A
bstract
We present a detailed analysis of QED corrections to
B
¯
→
K
¯
ℓ
+
ℓ
−
decays at the double-differential level. Cancellations of soft and collinear divergences are demonstrated analytically ...using the phase space slicing method. Whereas soft divergences are found to cancel at the differential level, the cancellation of the hard-collinear logs ln
m
ℓ
require, besides photon-inclusiveness, a specific choice of kinematic variables. In particular, hard-collinear logs in the lepton-pair invariant mass distribution (
q
2
), are sizeable and need to be treated with care when comparing with experiment. Virtual and real amplitudes are evaluated using an effective mesonic Lagrangian. Crucially, we show that going beyond this approximation does not introduce any further infrared sensitive terms. All analytic computations are performed for generic charges and are therefore adaptable to semileptonic decays such as
B
¯
→
D
ℓ
ν
¯
.
A
bstract
Motivated by additional experimental hints of Lepton Flavour Universality violation in
B
decays, both in charged- and in neutral-current processes, we analyse the ingredients necessary to ...provide a combined description of these phenomena. By means of an Effective Field Theory (EFT) approach, based on the hypothesis of New Physics coupled predominantly to the third generation of left-handed quarks and leptons, we show how this is possible. We demonstrate, in particular, how to solve the problems posed by electroweak precision tests and direct searches with a rather natural choice of model parameters, within the context of a U(2)
q
×U(2)
ℓ
flavour symmetry. We further exemplify the general EFT findings by means of simplified models with explicit mediators in the TeV range: coloured scalar or vector leptoquarks and colour-less vectors. Among these, the case of an SU(2)
L
-singlet vector leptoquark emerges as a particularly simple and successful framework.
The concept of zero dynamics of a nonlinear system was introduced about thirty years ago as nonlinear analogue of the concept of transmission zero of the transfer function of a system. This paper ...reviews a few historical landmarks in the development of this concept and then addresses some current challenging issues, such as the development of global and coordinate free version of a standard output-feedback design paradigm, the analysis of problems of stabilization and tracking in the presence of unstable zero dynamics, and extensions to multivariable systems.
A
bstract
Motivated by the recent LHCb announcement of a 3
.
1
σ
violation of lepton- flavor universality in the ratio
R
K
= Γ(
B
→
Kμ
+
μ
−
)
/
Γ(
B
→
Ke
+
e
−
), we present an updated, ...comprehensive analysis of the flavor anomalies seen in both neutral-current (
b
→
sℓ
+
ℓ
−
) and charged-current (
b
→
cτ
ν
¯
) decays of
B
mesons. Our study starts from a model-independent effective field-theory approach and then considers both a simplified model and a UV-complete extension of the Standard Model featuring a vector leptoquark
U
1
as the main mediator of the anomalies. We show that the new LHCb data corroborate the emerging pattern of a new, predominantly left-handed, semileptonic current-current interaction with a flavor structure respecting a (minimally) broken U(2)
5
flavor symmetry. New aspects of our analysis include a combined analysis of the semileptonic operators involving tau leptons, including in particular the important constraint from
B
s
-
B
¯
s
mixing, a systematic study of the effects of right-handed leptoquark couplings and of deviations from minimal flavor-symmetry breaking, a detailed analysis of various rare
B
-decay modes which would provide smoking-gun signatures of this non-standard framework (LFV decays, di-tau modes, and
B
→
K
(*)
ν
ν
¯
), and finally an updated analysis of collider bounds on the leptoquark mass and couplings.
Cushing's syndrome is a serious endocrine disease caused by chronic, autonomous, and excessive secretion of cortisol. The syndrome is associated with increased mortality and impaired quality of life ...because of the occurrence of comorbidities. These clinical complications include metabolic syndrome, consisting of systemic arterial hypertension, visceral obesity, impairment of glucose metabolism, and dyslipidaemia; musculoskeletal disorders, such as myopathy, osteoporosis, and skeletal fractures; neuropsychiatric disorders, such as impairment of cognitive function, depression, or mania; impairment of reproductive and sexual function; and dermatological manifestations, mainly represented by acne, hirsutism, and alopecia. Hypertension in patients with Cushing's syndrome has a multifactorial pathogenesis and contributes to the increased risk for myocardial infarction, cardiac failure, or stroke, which are the most common causes of death; risks of these outcomes are exacerbated by a prothrombotic diathesis and hypokalaemia. Neuropsychiatric disorders can be responsible for suicide. Immune disorders are common; immunosuppression during active disease causes susceptibility to infections, possibly complicated by sepsis, an important cause of death, whereas immune rebound after disease remission can exacerbate underlying autoimmune diseases. Prompt treatment of cortisol excess and specific treatments of comorbidities are crucial to prevent serious clinical complications and reduce the mortality associated with Cushing's syndrome.
