arXiv subjects

Antti Vaihkonen

Publications and source records attributed to Antti Vaihkonen.

5 recordsLinked to original sources

arXiv2005

Comment on non-Gaussianity in hybrid inflation

In the literature there have been incompatible estimates for the amount of non-Gaussianity in hybrid inflation. In this note we point out the sources for the discrepancies and show that the results for the amount of non-Gaussianity in hybrid inflation obtained by two different methods, namely, perturbing Einstein equation to second order and the separate universe approach, indeed are compatible. This provides confidence in the methods themselves and in the actual computation of non-Gaussianities.

astro-ph↗

arXiv2005

Cosmological constraints on string scale and coupling arising from tachyonic instability

We demonstrate that string motivated inflation ending via tachyonic instability leaves a detectable imprint on the cosmic microwave background (CMB) radiation by virtue of the excitation of non-Gaussian gravitational fluctuations. The present WMAP bound on non-Gaussianity is shown to constrain the string scale by $M_S/M_P\leq 10^{-4}$ for string coupling $g_{s}<0.1$, hence improving the existing bounds. If tachyon fluctuations during inflation are not negligible, we find the stringent constraint $g_s\sim 10^{-9}$ for $M_{S}/M_{P}<10^{-3}$. This case may soon be ruled out by the forthcoming CMB non-Gaussinianity bounds.

hep-th↗

arXiv2005

Non-Gaussianity from Instant and Tachyonic Preheating

We study non-Gaussianity in two distinct models of preheating: instant and tachyonic. In instant preheating non-Gaussianity is sourced by the local terms generated through the coupled perturbations of the two scalar fields. We find that the non-Gaussianity parameter is given by $f_{NL}^ϕ\sim 2g < O(1)$, where $g$ is a coupling constant, so that instant preheating is unlikely to be constrained by WMAP or Planck. In the case of tachyonic preheating non-Gaussianity arises solely from the instability of the tachyon matter and is found to be large. We find that for single field inflation the present WMAP data implies a bound $V_{0}^{1/4}/M_{P}\leq 10^{-4}$ on the scale of tachyonic instability. We argue that the tachyonic preheating limits are useful also for string-motivated inflationary models.

hep-ph↗

arXiv2005

Non-Gaussianity from Preheating

We consider a two-field model for inflation where the second order metric perturbations can be amplified by a parametric resonance during preheating. We demonstrate that there can arise a considerable enhancement of non-Gaussianity sourced by the local terms generated through the coupled perturbations. We argue that the non-Gaussianity parameter could be as large as f_{NL} ~ 50. Our results may provide a useful test of preheating in future CMB experiments.

astro-ph↗

arXiv2004

Non-Gaussian perturbations in hybrid inflation

We consider second order inflationary perturbations in the case of two scalar fields, $σ$ and the inflaton $ϕ$. We derive an expression for the non-Gaussianity of perturbations and apply the results to hybrid inflation. We isolate the contributions due to $σ$ and evaluate the resulting terms to show that $σ$-induced non-Gaussianities dominate over inflaton-induced non-Gaussianities when $m^2_σ \gtrsim ηH^2$, where $η$ is the slow-roll parameter. This may provide a useful test of hybrid inflation in forthcoming CMB experiments.

hep-ph↗