Within the framework of the inflationary paradigm, it is well-known that correlation functions (or in general bi-linear observables) of quantum fields on a curved background suffer from divergences. In general, the presence of ultraviolet (UV) divergences due to fluctuations on arbitrary short scales is a common aspect of quantum field theory. In flat space and for free theories, infinities can be removed by normal ordering, namely, by subtracting the expectation value of the vacuum energy. This is legitimate, indeed this contribution is not observable. Differently, in curved space-time such divergences cannot be easily cured as in flat space, since the vacuum is not unambiguously defined. A common prescription to renormalize divergent quantities in curved spacetime is based on the subtraction of the expectation value of the energy associated with the adiabatic vacuum, which minimizes the creation of particles due to the presence of a time-dependent metric. This method is therefore called adiabatic subtraction or regularization. In this seminar I will introduce a new approach to the adiabatic subtraction, in which a comoving infrared cut-off is introduced in the adiabatic counterpart of the physical quantity under consideration, building on the fact that the adiabatic subtraction procedure is ill defined when the scales of interest are stretched beyond the Hubble horizon. I will show how this infrared cut-off should be used to obtain a completely well-defined renormalization scheme and how it is fundamental to avoid unphysical divergences that can be generated by a pathological behavior of the adiabatic subtraction extended to the infrared tail of the spectrum . The infrared cut-off appears as a new degree of freedom introduced in the theory and its actual value has to be consistently fixed by a physical prescription. As an example, I will show how such degree of freedom can be set to obtain the correct value of the conformal anomaly in the symptomatic case of an inflationary model with gauge fields coupled to a pseudo-scalar inflaton. The infrared cut-off appears as a new degree of freedom introduced in the theory and its actual value has to be consistently fixed by a physical prescription. As an example, I will show how such degree of freedom can be set to obtain the correct value of the conformal anomaly in the symptomatic case of an inflationary model with gauge fields coupled to a pseudo-scalar inflaton. The infrared cut-off appears as a new degree of freedom introduced in the theory and its actual value has to be consistently fixed by a physical prescription. As an example, I will show how such degree of freedom can be set to obtain the correct value of the conformal anomaly in the symptomatic case of an inflationary model with gauge fields coupled to a pseudo-scalar inflaton.

## Dates:

Tuesday, 10 May, 2022 - 13:30 to 15:00

## Localisation / Location:

APC

## Salle / Local:

seminar room 483A, contact roperpol@apc.in2p3.fr for Zoom meeting details

- Séminaire

## Nom/Prénom // Last name/First name:

Chiara Animali

## Affiliation:

APC and Università de Pisa

## Equipe(s) organisatrice(s) / Organizing team(s):

- Théorie

## Pays / Country:

France