A
bstract
In view of recent experimental indications of violations of Lepton Flavor Universality (LFU) in
B
decays, we analyze constraints and implications of LFU interactions, both using an ...effective theory approach, and an explicit dynamical model. We show that a simple dynamical model based on a SU(2)
L
triplet of massive vector bosons, coupled predominantly to third generation fermions (both quarks and leptons), can significantly improve the description of present data. In particular, the model decreases the tension between data and SM predictions concerning: i) the breaking of
τ
-
μ
universality in
B
→
D
(*)
ℓν
decays; ii) the breaking of
μ
-
e
universality in
B
→
Kℓ
+
ℓ
−
decays. Indirectly, the model might also decrease the discrepancy between exclusive and inclusive determinations of |
V
cb
| and |
V
ub
|. The minimal version of the model is in tension with ATLAS and CMS direct searches for the new massive vectors (decaying into
τ
+
τ
−
pairs), but this tension can be decreased with additional non-standard degrees of freedom. Further pre-dictions of the model both at low- and high-energies, in view of future high-statistics data, are discussed.
A
bstract
We analyze the stability of the Higgs sector of a three-site model with flavor-non-universal gauge interactions, whose spectrum of non-Standard-Model states spans three orders of magnitude. ...This model is inspired by deconstructing a five-dimensional theory where the generation index is in one-to-one relation to the position in the fifth dimension. It provides a good description of masses and mixing of the SM fermions in terms of scale hierarchies. We demonstrate that, within this construction, the mass term of the SM-like Higgs does not receive large corrections proportional to the highest mass scales. The model suffers only of the unavoidable “little hierarchy problem” between the electroweak scale and the lightest NP states, which are expected to be at the TeV scale.
A
bstract
We systematically explore ultraviolet complete models where flavour hierarchies emerge, via approximate accidental symmetries, from an underlying flavour non-universal gauge structure. In ...order to avoid large quantum corrections to the Higgs mass, the first layer of non-universality, separating the third generation from the light ones, should appear at the TeV scale. A handful of models survive the combined criteria of naturalness in the Higgs sector, having a semi-simple embedding in the UV, and compatibility with experiments. They all feature quark-lepton unification in the third family and a non-universal electroweak sector. We study in more detail the interesting option of having colour and hypercharge non-universal at the TeV scale, while SU(2)
L
remains universal up to high scales: this gauge structure turns to be very efficient in secluding the Higgs from large quantum corrections and predicting flavour mixing consistent with data. In all cases, these models imply a rich TeV-scale phenomenology within the reach of near-future direct and indirect experimental searches.
A
bstract
We present a thorough investigation of the vector leptoquark hypothesis for a combined explanation of the
B
-physics anomalies. We analyze this hypothesis from a twofold perspective, taking ...into account recent results from
B
-physics observables and high-
p
T
searches. First, using a simplified model, we determine the general conditions for a successful low-energy fit in presence of right-handed leptoquark couplings (neglected in previous analyses). Second, we show how these conditions, in particular a sizable 2-3 family mixing, can be achieved in a motivated ultraviolet completion. Our analysis reinforces the phenomenological success of the vector leptoquark hypothesis in addressing the anomalies, and its compatibility with motivated extensions of the Standard Model based on the idea of flavor non-universal gauge interactions. The implications of right-handed leptoquark couplings for a series of key low-energy observables, namely
B
s
→
ττ
and
τ
→
μ
lepton flavor violating processes, both in
τ
and in
B
decays, are discussed in detail. The role of the ultraviolet completion in precisely estimating other low-energy observables, most notably Δ
F
= 2 amplitudes, is also addressed.
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