arXiv subjects

Francesco Sannino

Publications and source records attributed to Francesco Sannino.

At least 109 records · Page 6Linked to original sources

arXiv2019

Flavour anomalies after the $R_{K^*}$ measurement

The LHCb measurement of the $μ/e$ ratio $R_{K^*}$ indicates a deficit with respect to the Standard Model prediction, supporting earlier hints of lepton universality violation observed in the $R_K$ ratio. We show that the $R_K$ and $R_{K^*}$ ratios alone constrain the chiralities of the states contributing to these anomalies, and we find deviations from the Standard Model at the $4σ$ level. This conclusion is further corroborated by hints in the theoretically challenging $b\to sμ^+μ^-$ distributions. Theoretical interpretations in terms of $Z'$, lepto-quarks, loop mediators, and composite dynamics are discussed. We highlight their distinctive features in terms of chiralities and flavour structure relevant for the observed anomalies.

hep-ph↗

arXiv2019

Dual RG flows in 4D

We present a prescription for using the a central charge to determine the flow of a strongly coupled supersymmetric theory from its weakly coupled dual. The approach is based on the equivalence of the scale-dependent a-parameter derived from the four-dilaton amplitude with the a-parameter determined from the Lagrange multiplier method with scale-dependent R-charges. We explicitly demonstrate this equivalence for massive free N=1 superfields and for weakly coupled SQCD.

hep-th↗

arXiv2019

Safe Clockwork

In this letter we demonstrate that safe quantum field theories can accommodate the clockwork mechanism upgrading it to a fundamental theory a lá Wilson. Additionally the clockwork mechanism naturally sources Yukawa hierarchies for safe completions of the Standard Model (SM). As proof of concept we investigate a safe Pati-Salam (PS) clockwork structure.

hep-ph↗

arXiv2018

$a$-theorem at large $N_f$

We determine the Jack and Osborn a-function and related metric for gauge-fermion theories to leading order in the large number of fermions and to all orders in the gauge coupling, demonstrating that the strong a-theorem is violated for the minimal choice of the a-function.

hep-th↗

arXiv2018

A complete asymptotically safe embedding of the Standard Model

We present and discuss the "Tetrad Model", a large colour/flavour embedding of the Standard model which has an interacting ultraviolet fixed point. It is shown that its extended-Pati-Salam symmetry is broken radiatively via the Coleman-Weinberg mechanism, while the remaining electroweak symmetry is broken when mass-squared terms run negative. In the IR the theory yields just the Standard Model, augmented by the fact that the Higgs fields carry the same generation indices as the matter fields. It is also shown that the Higgs mass-squareds develop a hierarchical structure in the IR, from a UV theory that is asymptotically flavour symmetric, opening up an interesting direction for explaining the emergence of the observed flavour structure.

hep-ph↗

arXiv2018

Safe Pati-Salam

We provide an asymptotically safe Pati-Salam embedding of the Standard Model. Safety is achieved by adding to the theory gauged vector-like fermions and by employing recently developed large number-of-flavor techniques and results. We show that the gauge, scalar quartic and Yukawa couplings achieve an interacting ultraviolet fixed point below the Planck scale. The minimal model is a relevant example of a Standard Model extension in which unification of all type of couplings occurs because of a dynamical principle, i.e. the presence of an ultraviolet fixed point. This extension differs from the usual Grand Unified Theories scenario in which only gauge couplings unify and become free with the remaining couplings left unsafe. We find renormalization group flow solutions that match the Standard Model couplings values at low energies allowing for realistic safe extensions of the Standard Model.

hep-ph↗

arXiv2018

Conformal Data of Fundamental Gauge-Yukawa Theories

We determine central charges, critical exponents and appropriate gradient flow relations for nonsupersymmetric vector-like and chiral Gauge-Yukawa theories that are fundamental according to Wilson and that feature calculable UV or IR interacting fixed points. We further uncover relations and identities among the various local and global conformal data. This information is used to provide the first extensive characterisation of general classes of free and safe quantum field theories of either chiral or vector-like nature via their conformal data. Using large $N_f$ techniques we also provide examples in which the safe fixed point is nonperturbative but for which conformal perturbation theory can be used to determine the global variation of the $a$ central charge.

hep-th↗

arXiv2018

Gauge-Yukawa theories: Beta functions at large $N_f$

We consider the dynamics of gauge-Yukawa theories in the presence of a large number of matter constituents. We first review the current status for the renormalization group equations of gauge-fermion theories featuring also semi-simple groups. In this regime these theories develop an interacting ultraviolet fixed point that for the semi-simple case leads to a rich phase diagram. The latter contains a complete asymptotically safe fixed point repulsive in all couplings. We then add two gauged Weyl fermions belonging to arbitrary representations of the gauge group and a complex, gauged scalar to the original gauge-fermion theory allowing for new Yukawa interactions and quartic scalar self-coupling. Consequently, we determine the leading $1/N_f$ Yukawa and quartic beta functions. Our work elucidates, consolidates and extends results obtained earlier in the literature. We also acquire relevant knowledge about the dynamics of gauge-Yukawa theories beyond perturbation theory. Our findings are applicable to any extension of the standard model featuring a large number of fermions such as asymptotic safety.

hep-ph↗

arXiv2018

Asymptotically Safe Standard Model Extensions?

