102 research outputs found
Predictions for decays
We present a phenomenological study of the rare double radiative decay in the Standard Model (SM) and beyond. Using the operator
product expansion (OPE) technique, we estimate the short-distance (SD)
contribution to the decay amplitude in a region of the phase space which is
around the point where all decay products have energy in the rest
frame of the -meson. At lowest order in 1/Q, where is of order ,
the matrix element is then expressed in terms of the
usual form factors known from semileptonic rare decays. The integrated
SD branching ratio in the SM in the OPE region turns out to be . We work
out the di-photon invariant mass distribution with and without the resonant
background through . In the SM,
the resonance contribution is dominant in the region of phase space where the
OPE is valid. The present experimental upper limit on
decays, which constrains the scalar/pseudoscalar Four-Fermi operators with
, leaves considerable room for new physics in the
one-particle-irreducible contribution to decays. In this
case, we find that the SD branching ratio can be
enhanced by one order of magnitude with respect to its SM value and the SD
contribution can lie outside of the resonance peaks.Comment: 17 pages, 4 figures; Note added on Schouten identity and 2 references
added; v4: typos in Eqs (8), (44) and erroneous statement on mixing before Eq
(44) fixed. All results and conclusions unchange
Can there be any new physics in b -> d penguins
We analyze the possibility of observing new physics effects in the
penguin amplitudes. For this purpose, we consider the decay mode , which has only penguin contributions. Using the QCD
factorization approach, we find very tiny CP violating effects in the standard
model for this process. Furthermore, we show that the minimal supersymmetric
standard model with mass insertion and R-parity violating supersymmetric
model can provide substantial CP violation effects. Observation of sizable CP
violation in this mode would be a clear signal of new physics.Comment: Published versio
A general analysis with trilinear and bilinear R-parity violating couplings in the light of recent SNO data
We analyse an extension of the minimal supersymmetric standard model
including the dominant trilinear and bilinear R-parity violating contributions.
We take the trilinear terms from the superpotential and the bilinear terms from
the superpotential as well as the scalar potential. We compute the neutrino
masses induced by those couplings and determine the allowed ranges of the
R-parity violating parameters that are consistent with the latest SNO results,
atmospheric data and the Chooz constraint. We also estimate the effective mass
for neutrinoless double beta decay in such scenarios.Comment: 7 pages, Revtex, 1 PS figur
Reexamining nonstandard interaction effects on supernova neutrino flavor oscillations
Several extensions of the standard electroweak model allow new four-fermion
interactions (nu_a nu_b * ff) with strength eps_ab*G_F, where (a,b) are flavor
indices. We revisit their effects on flavor oscillations of massive
(anti)neutrinos in supernovae, in order to achieve, in the region above the
protoneutron star, an analytical treatment valid for generic values of the
neutrino mixing angles (omega,phi,psi)=(theta_12,theta_13,theta_23). Assuming
that eps_ab<<1, we find that the leading effects on the flavor transitions
occurring at high (H) and low (L) density along the supernova matter profile
can be simply embedded through the replacements phi-->phi+eps_H and
omega-->omega+eps_L, respectively, where eps_H and eps_L are specific linear
combinations of the eps_ab's. Similar replacements hold for eventual
oscillations in the Earth matter. From a phenomenological point of view, the
most relevant consequence is a possible uncontrolled bias (phi-->phi+eps_H) in
the value of the mixing angle phi inferred by inversion of supernova neutrino
data. Such a drawback, however, does not preclude the discrimination of the
neutrino mass spectrum hierarchy (direct or inverse) through supernova neutrino
oscillations.Comment: Text clarified, one figure added. To appear in PR
Effects of new physics in neutrino oscillations in matter
A new flavor changing electron neutrino interaction with matter would always
dominate the nu_e oscillation probability at sufficiently high neutrino
energies. Being suppressed by theta_{13}, the energy scale at which the new
effect starts to be relevant may be within the reach of realistic experiments,
where the peculiar dependence of the signal with energy could give rise to a
clear signature in the nu_e --> nu_tau channel. The latter could be observed by
means of a coarse large magnetized detector by exploiting tau --> mu decays. We
discuss the possibility of identifying or constraining such effects with a high
energy neutrino factory. We also comment on the model independent limits on
them.Comment: 11 pages, 5 figure
B --> Phi K_S and Supersymmetry
The rare decay B --> Phi K_S is a well-known probe of physics beyond the
Standard Model because it arises only through loop effects yet has the same
time-dependent CP asymmetry as B --> Psi K_S. Motivated by recent data
suggesting new physics in B --> Phi K_S, we look to supersymmetry for possible
explanations, including contributions mediated by gluino loops and by Higgs
bosons. Chirality-preserving LL and RR gluino contributions are generically
small, unless gluinos and squarks masses are close to the current lower bounds.
