1,300 research outputs found
On the Correlations between Flavour Observables in Minimal U(2)^3 Models
The stringent correlations between flavour observables in models with CMFV
are consistent with the present data except for the correlation Delta
M_{s,d}-epsilon_K. Motivated by the recent work of Barbieri et al, we compare
the CMFV correlations with the ones present in a special class of models with
an approximate global U(2)^3 flavour symmetry, constrained by a minimal set of
spurions governing the breakdown of this symmetry and the assumption that only
SM operators are relevant in flavour physics. This analog of CMFV to be called
MU(2)^3 allows to avoid the Delta M_{s,d}-epsilon_K tension in question because
of reduced flavour symmetry and implied non-MFV contributions to Delta M_{s,d}.
While the patterns of flavour violation in K meson system is the same as in
CMFV models, the CP-violation in B_{s,d} meson systems can deviate from the one
in the SM and CMFV models. We point out a stringent triple S_{psi K_S}-S_{psi
phi}-|V_ub| correlation in this class of models that could in the future
provide a transparent distinction between different MU(2)^3 models and in the
context of these models determine |V_ub| by means of precise measurements of
S_{psi K_S} and S_{psi phi} with only small hadronic uncertainties. For fixed
S_{psi K_S} the correlation between B(B^+ -> tau^+nu_tau) and S_{psi phi}
follows. We also find that MU(2)^3 models could in principle accommodate a
negative value of S_{psi phi}, provided |V_ub| is found to be in the ballpark
of exclusive determinations and the particular MU(2)^3 model provides a 25%
enhancement of epsilon_K. A supersymmetric U(2)^3 model worked out in the
Barbieri-School appears to satisfy these requirements. However if B(B^+ ->
tau^+nu_tau)>1.0 10^{-4} will be confirmed by future experiments only positive
S_{psi phi} is allowed in this framework. We summarize briefly the pattern of
flavour violation in rare K and B_{s,d} decays in MU(2)^3 models.Comment: 28 pages, 6 figures; v2: Few references and discussion on CP
violation in B_s-> mu^+ mu^- added; v3: Several clarifying comments added,
conclusions unchanged, version accepted for publication in JHE
Waiting for Clear Signals of New Physics in B and K Decays
We classify the extensions of the Standard Model (SM) according to the
structure of local operators in the weak effective Hamiltonian and the presence
or absence of new flavour and CP-violating interactions beyond those
represented by the CKM matrix. In particular we review characteristic
properties of models with minimal flavour violation (MFV), models with
significant contributions from Higgs penguins and models with enhanced Z^0
penguins carrying a large new CP-violating phase. Within the latter models, the
anomalous behaviour of certain B\to\pi K observables implies large departures
from the SM predictions for rare and CP-violating K and B decays. Most
spectacular is the enhancement of Br(K_L->pi^0 nu nubar) by one order of
magnitude and a strong violation of the MFV relation
(\sin2\beta)_{\pi\nu\bar\nu}=(\sin2\beta)_{\psi K_S}. On the other hand our
prediction for (\sin2\beta)_{\phi K_S}\approx 0.9 differs from the Belle result
by the sign but is consistent with the BaBar value. We give a personal shopping
list for the coming years.Comment: Main latex-file, 4 figures, 22 page
Two-Dimensional Hydrodynamic Core-Collapse Supernova Simulations with Spectral Neutrino Transport II. Models for Different Progenitor Stars
1D and 2D supernova simulations for stars between 11 and 25 solar masses are
presented, making use of the Prometheus/Vertex neutrino-hydrodynamics code,
which employs a full spectral treatment of the neutrino transport.
Multi-dimensional transport aspects are treated by the ``ray-by-ray plus''
approximation described in Paper I. Our set of models includes a 2D calculation
for a 15 solar mass star whose iron core is assumed to rotate rigidly with an
angular frequency of 0.5 rad/s before collapse. No important differences were
found depending on whether random seed perturbations for triggering convection
are included already during core collapse, or whether they are imposed on a 1D
collapse model shortly after bounce. Convection below the neutrinosphere sets
in about 40 ms p.b. at a density above 10**12 g/cm^3 in all 2D models, and
encompasses a layer of growing mass as time goes on. It leads to a more
extended proto-neutron star structure with accelerated lepton number and energy
loss and significantly higher muon and tau neutrino luminosities, but reduced
mean energies of the radiated neutrinos, at times later than ~100 ms p.b. In
case of an 11.2 solar mass star we find that low (l = 1,2) convective modes
cause a probably rather weak explosion by the convectively supported
neutrino-heating mechanism after ~150 ms p.b. when the 2D simulation is
performed with a full 180 degree grid, whereas the same simulation with 90
degree wedge fails to explode like all other models. This sensitivity
demonstrates the proximity of our 2D models to the borderline between success
and failure, and stresses the need of simulations in 3D, ultimately without the
axis singularity of a polar grid. (abridged)Comment: 42 pages, 44 figures; revised according to referee comments; accepted
to Astronomy & Astrophysic
Core Collapse and Then? The Route to Massive Star Explosions
The rapidly growing base of observational data for supernova explosions of
massive stars demands theoretical explanations. Central of these is a
self-consistent model for the physical mechanism that provides the energy to
start and drive the disruption of the star. We give arguments why the delayed
neutrino-heating mechanism should still be regarded as the standard paradigm to
explain most explosions of massive stars and show how large-scale and even
global asymmetries can result as a natural consequence of convective overturn
in the neutrino-heating region behind the supernova shock. Since the explosion
is a threshold phenomenon and depends sensitively on the efficiency of the
energy transfer by neutrinos, even relatively minor differences in numerical
simulations can matter on the secular timescale of the delayed mechanism. To
enhance this point, we present some results of recent one- and two-dimensional
computations, which we have performed with a Boltzmann solver for the neutrino
transport and a state-of-the-art description of neutrino-matter interactions.
