyond SM and their experimental
measurements can give valuable information about it.Comment: 17 pages, 14 figure
Double-Lepton Polarization Asymmetries and Branching Ratio of the B\rar \gamma l^+ l^- transition in Universal Extra Dimension
We study the radiative dileptonic B \rar \gamma l^+ l^- transition in the
presence of a universal extra dimension in the Applequist-Cheng-Dobrescu model.
In particular, using the corresponding form factors calculated via light cone
QCD sum rules, we analyze the branching ratio and double lepton polarization
asymmetries related to this channel and compare the results with the
predictions of the standard model. We show how the results deviate from
predictions of the standard model at lower values of the compactification
factor () of extra dimension.Comment: 20 Pages and 8 Figure
Heavy-to-Light Form Factors in the Final Hadron Large Energy Limit of QCD
We argue that the Large Energy Effective Theory (LEET), originally proposed
by Dugan and Grinstein, is applicable to exclusive semileptonic, radiative and
rare heavy-to-light transitions in the region where the energy release E is
large compared to the strong interaction scale and to the mass of the final
hadron, i.e. for q^2 not close to the zero-recoil point. We derive the
Effective Lagrangian from the QCD one, and show that in the limit of heavy mass
M for the initial hadron and large energy E for the final one, the heavy and
light quark fields behave as two-component spinors. Neglecting QCD
short-distance corrections, this implies that there are only three form factors
describing all the pseudoscalar to pseudoscalar or vector weak current matrix
elements. We argue that the dependence of these form factors with respect to M
and E should be factorizable, the M-dependence (sqrt(M)) being derived from the
usual heavy quark expansion while the E-dependence is controlled by the
behaviour of the light-cone distribution amplitude near the end-point u=1. The
usual expectation of the (1-u) behaviour leads to a 1/E^2 scaling law, that is
a dipole form in q^2. We also show explicitly that in the appropriate limit,
the Light-Cone Sum Rule method satisfies our general relations as well as the
scaling laws in M and E of the form factors, and obtain very compact and simple
expressions for the latter. Finally we note that this formalism gives
theoretical support to the quark model-inspired methods existing in the
literature.Comment: Latex2e, 25 pages, no figure. Slight changes in the title and the
phrasing. Misprint in Eq. (25) corrected. To appear in Phys. Rev.
Double-Lepton Polarization Asymmetries and Branching Ratio in B \rar K_{0}^{*}(1430) l^+ l^- transition from Universal Extra Dimension Model
We investigate the B \rar K_{0}^{*}(1430) l^+ l^- transition in the
Applequist-Cheng-Dobrescu model in the presence of a universal extra dimension.
In particular, we calculate double lepton polarization asymmetries and
branching ratio related to this channel and compare the obtained results with
the predictions of the standard model. Our analysis of the considered
observables in terms of radius of the compactified extra-dimension as the
new parameter of the model show a considerable discrepancy between the
predictions of two models in low values.Comment: 12 Pages, 15 Figures and 1 Tabl
Model Independent Analysis of the Forward-Backward Asymmetry for the Decay
The sensitivity of the zero position of the forward backward asymmetry
for the exclusive
decay is examined by using most general non-standard 4-fermion interactions.
Our analysis shows that the zero position of the forward backward asymmetry is
very sensitive to the sign and size of the Wilson coefficients corresponding to
the new vector type interactions, which are the counter partners of the usual
Standard Model operators but have opposite chirality. In addition to these, the
other significant effect comes from the interference of Scalar-Pseudoscalar and
Tensor type operators. These results will not only enhance our theoretical
understanding about the axial vector mesons but will also serve as a good tool
to look for physics beyond the SM.Comment: 14 pages, 8 figures, Published version that appears in EPJ
Study of Bs-> \phi l^+ l^-$ Decay in a Single Universal Extra Dimension
Utilizing form factors calculated within the light-cone sum rules, we have
evaluated the decay branching ratios of and in a single universal extra dimension model (UED), which is
viewed as one of the alternative theories beyond the standard model (SM). For
the decay , the dilepton invariant mass spectra, the
forward-backward asymmetry, and double lepton polarization are also calculated.
