Scientific activities of the various Research Units

---

The High Energy Frontier

Beyond the Higgs boson, the LHC has found no evidence of new physics at the TeV
scale. One of the primary objectives of the LHC, its High Luminosity upgrade (HLLHC),
and future colliders is now to investigate whether a Higgs doublet is the sole
responsible for electroweak symmetry breaking. To achieve this important goal it is
necessary to perform a precise investigation of the Higgs boson properties and
accurate measurements of the interactions among the SM particles, which itself
requires both extremely accurate predictions for Standard Model processes as well as
a theoretical framework for new physics.
— The Effective field theories present a natural theoretical framework for
parameterizing new physics effects in the absence of evidence of new resonances. We
plan to employ the SM effective field theory (SMEFT) to investigate the signatures of a
large class of heavy new physics models. We will study how the new couplings can be
constrained at the LHC and future colliders, as well as how the associated operators
might be generated by realistic UV scenarios. A special focus will be on the Higgs selfcouplings
and interactions modifying the small Yukawa couplings. (PD,TS)
— It is crucial to identify the most sensitive experimental strategies for measuring and
constraining the new interactions appearing in the SMEFT. We plan to study differential
observables that can qualitatively and quantitatively improve the sensitivity of LHC to
new physics searches. In particularly we will focus on the diboson production, quark
anti-quark collisions, and vector boson fusion processes. Special attention will be paid
to the possibility of applying machine learning techniques to boost further the power of
the experimental search. (TS)
— We will provide precise predictions for Higgs processes. Gluon fusion processes
mediated by top quark loops are part of many processes relevant to Higgs physics.
Higher order corrections turn out to be numerically very relevant and hence need to be
taken into account. In some cases, standard methods like a large top mass expansion
have very limited validity and new techniques must be developed. (PD)
The combination of techniques for the evaluation of Scattering Amplitudes within
Perturbation Theory together with the Effective Field Theory approach provides a
systematic and universal technology for quantifying effects beyond the leading order in
the study of high energy processes.
— We plan to develop a novel mathematical framework for field theoretic calculations
which makes systematic use of intersection theory, for the automatic evaluation of
multiloop Feynman amplitudes. As recently discovered, using intersection theory, the
evaluation of scattering amplitudes can proceed in a purely algebraic way, like the
decomposition of a vector in a vector space. The research in this direction is highly
interdisciplinary, involving many formal areas of theoretical high-energy physics. (PD)
— Future hadron and linear colliders will operate at energies never probed before. We
plan to develop new techniques and formalisms that allow us to directly access the
leading high energy behavior of electroweak processes. (PD)
— The lack of evidence of new physics at the TeV scale suggests our perspective on
the hierarchy problem, and in fact on the entire field of Physics Beyond the SM, might
need a change of paradigm. We will thus explore novel approaches to model-building
in light of this puzzling state of affairs. (PD, TS)

 

The Intensity Frontier

— The long-standing muon g-2 discrepancy is one of the most intriguing hints of New
Physics emerged so far in particle physics. In the near future the experimental
precision in its measurement will be significantly improved, and for this reason
considerable effort is being devoted to reduce the theoretical uncertainty in the SM
prediction, currently dominated by the hadronic corrections. A novel approach has been
proposed to infer the latter via the measurement of elastic scattering of high-energy
muons on atomic electrons, an idea at the heart of the proposal of the MUonE
experiment (under testing phase at CERN). For this new approach to be competitive
with more conventional ones, theoretical predictions for electron-muon scattering
should be calculated at the highest available precision. We plan to study electron-muon
scattering at NNLO. (PD)
— We plan to classify new physics explanations of the muon g-2 anomaly and
investigate their main direct and indirect signatures in the light of all currently available
experimental data. Moreover, since also the electron g-2 has recently exhibited an
anomaly, we will investigate the flavour structure required for new physics scenarios in
order to simultaneously account for both anomalies while being compatible with the
tight constraints from flavour data. (PD)
— The evaluation of scattering amplitudes involving massive particles, both as virtual
and external states can be relevant both for high-energy and high-intensity research. In
the latter case, our two-fold objective aims at providing higher-order QED corrections to
muon-electron scattering relevant for the analyses of the MUonE experiments, as well
as for the related di-muon production at $e^+ e^-$-machines, of interest for the BES
and Belle experiments. Top-pair production in hadronic collisions shares many
mathematical features with muon-pair production. Therefore, we expect to improve the
analytic understanding of this process as well. (PD)
— The flavor puzzle remains one of the most unexplained aspects of the Standard
Model. We will continue to explore models for the fermions mass spectrum. More
specifically, we plan to analyze modular invariant models of fermion masses. Modular
invariance can highly constrain the superpotential in this class of models, to the point of
pinning down all Yukawa couplings in terms of the modulus field, up to an overall
constant. On the contrary, the Kahler potential is much less constrained. We aim to
investigate possible constraints on the Kahler potential arising by 1) enhanced
symmetry points in moduli space, 2) consistency conditions such as positivity and 3)
asymptotic requirements. Exploiting these extra requirements, we also aim to build
realistic models for lepton masses and mixing angles. (PD,TS)
— If the present deviations from the SM in B-physics persist in the new experimental
data, this would represent the first real evidence for physics beyond the SM at an
energy scale close to the TeV. In this case our focus will be on developing consistent
new physics models able to reproduce the observed signals, and derive the predictions
for other low- and high-energy observables, which will be able to probe such models.
The connection to high-energy searches at the LHC, and the study of prospects for
future colliders, will also be an important part of this research line. In this respect we
plan to investigate new ways to improve experimental searches of these new physics
models. For example, requiring a b-tagged jet in the final state is expected to improve
the sensitivity on interactions involving the bottom quark. Such experimental analyses
are still lacking, and it is important to quantify the improvement expected using these
techniques. (TS)

