REMINDER - High Energy Physics Seminar TODAY - Kalia

[HECAP - Margherita Di Giovannantonio]

*_HIGH ENERGY PHYSICS SEMINARS_*
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*Thursday, 23 July *2026, at *16:00* - *_Euler Lecture 
Hall_***-*https://indico.ictp.it/event/11390/*


Saarik Kalia (IFAE, Barcelona)


*“Dynamically Generated Tilt of Isocurvature Fluctuations**"*
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_Abstract_

Light scalar fields acquire isocurvature fluctuations during inflation. 
While these fluctuations could lead to interesting observable signatures 
at small scales, they are strongly constrained on large scales by cosmic 
microwave background observations. When the mass of the scalar is much 
lighter than the inflationary Hubble scale, $m\ll H_I$, the spectrum of 
these fluctuations is flat. Meanwhile, if $m\gg H_I$, the fluctuations 
are suppressed. A blue-tilted isocurvature spectrum which exhibits 
enhanced structure on small scales but avoids observational constraints 
on large scales therefore requires a coincidence of scales $m\sim H_I$ 
for a free massive scalar. In this talk, I will show that if a scalar 
field possesses a nontrivial potential, its inflationary dynamics 
naturally cause this condition to be satisfied, and so a blue-tilted 
spectrum is generically expected for a large class of potentials. 
Specifically, if its potential $V$ exhibits a region which satisfies the 
slow-roll condition $V''<3H_I^2$, the scalar condensate will spend most 
of inflation close to the boundary of this region, so that its effective 
mass is typically close to $H_I$. The resulting blue tilt is inversely 
proportional to the number of $e$-folds of inflation prior to horizon 
crossing. If the scalar is long-lived, this mechanism leads to an 
attractor prediction for its relic abundance, which is insensitive to 
initial conditions of the scalar. In particular, a scalar field with 
quartic self-interactions can achieve the correct abundance to 
constitute all of the dark matter for a wide range of masses. I will 
show the relationship between the mass and self-coupling of quartic dark 
matter predicted by this mechanism.