48 research outputs found
En-gauging Naturalness
The discovery of a 125.5 GeV Higgs with standard model-like couplings and
naturalness considerations motivate gauge extensions of the MSSM. We analyse
two variants of such an extension and carry out a phenomenological study of
regions of the parameter space satisfying current direct and indirect
constraints, employing state-of-the art two-loop RGE evolution and GMSB
boundary conditions. We find that due to the appearance of non-decoupled
D-terms it is possible to obtain a 125.5 GeV Higgs with stops below 2 TeV,
while the uncolored sparticles could still lie within reach of the LHC. We
compare the contributions of the stop sector and the non-decoupled D-terms to
the Higgs mass, and study their effect on the Higgs couplings. We further
investigate the nature of the next-to lightest supersymmetric particle, in
light of the GMSB motivated searches currently being pursued by ATLAS and CMS.Comment: 45 pages, 17 figures, Supplementary material
SupplementaryQSMxEW-Regime1.pdf attached in source. v2: preprint number added
v3: Appendix A.6, Published in EPJ
Threshold enhancement of diphoton resonances
The data collected by the LHC collaborations at an energy of 13 TeV indicates
the presence of an excess in the diphoton spectrum that would correspond to a
resonance of a 750 GeV mass. The apparently large production cross section is
nevertheless very difficult to explain in minimal models. We consider the
possibility that the resonance is a pseudoscalar boson with a two--photon
decay mediated by a charged and uncolored fermion having a mass at the threshold and a very small decay width, MeV; one can then generate
a large enhancement of the amplitude which explains the excess
without invoking a large multiplicity of particles propagating in the loop,
large electric charges and/or very strong Yukawa couplings. The implications of
such a threshold enhancement are discussed in two explicit scenarios: i) the
Minimal Supersymmetric Standard Model in which the state is produced via
the top quark mediated gluon fusion process and decays into photons
predominantly through loops of charginos with masses close to and
ii) a two Higgs doublet model in which is again produced by gluon fusion
but decays into photons through loops of vector--like charged heavy leptons. We
also comment on a minimal scenario in which the state couples only to
photons through a heavy lepton loop and is both produced and decays through
this coupling. In all these scenarios, while the mass of the charged fermion
has to be adjusted to be extremely close to half of the resonance mass, the
small total widths are naturally obtained if only suppressed three-body decay
channels occur. Finally, the implications of some of these scenarios for dark
matter are discussed.Comment: 15 pages, 4 figures, version submitted to journal with typos
correcte
B → K∗µ+µ− and Form Factors for Semi-Leptonic and Radiative B Decays
The hadronic environment of the LHC favours the study of exclusive modes, and of these semi-leptonic and radiative B decays will play a leading role in the search for new physics (NP). A prime example is the rare decay B→K∗(→ Kπ)µ+µ−, where the many measurable quantities offer important new tests of the Standard Model and its extensions. We define sets of CP-conserving and CP-violating observables which are studied in terms of the full form factors, calculated in QCD sum rules on the light-cone (LCSR), and QCD factorisation. Those with reduced dependence on hadronic quantities and sensitivity to NP are identified. In the first few years of data–taking at the LHC, the focus will be on quantities which are simple to extract while maximising the available NP sensitivity. Out of three
such observables, two are well known to the experimental community. However a third, one of the CP-conserving angular observables, leads to significant additional constraints on parameter space. We then study form factors for rare semi-leptonic and radiative B decays to K(∗) , ρ and φs mesons, combining theoretical and phenomenological constraints from Lattice QCD, LCSR, and dispersive bounds. We pay particular attention to form factor parameterisations which are based on the so-called series expansion, and study the related systematic uncertainties on a quantitative level. Finally we calculate the leading-twist O(αsβ0) corrections to the B → π transition form factor f+ (0) in LCSR, allowing an improved determination of the CKM matrix element |Vub |
Theoretical and Phenomenological Constraints on Form Factors for Radiative and Semi-Leptonic B-Meson Decays
We study transition form factors for radiative and rare semi-leptonic B-meson
decays into light pseudoscalar or vector mesons, combining theoretical
constraints and phenomenological information from Lattice QCD, light-cone sum
rules, and dispersive bounds. We pay particular attention to form factor
parameterisations which are based on the so-called series expansion, and study
the related systematic uncertainties on a quantitative level. In this context,
we also provide the NLO corrections to the correlation function between two
flavour-changing tensor currents, which enters the unitarity constraints for
the coefficients in the series expansion.Comment: 52 pages; v2: normalization error in (29ff.) corrected, conclusion
about relevance of unitarity bounds modified; form factor fits unaffected;
references added; v3: discussion on truncation of series expansion added,
matches version to be published in JHEP; v4: corrected typos in Tables 5 and
Symmetries and Asymmetries of B -> K* mu+ mu- Decays in the Standard Model and Beyond
The rare decay B -> K* (-> K pi) mu+ mu- is regarded as one of the crucial
channels for B physics as the polarization of the K* allows a precise angular
reconstruction resulting in many observables that offer new important tests of
the Standard Model and its extensions. These angular observables can be
expressed in terms of CP-conserving and CP-violating quantities which we study
in terms of the full form factors calculated from QCD sum rules on the
light-cone, including QCD factorization corrections. We investigate all
observables in the context of the Standard Model and various New Physics
models, in particular the Littlest Higgs model with T-parity and various MSSM
scenarios, identifying those observables with small to moderate dependence on
hadronic quantities and large impact of New Physics. One important result of
our studies is that new CP-violating phases will produce clean signals in
CP-violating asymmetries. We also identify a number of correlations between
various observables which will allow a clear distinction between different New
Physics scenarios.Comment: 56 pages, 18 figures, 14 tables. v5: Missing factor in eqs. (3.31-32)
and fig. 6 corrected. Minor misprints in eq. (2.10) and table A corrected.