We consider theories with a large number $N_F$ of charged fermions and compute the renormalisation group equations for the gauge, Yukawa and quartic couplings resummed at leading order in $1/N_F$. We construct extensions of the Standard Model where SU(2) and/or SU(3) are asymptotically safe. When the same procedure is applied to the Abelian U(1) factor, we find that the Higgs quartic can not be made asymptotically safe and stay perturbative at the same time.

hep-ph↗

arXiv2018

Safe and free instantons

We investigate the instanton dynamics of asymptotically safe and free quantum field theories featuring respectively controllable ultraviolet and infrared fixed points. We start by briefly reviewing the salient points about the instanton calculus for pure Yang Mills (YM) and QCD. We then move on to determine the role of instantons within the controllable regime of the QCD conformal window. In this region we add a fermion-mass operator and determine the density of instantons per unit volume as function of the fermion mass. Finally, for the first time, we extend the instanton calculus to asymptotically safe theories.

hep-th↗

arXiv2018

Asymptotically Safe Standard Model via Vector-Like Fermions

We construct asymptotically safe extensions of the Standard Model by adding gauged vector-like fermions. Using large number-of-flavour techniques we argue that all gauge couplings, including the hypercharge and, under certain conditions, the Higgs coupling can achieve an interacting ultraviolet fixed point.

hep-ph↗

arXiv2018

The high energy fate of the minimal Goldstone Higgs

We consider a minimal model where the Higgs boson arises as an elementary pseudo-Nambu-Goldstone boson. The model is based on an extended scalar sector with global SO(5)/SO(4) symmetry. To achieve the correct electroweak symmetry breaking pattern, the model is augmented either with an explicit symmetry breaking term or an extra singlet scalar field. We consider separately both of these possibili- ties. We fit the model with the known particle spectrum at the electroweak scale and extrapolate to high energies using renormalization group. We find that the model can remain stable and perturbative up to the Planck scale provided that the heavy beyond Standard Model scalar states have masses in a narrow interval around 3 TeV.

hep-ph↗

arXiv2017

Flavor Physics and Flavor Anomalies in Minimal Fundamental Partial Compositeness

Partial compositeness is a key ingredient of models where the electroweak symmetry is broken by a composite Higgs state. Recently, a UV completion of partial compositeness was proposed, featuring a new strongly coupled gauge interaction as well as new fundamental fermions and scalars. We work out the full flavor structure of the minimal realization of this idea and investigate in detail the consequences for flavor physics. While CP violation in kaon mixing represents a significant constraint on the model, we find many viable parameter points passing all precision tests. We also demonstrate that the recently observed hints for a violation of lepton flavor universality in $B\to K^{(*)}\ell\ell$ decays can be accommodated by the model, while the anomalies in $B\to D^{(*)}τν$ cannot be explained while satisfying LEP constraints on $Z$ couplings.

hep-ph↗

arXiv2017

Minimal Fundamental Partial Compositeness

Building upon the fundamental partial compositeness framework we provide consistent and complete composite extensions of the standard model. These are used to determine the effective operators emerging at the electroweak scale in terms of the standard model fields upon consistently integrating out the heavy composite dynamics. We exhibit the first effective field theories matching these complete composite theories of flavour and analyse their physical consequences for the third generation quarks. Relations with other approaches, ranging from effective analyses for partial compositeness to extra dimensions as well as purely fermionic extensions, are briefly discussed. Our methodology is applicable to any composite theory of dynamical electroweak symmetry breaking featuring a complete theory of flavour.

hep-ph↗

arXiv2017

Uncovering new strong dynamics via topological interactions at the 100 TeV collider

In models of composite Higgs dynamics new composite pseudoscalars can interact with the Higgs and electroweak gauge bosons via anomalous interactions, stemming from the topological sector of the underlying theory. We show that a future 100 TeV proton-proton collider (FCC-pp) will be able to test this important sector and thus shed light on the strong dynamics which generates the Higgs and other composite states. To elucidate our results we focus on the topological interactions of a minimal composite Higgs model with a fermionic ultraviolet completion, based on the coset $\text{SU}(4)/\text{Sp}(4)$. We suggest the strategy to test these interactions at the FCC-pp and analyse the expected reach.

hep-ph↗

arXiv2017

Safe SUSY

We investigate the short distance fate of distinct classes of not asymptotically free supersymmetric gauge theories. Examples include super QCD with two adjoint fields and generalised superpotentials, gauge theories without superpotentials and with two types of matter representation and semi-simple gauge theories such as quivers. We show that for the aforementioned theories asymptotic safety is nonperturbatively compatible with all known constraints.

hep-th↗

arXiv2017

Revealing BSM composite dynamics via topological interactions at future colliders

In composite Higgs models, new composite pseudoscalars can interact with the Higgs and with electroweak gauge bosons via anomalous interactions, which stem from the topological structure of the underlying theory. A future 100 TeV pp collider (FCC-pp) will be able to test these anomalous interactions and thus shed light on the strong dynamics which generates the Higgs and other composite resonances. We will discuss the topological interactions of a minimal composite Higgs model with fermionic ultraviolet completion, based on the coset SU(4)/Sp(4). We will indicate the strategy to test these interactions at the FCC-pp and the expected reach.

hep-ph↗

arXiv2017

Naturalness of asymptotically safe Higgs

We extend the list of theories featuring a rigorous interacting ultraviolet fixed point by constructing the first theory featuring a Higgs-like scalar with gauge, Yukawa and quartic interactions. We show that the theory enters a perturbative asymptotically safe regime at energies above a physical scale $Λ$. We determine the salient properties of the theory and use it as a concrete example to test whether scalars masses unavoidably receive quantum correction of order $Λ$. Having at our dispose a calculable model allowing us to precisely relate the IR and UV of the theory we demonstrate that the scalars can be lighter than $Λ$. Although we do not have an answer to whether the Standard Model hypercharge coupling growth towards a Landau pole at around $Λ\sim 10^{40}$ GeV can be tamed by non-perturbative asymptotic safety, our results indicate that such a possibility is worth exploring. In fact, if successful, it might also offer an explanation for the unbearable lightness of the Higgs.

hep-ph↗