For each case, we compared the obtained results with predictions of the SM. In
lower values of the compactification factor 1/R, the only parameter in this
model, we see the considerable discrepancy between the UED and SM models.
However, when 1/R increases, the results of UED tend to diminish and at , two models have approximately the same predictions.
Compared with data from CDF of , the 1/R tends to be
larger than . We also note that the zero crossing point of
the forward-backward asymmetry is become smaller, which will be an important
plat to prob the contribution from the extra dimension model. The results
obtained in this work will be very useful in searching new physics beyond SM.
Moreover, the order of magnitude for branching ratios shows a possibility to
study these channels at the Large Hadron Collider (LHC), CDF and the future
super-B factory.Comment: 13 pages, 16 figure
Magnetization reversal in sub-100nm magnetic tunnel junctions with ultrathin MgO barrier biased along hard axis
We report on room temperature magnetoresistance and low frequency noise in
sub-100nm elliptic CoFeB/MgO/CoFeB magnetic tunnel junctions with ultrathin
(0.9nm) barriers. For magnetic fields applied along the hard axis, we observe
current induced magnetization switching between the antiparallel and parallel
alignments at DC current densities as low as 4*106A/cm2. We attribute the low
value of the critical current to the influence of localized reductions in the
tunnel barrier, which affects the current distribution. The analysis of random
telegraph noise, which appears in the field interval near a magnetization
switch, provides an estimate to the dimension of the pseudo pinholes that
trigger the magnetization switching via local spin torque. Micromagnetic
simulations qualitatively and quantitatively reproduce the main experimental
observations
New-physics contributions to the forward-backward asymmetry in B -> K* mu+ mu-
We study the forward-backward asymmetry (AFB) and the differential branching
ratio (DBR) in B -> K* mu+ mu- in the presence of new physics (NP) with
different Lorentz structures. We consider NP contributions from vector-axial
vector (VA), scalar-pseudoscalar (SP), and tensor (T) operators, as well as
their combinations. We calculate the effects of these new Lorentz structures in
the low-q^2 and high-q^2 regions, and explain their features through analytic
approximations. We find two mechanisms that can give a significant deviation
from the standard-model predictions, in the direction indicated by the recent
measurement of AFB by the Belle experiment. They involve the addition of the
following NP operators: (i) VA, or (ii) a combination of SP and T (slightly
better than T alone). These two mechanisms can be distinguished through
measurements of DBR in B -> K* mu+ mu- and AFB in B -> K mu+ mu-.Comment: 33 pages, revtex, 9 figures. Paper originally submitted with the
wrong figures. This is corrected in the replacement. An incorrect factor of 2
found in a formula. This is corrected and figures modified. Conclusions
unchanged. Typos correcte
Topologically Massive Gravity and Ricci-Cotton Flow
We consider Topologically Massive Gravity (TMG), which is three dimensional
general relativity with a cosmological constant and a gravitational
Chern-Simons term. When the cosmological constant is negative the theory has
two potential vacuum solutions: Anti-de Sitter space and Warped Anti-de Sitter
space. The theory also contains a massive graviton state which renders these
solutions unstable for certain values of the parameters and boundary
conditions. We study the decay of these solutions due to the condensation of
the massive graviton mode using Ricci-Cotton flow, which is the appropriate
generalization of Ricci flow to TMG. When the Chern-Simons coupling is small
the AdS solution flows to warped AdS by the condensation of the massive
graviton mode. When the coupling is large the situation is reversed, and warped
AdS flows to AdS. Minisuperspace models are constructed where these flows are
studied explicitly
Magnetic dipole moment of the (1232) from the reaction
The reaction in the -resonance
region is investigated as a method to access the magnetic
dipole moment. The calculations are performed within the context of an
effective Lagrangian model containing both the -resonant mechanism and
a background of non-resonant contributions to the
reaction. Results are shown both for existing and forthcoming experiments. In particular, the sensitivity of unpolarized
cross sections and photon asymmetries to the magnetic dipole moment
is displayed for those forthcoming data.Comment: 25 pages, 11 figure
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