Conclusions unchange
Two-loop Corrections to the B to pi Form Factor from QCD Sum Rules on the Light-Cone and |V(ub)|
We calculate the leading-twist O(alphas^2 beta0) corrections to the B to pi
transition form factor f+(0) in light-cone sum rules. We find that, as
expected, there is a cancellation between the O(alphas^2 beta0) corrections to
fB f+(0) and the large corresponding corrections to fB, calculated in QCD sum
rules. This suggests the insensitivity of the form factors calculated in the
light-cone sum rules approach to this source of radiative corrections. We
further obtain an improved determination of the CKM matrix element |V(ub)|,
using latest results from BaBar and Belle for f+(0)|V(ub)|.Comment: 18 pages, 3 figure
B →Vℓ+ℓ− in the Standard Model from light-cone sum rules
We present , , , and
form factors from light-cone sum rules (LCSR) at
for twist-2 and 3 and for
twist-4 with updated hadronic input parameters. Three asymptotic light-cone
distribution amplitudes of twist- (and ) are determined, necessary for
the form factors to obey the equations of motion. It is argued that the latter
constrain the uncertainty of tensor-to-vector form factor ratios thereby
improving the prediction of zeros of helicity amplitudes of major importance
for angular observables. We provide easy-to-use fits to the
LCSR results, including the full error correlation matrix, in all modes at low
as well as combined fits to LCSR and lattice results covering the entire
kinematic range for , and . The error
correlation matrix avoids the problem of overestimating the uncertainty in
phenomenological applications. Using the new form factors and recent
computations of non-factorisable contributions we provide Standard Model
predictions for as well as and
at low dilepton invariant mass. Employing our form factor results we extract the CKM element
from the semileptonic decays and
find good agreement with other exclusive determinations.Comment: 64 pages, 7 figures, 15 tables. v3: Minor clarifications, numerics
unchanged. Matches version published in JHE
COVID-19 in congenital heart disease (COaCHeD) study
Background: COVID-19 has caused significant worldwide morbidity and mortality. Congenital heart disease (CHD) is likely to increase vulnerability and understanding the predictors of adverse outcomes is key to optimising care.//
Objective: Ascertain the impact of COVID-19 on people with CHD and define risk factors for adverse outcomes.//
Methods: Multicentre UK study undertaken 1 March 2020–30 June 2021 during the COVID-19 pandemic. Data were collected on CHD diagnoses, clinical presentation and outcomes. Multivariable logistic regression with multiple imputation was performed to explore predictors of death and hospitalisation.//
Results: There were 405 reported cases (127 paediatric/278 adult). In children (age <16 years), there were 5 (3.9%) deaths. Adjusted ORs (AORs) for hospitalisation in children were significantly lower with each ascending year of age (OR 0.85, 95% CI 0.75 to 0.96 (p<0.01)). In adults, there were 24 (8.6%) deaths (19 with comorbidities) and 74 (26.6%) hospital admissions. AORs for death in adults were significantly increased with each year of age (OR 1.05, 95% CI 1.01 to 1.10 (p<0.01)) and with pulmonary arterial hypertension (PAH; OR 5.99, 95% CI 1.34 to 26.91 (p=0.02)). AORs for hospitalisation in adults were significantly higher with each additional year of age (OR 1.03, 95% CI 1.00 to 1.05 (p=0.04)), additional comorbidities (OR 3.23, 95% CI 1.31 to 7.97 (p=0.01)) and genetic disease (OR 2.87, 95% CI 1.04 to 7.94 (p=0.04)).//
Conclusions: Children were at low risk of death and hospitalisation secondary to COVID-19 even with severe CHD, but hospital admission rates were higher in younger children, independent of comorbidity. In adults, higher likelihood of death was associated with increasing age and PAH, and of hospitalisation with age, comorbidities and genetic disease. An individualised approach, based on age and comorbidities, should be taken to COVID-19 management in patients with CHD