1,799 research outputs found
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
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
Implications of large dimuon CP asymmetry in B_{d,s} decays on minimal flavor violation with low tan beta
The D0 collaboration has recently announced evidence for a dimuon CP
asymmetry in B_{d,s} decays of order one percent. If confirmed, this asymmetry
requires new physics. We argue that for minimally flavor violating (MFV) new
physics, and at low tan beta=v_u/v_d, there are only two four-quark operators
(Q_{2,3}) that can provide the required CP violating effect. The scale of such
new physics must lie below 260 GeV sqrt{tan beta}. The effect is universal in
the B_s and B_d systems, leading to S_{psi K}~sin(2beta)-0.15 and S_{psi
phi}~0.25. The effects on epsilon_K and on electric dipole moments are
negligible. The most plausible mechanism is tree-level scalar exchange. MFV
supersymmetry with low tan beta will be excluded. Finally, we explain how a
pattern of deviations from the Standard Model predictions for S_{psi phi},
S_{psi K} and epsilon_K can be used to test MFV and, if MFV holds, to probe its
structure in detail.Comment: 11 pages. v2: References adde
Constraining General Two Higgs Doublet Models by the Evolution of Yukawa Couplings
We study how general two Higgs doublet models can be constrained by
considering their properties under renormalization group evolution of the
Yukawa couplings. We take into account both the appearance of a Landau pole as
well as off-diagonal Yukawa couplings leading to flavour changing neutral
currents in violation with experimental constraints at the electroweak scale.
We find that the latter condition can be used to limit the amount of Z2
symmetry breaking allowed in a given model.Comment: 28 pages, 10 figures, added discussion of evolution from high to low
scales, to be published in JHE
Top mass dependent alpha_s^3 corrections to B-meson mixing in the MSSM
We compute the top mass dependent NLO strong interaction matching conditions
to the Delta F=2 effective Hamiltonian in the general MSSM. We study the
relevance of such corrections, comparing its size with that of previously known
NLO corrections in the limit mt->0, in scenarios with degeneracy, alignment,
and hierarchical squarks. We find that, while these corrections are generally
small, there are regions in the parameter space where the contributions to the
Wilson coefficients C1 and C4 could partially overcome the expected suppression
m_t/M_SUSY.Comment: 15 pages, 6 figure
CP Violation in Supersymmetry with Effective Minimal Flavour Violation
We analyze CP violation in supersymmetry with Effective Minimal Flavour
Violation, as recently proposed in arXiv:1011.0730. Unlike the case of standard
Minimal Flavour Violation, we show that all the phases allowed by the flavour
symmetry can be sizable without violating existing Electric Dipole Moment
constraints, thus solving the SUSY CP problem. The EDMs at one and two loops
are precisely analyzed as well as their correlations with the expected CP
asymmetries in B physics.Comment: 22 pages, 7 figures. v2: Discussion in section 2 extended,
conclusions unchanged. Matches published versio
A fourth generation, anomalous like-sign dimuon charge asymmetry and the LHC
A fourth chiral generation, with in the range GeV and a moderate value of the CP-violating phase can explain the
anomalous like-sign dimuon charge asymmetry observed recently by the D0
collaboration. The required parameters are found to be consistent with
constraints from other and decays. The presence of such quarks, apart
from being detectable in the early stages of the LHC, would also have important
consequences in the electroweak symmetry breaking sector.Comment: 18 pages, 9 figures, Figure 1 is modified, more discussions are added
in section 2. new references adde
Flavor Physics in an SO(10) Grand Unified Model
In supersymmetric grand-unified models, the lepton mixing matrix can possibly
affect flavor-changing transitions in the quark sector. We present a detailed
analysis of a model proposed by Chang, Masiero and Murayama, in which the
near-maximal atmospheric neutrino mixing angle governs large new b -> s
transitions. Relating the supersymmetric low-energy parameters to seven new
parameters of this SO(10) GUT model, we perform a correlated study of several
flavor-changing neutral current (FCNC) processes. We find the current bound on
B(tau -> mu gamma) more constraining than B(B -> X_s gamma). The LEP limit on
the lightest Higgs boson mass implies an important lower bound on tan beta,
which in turn limits the size of the new FCNC transitions. Remarkably, the
combined analysis does not rule out large effects in B_s-B_s-bar mixing and we
can easily accomodate the large CP phase in the B_s-B_s-bar system which has
recently been inferred from a global analysis of CDF and DO data. The model
predicts a particle spectrum which is different from the popular Constrained
Minimal Supersymmetric Standard Model (CMSSM). B(tau -> mu gamma) enforces
heavy masses, typically above 1 TeV, for the sfermions of the degenerate first
two generations. However, the ratio of the third-generation and
first-generation sfermion masses is smaller than in the CMSSM and a (dominantly
right-handed) stop with mass below 500 GeV is possible.Comment: 44 pages, 5 figures. Footnote and references added, minor changes,
Fig. 2 corrected; journal versio
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
S-layers at second glance? Altiarchaeal grappling hooks (hami) resemble archaeal S-layer proteins in structure and sequence
This is the final version of the article. Available from Frontiers Media via the DOI in this recordResearch on SM1-MSI was supported by the German Research Foundation (Deutsche Forschungsgemeinschaft), grant no. MO 1977/3-1 given to CM-E. AJP was supported by the German National Academic Foundation (Studienstiftung des deutschen Volkes)
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