Although our most complete models fail to explode, the simulations demonstrate
that one is encouragingly close to the critical threshold because a modest
variation of the neutrino transport in combination with postshock convection
leads to a weak neutrino-driven explosion with properties that fulfill
important requirements from observations.Comment: 14 pages; 3 figures. Invited Review, in: ``From Twilight to
Highlight: The Physics of Supernovae'', Eds. W. Hillebrandt and B.
Leibundgut, Springer Series ``ESO Astrophysics Symposia'', Berli
Effects of R-parity violation on direct CP violation in B decays and extraction of
In the standard model, direct CP-violating asymmetries for are roughly 2% based on perturbative calculation. Rescattering effects might
enhance it to at most (20-25)%. We show that lepton-number-violating couplings
in supersymmetric models without R-parity are capable of inducing as large as
100% CP asymmetry in this channel. Such effects drastically modify the allowed
range of the CKM parameter arising from the combinations of the
observed charged and neutral B decays in the modes. With a multichannel
analysis in B decays, one can either discover this exciting new physics, or
significantly improve the existing constraints on it.Comment: Latex, 5 pages; minor changes, to appear in Phys Rev Let
Penguin decays of B mesons
Penguin, or loop, decays of B mesons induce effective flavor-changing neutral
currents, which are forbidden at tree level in the Standard Model. These decays
give special insight into the CKM matrix and are sensitive to non-standard
model effects. In this review, we give a historical and theoretical
introduction to penguins and a description of the various types of penguin
processes: electromagnetic, electroweak, and gluonic. We review the
experimental searches for penguin decays, including the measurements of the
electromagnetic penguins b -> s gamma and B -> K* gamma and gluonic penguins B
-> K pi, B+ -> omega K+ and B -> eta' K, and their implications for the
Standard Model and New Physics. We conclude by exploring the future prospects
for penguin physics.Comment: 49 pages, LATEX, 30 embedded figures, submitted to Annual Reviews of
Nuclear and Particle Scienc
An upper bound on the Kaon B-parameter and Re(epsilon_K)
New precise data in B physics and theoretical developments in K physics lead
us to reconsider the weak K^0-\bar{K}^0 transition from a large-N_c viewpoint,
N_c being the number of colors. In this framework, we infer an upper limit on
\hat{B}_K and the Kaon indirect CP violation.Comment: 11 pages, 4 figures. V2 : Minor corrections, final version accepted
for publication in JHE
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
Rare K and B Decays in a Warped Extra Dimension with Custodial Protection
We present a complete study of rare K and B meson decays in a warped extra
dimensional model with a custodial protection of (both diagonal and
non-diagonal) Z d_L^i \bar d_L^j couplings, including K^+ -> pi^+ nu anti-nu,
K_L -> pi^0 nu anti-nu, K_L -> pi^0 l^+ l^-, K_L -> mu^+ mu^-, B_{s,d} -> mu^+
mu^-, B -> K nu anti-nu, B -> K^* nu anti-nu and B -> X_{s,d} nu anti-nu. In
this model in addition to Standard Model one loop contributions these processes
receive tree level contributions from the Z boson and the new heavy electroweak
gauge bosons. We analyse all these contributions that turn out to be dominated
by tree level Z boson exchanges governed by right-handed couplings to down-type
quarks. Imposing all existing constraints from Delta F=2 transitions analysed
by us recently and fitting all quark masses and CKM mixing parameters we find
that a number of branching ratios for rare K decays can differ significantly
from the SM predictions, while the corresponding effects in rare B decays are
modest, dominantly due to the custodial protection being more effective in B
decays than in K decays. In order to reduce the parameter dependence we study
correlations between various observables within the K system, within the B
system and in particular between K and B systems, and also between Delta F=2
and Delta F=1 observables. These correlations allow for a clear distinction
between this new physics scenario and models with minimal flavour violation or
the Littlest Higgs Model with T-parity, and could give an opportunity to future
experiments to confirm or rule out the model. We show how our results would
change if the custodial protection of Z d_L^i bar d^j_L couplings was absent.
In the case of rare B decays the modifications are spectacular.Comment: 50 pages, 17 figures. v2: minor clarifying comments and references
added. v3: few clarifying comments added, matches published versio
The effects of non-standard Z couplings on the lepton polarizations in B_s to \gamma \ell^+ \ell^- decays
The fact that the measured B to \pi \pi, \pi K branching ratios exhibit
puzzling patterns has received a lot of attention in the literature and
motivated the formulation of a series of new physics scenarios with enhanced
Z-penguins. In this work, we analyze the effect of such an enhancement on the
lepton polarization asymmetries of B_s to \gamma \ell^+ \ell^- decays by
applying the results of a specific scenario for the solution of ``B to \pi K
puzzle''.Comment: 12 pages, 6 figure
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