TAsP

The Theoretical Astroparticle Physics (TAsP) research group at LNF undertakes a vast and diversified research program at the crossroad between particle physics, astrophysics and cosmology. Deeper levels of theoretical understanding are clearly demanded by a number of unexplained phenomena, including the origin of neutrino masses and mixings, the puzzles of dark matter and dark energy, the asymmetry between matter and antimatter observed in the Universe, the origin and spectra of high-energy cosmic rays.

In recent years, the LNF group has explored various areas of astroparticle physics, ranging from dark matter model building, dark sector phenomenology containing hypothetical candidates for the dark matter, axion physics, and has developed possible explanations of the cosmological matter-antimatter asymmetry via the mechanism of leptogenesis.

• Dark Sectors. In synergy with the LNF PADME experimental group, the local TAsP group has explored the advantages of using positron beams as a tool for producing hypothetical new, light and feebly coupled particles. In particular, the resonant production of one type of such particles known as “dark photon” via positron annihilation of atomic electrons has been shown to represent a fundamentally important process that must be always included when studying dark photon production, not only at PADME but also at electron- and proton-beam facilities. The blue region in the picture gives an example of the new region in the mass-coupling plane that becomes experimentally accessible by considering resonant dark photon production. Turning to the future, the group is now exploring the foreseeable sensitivity of the PADME experiment in searching with this technique for the dark photon with a mass of 17 MeV that has been invoked to explain an intriguing anomaly detected in nuclear transitions of 8Be and more recently also of 4He.
• Axion Physics. Axions are yet undiscovered particles whose existence has been conjectured to explain why strong interactions conserve the charge-parity symmetry. The LNF-TAsP group carries out original researches in non-conventional axion models, elaborating their theoretical groundings and analysing their experimental prospects. For instance, the possibility of “astrophobic’’ axions, that is axions which would evade all the most stringent constraints from astrophysics observations, is an idea developed in Frascati jointly with international collaborators of the group. The picture is an artistic view of the interaction between one axion and two photons which is the most important process through which astrophobic axions could be detected.
• Neutrino physics. The flavour neutrino puzzle is often addressed by considering neutrino mass matrices with a certain number of vanishing entries, since a reduction in the number of free parameters increases the predictive power. Symmetries that can enforce textures zero can also enforce a more general type of structures with no vanishing entries, but at the same time maintaining the same predictive power. Recently the group has determined and classified all the Abelian symmetries that can produce this result and that have been denoted “covert symmetries”. The bell-shaped blue region in the picture represents the region of values of two neutrino parameters (the mixing angle θ23 and the phase δ) preferred by experimental results, while the dark-grey region depicts the prediction of a covert-symmetry model. This is a rather precise prediction that will be tested experimentally in the forthcoming years.
• Leptogenesis. The general theory of leptogenesis as a mechanism to explain the cosmological matter-antimatter asymmetry, with attention to its most striking phenomenological consequences, and including all the most recent refinements, keeps being one of the main research topic of the group, that is by now an internationally recognised scientific leadership in this field. Recent theoretical developments include studies of the effects of a non-standard cosmological history (such as an accelerated expansion period) on the numerical estimates of the matter-antimatter asymmetry produced via leptogenesis.