Higgs contributions are also too small to explain a large asymmetry if we
impose the current upper limit on B(B_s --> mu mu). On the other hand,
chirality-flipping LR and RL gluino contributions can provide sizable effects
and while remaining consistent with related results in B --> Psi K_S, Delta
M_s, B --> X_s gamma and other processes. We discuss how the LR and RL
insertions can be distinguished using other observables, and we provide a
string-based model and other estimates to show that the needed sizes of mass
insertions are reasonable.Comment: 33 pages, 32 figures, Updated version for PRD. Includes discussions
of other recent works on this topic. Added discussions & plots for gluino
mass dependence and effects of theoretical uncertaintie
Atmospheric Neutrinos Can Make Beauty Strange
The large observed mixing angle in atmospheric neutrinos, coupled with Grand
Unification, motivates the search for a large mixing between right-handed
strange and bottom squarks. Such mixing does not appear in the standard CKM
phenomenology, but may induce significant b to s transitions through gluino
diagrams. Working in the mass eigenbasis, we show quantitatively that an order
one effect on CP violation in B_d to phi+K_S is possible due to a large mixing
between right-handed b and s squarks, while still satisfying constraints from b
to s + gamma. We also include the effect of right- and left-handed bottom
squark mixing proportional to m_b*mu*tan(beta). For small mu*tan(beta) there
may also be a large effect in B_s mixing correlated with a large effect in B_d
to phi+K_S, typically mixing effects are greater than 100 ps^{-1}, an
unambiguous signal of new physics at Tevatron Run II.Comment: 32 pages, LaTeX. Corrected a factor of two mistake in the code; the
possible impact on B -> phi K_s became larger. Figures and discussion
updated, a reference adde
Can lepton flavor violating interactions explain the LSND results?
If the atmospheric and the solar neutrino problem are both explained by
neutrino oscillations, and if there are only three light neutrinos, then all
mass-squared differences between the neutrinos are known. In such a case,
existing terrestrial neutrino oscillation experiments cannot be significantly
affected by neutrino oscillations, but, in principle there could be an anomaly
in the neutrino flux due to new neutrino interactions. We discuss how a
non-standard muon decay would modify the
neutrino production processes of these experiments. Since violation
is small for New Physics above the weak scale one can use related
flavor-violating charged lepton processes to constrain these decays in a model
independent way. We show that the upper bounds on ,
muonium-antimuonium conversion and rule out any observable
effect for the present experiments due to
for , respectively. Applying similar arguments to
flavor-changing semi-leptonic reactions we exclude the possibility that the
"oscillation signals" observed at LSND are due to flavor-changing interactions
that conserve total lepton number.Comment: 21 pages, 6 figures, Latex; minor correction
Chargino Contributions in Asymmetry
CP asymmetry in decay is studied in a special context of
supersymmetry theories, in which the charginos play an important role. We find
that in addition to the gluino, chargino can also make large contributions to
CP asymmetry in decay. After considering the constraints from
decay, we study three special scenarios: (a). Large mixing on
left-handed charm and top squarks (LL mixing); (b). Large mixing on
right-handed charm and top squarks (RR mixing); (c). Large mixing on
left-handed charm and top squarks plus right-handed charm and top squarks (LL +
RR mixing). We show quantitatively that because of large squark mixing within
second and third generations, an (1) effect on CP violation in is possible
Atmospheric Neutrino Oscillations and New Physics
We study the robustness of the determination of the neutrino masses and
mixing from the analysis of atmospheric and K2K data under the presence of
different forms of phenomenologically allowed new physics in the nu_mu--nu_tau
sector. We focus on vector and tensor-like new physics interactions which allow
us to treat, in a model independent way, effects due to the violation of the
equivalence principle, violations of the Lorentz invariance both CPT conserving
and CPT violating, non-universal couplings to a torsion field and non-standard
neutrino interactions with matter. We perform a global analysis of the full
atmospheric data from SKI together with long baseline K2K data in the presence
of nu_mu -> nu_tau transitions driven by neutrino masses and mixing together
with sub-dominant effects due to these forms of new physics. We show that
within the present degree of experimental precision, the extracted values of
masses and mixing are robust under those effects and we derive the upper bounds
on the possible strength of these new interactions in the nu_mu--nu_tau sector.Comment: 22 pages, LaTeX file using RevTEX4, 5 figures and 4 tables include
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