BEGIN:VCALENDAR VERSION:2.0 PRODID:-//linuxsoftware.nz//NONSGML Joyous v1.4//EN BEGIN:VEVENT SUMMARY:Cosmological gravitational particle production: Scalars and fermio ns DTSTART:20251216T160000Z DTEND:20251216T180000Z DTSTAMP:20260923T225501Z UID:6349fdb8-7184-4201-96d4-718612518981 SEQUENCE:2 CREATED:20251125T095650Z DESCRIPTION:Particle production in the Early Universe is one of the corner stones of modern cosmology and plays an important role in dark-matter phen omenology. In this talk\, I will discuss the gravitational production of s calars and fermions during inflation. For scalars\, I will compare Bogolyu bov coefficient and Starobinsky stochastic approaches\, showing that they only agree in the limit of infinitely long inflation. High-scale inflation is very efficient in particle production\, leading to constraints on the existence of free\, light\, and stable scalars: such particles are viable only if their masses are below the eV scale or if the reheating temperatur e is in the GeV range. For fermions\, I will show how the production effic iency depends on the particle mass\, which is generated via the Yukawa cou pling and sensitive to the corresponding scalar field value. Scalar fields can experience large quantum fluctuations during inflation\, driving the average field to the Hubble scale and above. Thus\, fermions can be very h eavy during inflation\, enhancing particle production. This mechanism can be the leading source of right-handed neutrinos\, if they gain a Majorana mass from the Yukawa coupling to a singlet scalar. LAST-MODIFIED:20251125T095738Z LOCATION:DF Seminar Room (2-8.3)\, 2nd floor of Physics Building URL:http://df.vps.tecnico.ulisboa.pt/pt/eventos/cosmological-gravitational -particle-production-scalars-and-fermions/ X-ALT-DESC;FMTTYPE=text/html:

Particle production in the Early Universe is one of the cornerstones of modern cosmology and plays an important role in dark-matter phenomenology. In this talk\, I wil l discuss the gravitational production of scalars and fermions during infl ation. For scalars\, I will compare Bogolyubov coefficient and Starobinsky stochastic approaches\, showing that they only agree in the limit of infi nitely long inflation.

High-scale inflation is very efficient in particle production\, leading to constraints on the existence of free\, l ight\, and stable scalars: such particles are viable only if their masses are below the eV scale or if the reheating temperature is in the GeV range . For fermions\, I will show how the production efficiency depends on the particle mass\, which is generated via the Yukawa coupling and sensitive t o the corresponding scalar field value.

Scalar fields can experi ence large quantum fluctuations during inflation\, driving the average fie ld to the Hubble scale and above. Thus\, fermions can be very heavy during inflation\, enhancing particle production. This mechanism can be the lead ing source of right-handed neutrinos\, if they gain a Majorana mass from t he Yukawa coupling to a singlet scalar.

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