776 research outputs found
Minimal Flavour Violation for Leptoquarks
Scalar leptoquarks, with baryon and lepton number conserving interactions,
could have TeV scale masses, and be produced at colliders or contribute to a
wide variety of rare decays. In pursuit of some insight as to the most
sensitive search channels, We assume that the leptoquark-lepton-quark coupling
can be constructed from the known mass matrices. We estimate the rates for
selected rare processes in three cases: leptoquarks carrying lepton and quark
flavour, leptoquarks with quark flavour only, and unflavoured leptoquarks. We
find that leptoquark decay to top quarks is an interesting search channel.Comment: 17 pages, 2 figures, minor changes and references adde
Composite Leptoquarks at the LHC
If electroweak symmetry breaking arises via strongly-coupled physics, the
observed suppression of flavour-changing processes suggests that fermion masses
should arise via mixing of elementary fermions with composite fermions of the
strong sector. The strong sector then carries colour charge, and may contain
composite leptoquark states, arising either as TeV scale resonances, or even as
light, pseudo-Nambu-Goldstone bosons. The latter, since they are coupled to
colour, get a mass of the order of several hundred GeV, beyond the reach of
current searches at the Tevatron. The same generic mechanism that suppresses
flavour-changing processes suppresses leptoquark-mediated rare processes,
making it conceivable that the many stringent constraints may be evaded. The
leptoquarks couple predominantly to third-generation quarks and leptons, and
the prospects for discovery at LHC appear to be good. As an illustration, a
model based on the Pati-Salam symmetry is described, and its embedding in
models with a larger symmetry incorporating unification of gauge couplings,
which provide additional motivation for leptoquark states at or below the TeV
scale, is discussed.Comment: 10 pp, version to appear in JHE
LHC sensitivity to lepton flavour violating Z boson decays
We estimate that the LHC could set bounds BR(Z -> mu^\pm e^\mp) < 4.1 *
10^{-7} and BR(Z -> tau^\pm mu^\mp)< 3.5 * 10^{-6} (at 95% C.L.) with 20
inverse fb of data at 8 TeV. A similar sensitivity can be anticipated for Z ->
tau^\pm e^\mp, because we consider leptonic tau decays such that Z -> tau^+
mu^- gives e^+ \mu^- +$ invisibles. These limits can be compared to the LEP1
bounds of order 10^{-5} to 10^{-6}. Such collider searches are sensitive to a
flavour-changing effective Z coupling which is energy dependent, so are
complementary to bounds obtained from tau to 3mu and mu to 3e.Comment: 11 pages, 2 figures, version for publicatio
Flavourful Production at Hadron Colliders
We ask what new states may lie at or below the TeV scale, with sizable
flavour-dependent couplings to light quarks, putting them within reach of
hadron colliders via resonant production, or in association with Standard Model
states. In particular, we focus on the compatibility of such states with
stringent flavour-changing neutral current and electric-dipole moment
constraints. We argue that the broadest and most theoretically plausible
flavour structure of the new couplings is that they are hierarchical, as are
Standard Model Yukawa couplings, although the hierarchical pattern may well be
different. We point out that, without the need for any more elaborate or
restrictive structure, new scalars with "diquark" couplings to standard quarks
are particularly immune to existing constraints, and that such scalars may
arise within a variety of theoretical paradigms. In particular, there can be
substantial couplings to a pair of light quarks or to one light and one heavy
quark. For example, the latter possibility may provide a flavour-safe
interpretation of the asymmetry in top quark production observed at the
Tevatron. We thereby motivate searches for diquark scalars at the Tevatron and
LHC, and argue that their discovery represents one of our best chances for new
insight into the Flavour Puzzle of the Standard Model.Comment: 18 pp., 8 figures, references adde
Gauged Flavor Group with Left-Right Symmetry
We construct an anomaly-free extension of the left-right symmetric model,
where the maximal flavor group is gauged and anomaly cancellation is guaranteed
by adding new vectorlike fermion states. We address the question of the lowest
allowed flavor symmetry scale consistent with data. Because of the mechanism
recently pointed out by Grinstein et al. tree-level flavor changing neutral
currents turn out to play a very weak constraining role. The same occurs, in
our model, for electroweak precision observables. The main constraint turns out
to come from WR-mediated flavor changing neutral current box diagrams,
primarily K - Kbar mixing. In the case where discrete parity symmetry is
present at the TeV scale, this constraint implies lower bounds on the mass of
vectorlike fermions and flavor bosons of 5 and 10 TeV respectively. However,
these limits are weakened under the condition that only SU(2)_R x U(1)_{B-L} is
restored at the TeV scale, but not parity. For example, assuming the SU(2)
gauge couplings in the ratio gR/gL approx 0.7 allows the above limits to go
down by half for both vectorlike fermions and flavor bosons. Our model provides
a framework for accommodating neutrino masses and, in the parity symmetric
case, provides a solution to the strong CP problem. The bound on the lepton
flavor gauging scale is somewhat stronger, because of Big Bang Nucleosynthesis
constraints. We argue, however, that the applicability of these constraints
depends on the mechanism at work for the generation of neutrino masses.Comment: 1+23 pages, 1 table, 5 figures. v3: some more textual fixes (main
change: discussion of Lepton Flavor Violating observables rephrased). Matches
journal versio
Flavor Violating Higgs Decays
We study a class of nonstandard interactions of the newly discovered 125 GeV
Higgs-like resonance that are especially interesting probes of new physics:
flavor violating Higgs couplings to leptons and quarks. These interaction can
arise in many frameworks of new physics at the electroweak scale such as two
Higgs doublet models, extra dimensions, or models of compositeness. We rederive
constraints on flavor violating Higgs couplings using data on rare decays,
electric and magnetic dipole moments, and meson oscillations. We confirm that
flavor violating Higgs boson decays to leptons can be sizeable with, e.g., h ->
tau mu and h -> tau e branching ratios of order 10% perfectly allowed by low
energy constraints. We estimate the current LHC limits on h -> tau mu and h ->
tau e decays by recasting existing searches for the SM Higgs in the tau-tau
channel and find that these bounds are already stronger than those from rare
tau decays. We also show that these limits can be improved significantly with
dedicated searches and we outline a possible search strategy. Flavor violating
Higgs decays therefore present an opportunity for discovery of new physics
which in some cases may be easier to access experimentally than flavor
conserving deviations from the Standard Model Higgs framework.Comment: 39 pages, 12 figures, 3 tables; v2: Improved referencing, updated mu
-> 3e bounds to include large loop contributions, corrected single top
constraints; conclusions unchanged; matches version to be published in JHEP;
v3: included 2-loop contributions in mu -> e conversion, improved discussion
of tau -> 3 mu and of EDM constraints on FV top-Higgs couplings; conclusions
unchange
Evidence-based practice educational intervention studies: A systematic review of what is taught and how it is measured
Abstract Background Despite the established interest in evidence-based practice (EBP) as a core competence for clinicians, evidence for how best to teach and evaluate EBP remains weak. We sought to systematically assess coverage of the five EBP steps, review the outcome domains measured, and assess the properties of the instruments used in studies evaluating EBP educational interventions. Methods We conducted a systematic review of controlled studies (i.e. studies with a separate control group) which had investigated the effect of EBP educational interventions. We used citation analysis technique and tracked the forward and backward citations of the index articles (i.e. the systematic reviews and primary studies included in an overview of the effect of EBP teaching) using Web of Science until May 2017. We extracted information on intervention content (grouped into the five EBP steps), and the outcome domains assessed. We also searched the literature for published reliability and validity data of the EBP instruments used. Results Of 1831 records identified, 302 full-text articles were screened, and 85 included. Of these, 46 (54%) studies were randomised trials, 51 (60%) included postgraduate level participants, and 63 (75%) taught medical professionals. EBP Step 3 (critical appraisal) was the most frequently taught step (63 studies; 74%). Only 10 (12%) of the studies taught content which addressed all five EBP steps. Of the 85 studies, 52 (61%) evaluated EBP skills, 39 (46%) knowledge, 35 (41%) attitudes, 19 (22%) behaviours, 15 (18%) self-efficacy, and 7 (8%) measured reactions to EBP teaching delivery. Of the 24 instruments used in the included studies, 6 were high-quality (achieved ≥3 types of established validity evidence) and these were used in 14 (29%) of the 52 studies that measured EBP skills; 14 (41%) of the 39 studies that measured EBP knowledge; and 8 (26%) of the 35 studies that measured EBP attitude. Conclusions Most EBP educational interventions which have been evaluated in controlled studies focus on teaching only some of the EBP steps (predominantly critically appraisal of evidence) and did not use high-quality instruments to measure outcomes. Educational packages and instruments which address all EBP steps are needed to improve EBP teaching
Higgs-mediated FCNCs: Natural Flavour Conservation vs. Minimal Flavour Violation
We compare the effectiveness of two hypotheses, Natural Flavour Conservation
(NFC) and Minimal Flavour Violation (MFV), in suppressing the strength of
flavour-changing neutral-currents (FCNCs) in models with more than one Higgs
doublet. We show that the MFV hypothesis, in its general formulation, is more
stable in suppressing FCNCs than the hypothesis of NFC alone when quantum
corrections are taken into account. The phenomenological implications of the
two scenarios are discussed analysing meson-antimeson mixing observables and
the rare decays B -> mu+ mu-. We demonstrate that, introducing flavour-blind CP
phases, two-Higgs doublet models respecting the MFV hypothesis can accommodate
a large CP-violating phase in Bs mixing, as hinted by CDF and D0 data and,
without extra free parameters, soften significantly in a correlated manner the
observed anomaly in the relation between epsilon_K and S_psi_K.Comment: 27 pages, 4 figures. v3: minor modifications (typos corrected and few
refs. added), conclusions unchanged; 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
Neutrino masses from new generations
We reconsider the possibility that Majorana masses for the three known
neutrinos are generated radiatively by the presence of a fourth generation and
one right-handed neutrino with Yukawa couplings and a Majorana mass term. We
find that the observed light neutrino mass hierarchy is not compatible with low
energy universality bounds in this minimal scenario, but all present data can
be accommodated with five generations and two right-handed neutrinos. Within
this framework, we explore the parameter space regions which are currently
allowed and could lead to observable effects in neutrinoless double beta decay,
conversion in nuclei and experiments. We
also discuss the detection prospects at LHC.Comment: 28 pages, 4 figures. Version to be published. Some typos corrected.
Improved figures 3 and
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