— Since no convincing evidence of heavy new physics has emerged yet, scenarios
with new light mediators have received increasing attention from both experimental and
theoretical communities over the past several years. A prominent example are SM
extensions with light pseudo-scalar bosons, generically referred to as axion-likeparticles
(ALPs). We plan to thoroughly explore the low-energy signatures of ALPs in
quark and lepton flavor violating observables as well as in electric dipole moments of
atomic and nuclear systems generalising and complementing previous results available
in the literature. (PD)

 

The Astroparticle Frontier

About one-fourth of the energy budget of the Universe today consists of dark matter.
Despite overwhelming evidence of its presence, identifying its nature remains one of
the most fundamental open question in particle physics. Null results at the LHC and
underground direct detection experiments put severe stress on one of the most popular
dark matter candidates, the weakly interacting massive particle (WIMP). Our project will
investigate the viability of other compelling alternatives: dark sectors with feeble
couplings to the SM, the QCD axion and axion-like particles, and primordial black
holes. In particular, we plan to investigate the following aspects.
— Dark sectors could be extremely simple and minimal but may as well conceal a rich
and intricate structure with matter and forces of its own. We plan to investigate novel
direct and indirect detection signals, for instance due to the presence of possible longrange
forces and milli-charges carried by dark matter. (PD,TS)
— We aim to investigate several aspects of axion physics, mostly in the context of
cosmology and astrophysics. For example, axion’s quantum fluctuations during inflation
naturally induce isocurvature density fluctuations, which could leave a distinctive
imprint on the cosmic microwave background spectrum. By looking for these traces on
the CMB, one can constrain axion properties as well as the physics of inflation. Another
interesting research project focuses on the ultra-light mass range. Such axions have
large de Broglie wavelengths and affect structure formation of the Universe at small
scales. We plan to explore this aspect and assess the capabilities of existing and
upcoming experiments in disentangling the new physics effects. Ultra-light axions can
also trigger superradiance instability of rotating black holes. We plan to investigate
some of the details of the superradiance process which in the presence of scalar selfinteractions
is not yet fully understood. (TS)
— Dark matter could consist of black holes of primordial origin. A full understanding of
this scenario requires a comprehensive study of the evolution of the Universe from the
inflationary epoch to the present day. Primordial black holes could for example
originate from curvature perturbations generated during inflation and later transferred
to the radiation density field. We plan to investigate which class of inflationary models
are best-suited to generate large enough perturbations and assess possible
alternatives to this formation mechanism. The process of gravitational collapse that
leads to black hole formation is not fully understood and requires a careful statistical
analysis of density perturbations beyond the gaussian approximation. In this respect,
we plan to characterize and investigate the role of non-gaussianities. After their
formation in the radiation epoch, the primordial black holes cross the entire evolution of
the Universe. We plan to investigate possible imprints left by primordial black holes
during this evolution history, from late time to the present epoch. (TS)
The same types of integrals appearing in relativistic, quantum scattering processes,
also appear in the description of non-relativistic, classical systems. For this reason
Feynman calculus and scattering amplitudes techniques provide an efficient strategy to
go beyond the state of the art in the Astroparticle, Astrophysics, Cosmology
communities, becoming systematic tools to be considered together with more
traditional ones.
— In this respect we plan to perform the evaluation of post-Newtonian and post-
Minkowskian corrections to the interaction potential of black-hole/binary astrophysical
systems, which is necessary to prepare templates for the discrimination of
gravitational-wave signals. (PD)