# Florence Particle Physics and Cosmology Group

## Model Building

Traditionally a strong motivation for physics beyond the Standard Model has been the hierarchy problem, the inexplicable smallness of the electro-weak scale compared to the Planck scale. Our group entertained long term interest in the possibility that new strong dynamics explains this puzzle. The modern realization of this idea is composite Higgs models where the Higgs boson is a composite state of new strong dynamics, in particular as Nambu-Goldstone boson of a new sector. This allows to reproduce experimental results with definite predictions for deviations from the SM prediction. These models are currently tested at LHC and will be the focus of future colliders.

More recently a different approach has been been pursued by our group which ignores in first approximation the hierarchy problem. This possibility is hinted by the lack of any new physics signal in collider experiments and by the elegance of the SM in explaining experimental data. Very simple extensions of the SM can be build assuming that the new sector does not break the electro-weak symmetry which do not require ad hoc assumptions to comply with experimental data. In particular a new gauge theory with fermions vectorial under the SM is as successful as the SM for what concerns flavor physics and precision tests but new particles could be directly produced at colliders. These new sectors could give rise to a variety of experimental signatures. Most notably they provide dark matter candidates in the form of hadrons of the dark gauge group.

• [1] G.Panico and A.Wulzer, The Composite Nambu-Goldstone Higgs, Lect. Notes Phys. 913, pp.1 (2016), [arXiv:1506.01961 [hep-ph]]
• [2] D.Barducci, S.De Curtis, M.Redi and A.Tesi, An almost elementary Higgs: Theory and Practice, JHEP 1808, 017 (2018) [arXiv:1805.12578 [hep-ph]]

## Collider Physics

Collider physics has been for over 50 years the pillar of particle physics. Studying the collisions of elementary particles at high energies has allowed to understand the laws that control the universe up to distances as short as 10-17 cm. This knowledge has led to the Standard Model of elementary particles a theory that, rather surprisingly, so far describes with exquisite precision all the measurements. This program has culminated in 2012 when the Higgs boson, the last missing piece of the SM, has been discovered at the Large Hadron Collider at CERN. Having established the SM the next step will be the hunt for physics beyond the SM required to explain the many mysteries of our universe. Our group is interested both in LHC physics and future collider programs for the search of physics beyond the SM.

## Dark Matter

We know that DM exists and dominates the matter density of the universe but we don't know what it is made of. Our group has a broad interests in both theoretical and experimental aspects of this field. In a series of papers we developed scenarios where DM is a bound state of new strong dynamics. In the simplest realization DM is a baryon of a dark gauge group allowing to explain the cosmological stability of DM in a natural way. DM is one particle of a dark sector in analogy with the SM. These scenarios give novel signatures such as DM nuclei formation of experimental interest. A different possibility is a classical field that oscillates. The most minimal possibility is the QCD axion which also solves the strong CP problem in the SM.

• [1] O. Antipin, M. Redi, A. Strumia and E. Vigiani, Accidental Composite Dark Matter,'' JHEP {\bf 1507}, 039 (2015)

## Gravitational Waves

With the detection of the first gravity wave signal in 2016 by the LIGO-VIRGO collaboration a new era has began in the study of the universe. Our knowledge of the universe has relied almost entirely on the electromagnetic radiation that travels from remote corners of the cosmos up to us today. Gravity waves are a new probe that allows us to look at the universe from a completely new standpoint.

This exciting subject is still in its infancy and likely we are just scratching the surface of what we can learn from these observations. So far gravity waves have been measured in extreme astrophysical events such us merging of black-holes. In the future it will be possible to probe other kinds of gravitational waves produced when the universe was less than 1 second old. This opens up the possibility to look directly at the universe even where the electro-magnetism is blind and only indirect informations can be obtained.

Our group has recently entered this field with particular interest in gravity waves from phase transitions predicted in many extensions of the Standard Model such as baryogenesis or theories of Dark Matter. Observing these types of gravity waves would be a clear signal of physics beyond the SM.

Last updated: November 2019