arXiv subjects

Jason Kristiano

Publications and source records attributed to Jason Kristiano.

10 recordsLinked to original sources

arXiv2026

Effective Dynamics of Inflationary End-of-the-World Branes in AdS$_3$

We develop an effective description of a two-dimensional cosmological end-of-the-world brane embedded in AdS$_3$, with a scalar field localized on the brane. Integrating out bulk degrees of freedom, especially in the small-gradient regime, the effective action reduces to a Liouville-like theory coupled to the brane scalar. We then construct brane trajectories whose induced geometry realizes slow-roll inflation and reconstruct the associated scalar profile and potential. We also study regular Euclidean brane geometries that admit a smooth continuation to Lorentzian de Sitter and inflationary universes, and evaluate the semiclassical on-shell action for the de Sitter solution. Finally, we analyze linearized inhomogeneous perturbations and find no exponentially growing mode within the regime of validity of the approximation.

hep-th↗

arXiv2025

Imprints of flat space analyticity in de Sitter S-matrix

The analytic structure of the flat-space S-matrix provides non-perturbative constraints on low-energy effective field theories based on the properties of high-energy theory. While the analytic structure of the flat-space S-matrix is well understood, extending this framework to de Sitter space is challenging, as the expanding background complicates the definition of asymptotic states and breaks time-translation symmetry. This paper investigates how flat-space analyticity is imprinted on the de Sitter S-matrix. We derive a relation between flat-space amplitude and de Sitter S-matrix on a specific limit called the Hubble flat-space limit. Specifically, we show that the relation holds for tree-level amplitude exchanging a massive scalar field with any local derivative interactions. Finally, we argue that the Hubble flat-space limit is more compatible with the description of effective field theory, as the total energy dependence of de Sitter S-matrix becomes trivial, allowing the Mandelstam variable to be identified as the unique energy scale, just as in flat space.

hep-th↗

arXiv2025

Inflationary background renormalization

In cosmic inflation, non-linearities of the curvature perturbation can induce backreaction to the background. To obtain observational predictions at non-linear order on the correct background, one has to redefine the background or introduce background renormalization. We explicitly demonstrate it with a vanishing one-point function of the curvature perturbation as a renormalization condition, so that proper observational predictions can be made even at the nonlinear level. Due to non-linear symmetry of the curvature perturbation, such a procedure induces corrections to the two-point functions, which yield a finite renormalized one-loop correction that depends on the regularization scheme. Cancellation of the divergence is a manifestation of Maldacena's consistency condition. The finite term can be large and highly time-dependent, which indicates evolution outside the horizon.

hep-th↗

arXiv2024

Generating large primordial fluctuations in single-field inflation for PBH formation

In order to produce appreciable amount of primordial black holes (PBHs), the square amplitude of curvature perturbation must take a large value of $\mathcal{O}(0.01)$, namely, seven digits larger than the value observed by cosmic microwave background radiation (CMB) on large scales. Such a large fluctuation can be achieved by violating the slow-roll (SR) condition within a short duration. The best known of such possibilities is the ultraslow-roll (USR) inflation. We calculate the power spectrum of curvature perturbation in a simple single-field inflation model which evolves through the SR-USR-SR regimes so that both large-amplitude small-scale fluctuation for PBH formation and small-amplitude large-scale fluctuation as observed by CMB are realized. We further calculate the bispectrum and one-loop correction to the power spectrum induced by the third-order action of curvature perturbation as the beginning of precision cosmology on small scales. As a result, we show that single-field inflation model realizing PBH formation can be constrained by the quantum correction.

astro-ph.CO↗

arXiv2024

Comparing sharp and smooth transitions of the second slow-roll parameter in single-field inflation

In single-field inflation, violation of the slow-roll approximation can lead to growth of curvature perturbation outside the horizon. This violation is characterized by a period with a large negative value of the second slow-roll parameter. At an early time, inflation must satisfy the slow-roll approximation, so the large-scale curvature perturbation can explain the cosmic microwave background fluctuations. At intermediate time, it is viable to have a theory that violates the slow-roll approximation, which implies amplification of the curvature perturbation on small scales. Specifically, we consider ultraslow-roll inflation as the intermediate period. At late time, inflation should go back to the slow roll period so that it can end. This means that there are two transitions of the second slow-roll parameter. In this paper, we compare two different possibilities for the second transition: sharp and smooth transitions. Focusing on effects generated by the relevant cubic self-interaction of the curvature perturbation, we find that the bispectrum and one-loop correction to the power spectrum due to the change of the second slow-roll parameter vanish if and only if the Mukhanov-Sasaki equation for perturbation satisfies a specific condition called Wands duality. We also find in the case of sharp transition that, even though this duality is satisfied in the ultraslow-roll and slow-roll phases, it is severely violated at the transition so that the resultant one-loop correction is extremely large inversely proportional to the duration of the transition.

astro-ph.CO↗

arXiv2023

Note on the bispectrum and one-loop corrections in single-field inflation with primordial black hole formation

Primordial black holes can be formed from the collapse of large-amplitude perturbation on small scales in the early Universe. Such an enhanced spectrum can be realized by introducing a flat region in the potential of single-field inflation, which makes the inflaton go into a temporary ultraslow-roll period. In this paper, we calculate the bispectrum of curvature perturbation in such a scenario. We explicitly confirm that bispectrum satisfies Maldacena's theorem. At the end of the ultraslow-roll period, the bispectrum is generated by bulk interaction and field redefinition. At the end of inflation, bispectrum is generated only by bulk interaction. We also calculate the one-loop correction to the power spectrum from the bispectrum, called the source method. We find it consistent with the calculation of the one-loop correction from the second-order expansion of in-in perturbation theory.

hep-th↗

arXiv2022

Constraining Primordial Black Hole Formation from Single-Field Inflation

The most widely studied formation mechanism of a primordial black hole is collapse of large-amplitude perturbation on small scales generated in single-field inflation. In this Letter, we calculate one-loop correction to the large-scale power spectrum in a model with sharp transition of the second slow-roll parameter. We find that models producing an appreciable amount of primordial black holes induce nonperturbative coupling on a large scale probed by cosmic microwave background radiation. Our result implies that a small-scale power spectrum can be constrained by large-scale cosmological observations.

hep-th↗

arXiv2022

Perturbative region on non-Gaussian parameter space in single-field inflation

We calculate one-loop correction to the two-point functions of curvature perturbation in single-field inflation generated by cubic self-interaction. Incorporating the observed red-tilted spectrum of curvature perturbation, the relevant one-loop correction takes a finite value and inversely proportional to the spectral tilt. Requiring one-loop correction to be much smaller than the tree-level contribution leads to an upper bound on primordial non-Gaussianity. While observationally allowed region of non-Gaussian parameter space is found to be entirely included by the region, where one-loop correction is smaller than the tree-level contribution, an appreciably large region has one-loop correction larger than 1% or even 10% of the latter. If future observations conclude non-Gaussianity falls in such a region, then it would be important to incorporate higher-order corrections to the spectrum in order to achieve precise cosmology. In some extreme cases, where one-loop correction has a comparable magnitude to the tree-level contribution, it might indicate breakdown of the cosmological perturbation theory in the context of single-field inflation.

hep-th↗

arXiv2022

Why Must Primordial Non-Gaussianity Be Very Small?

One-loop correction to the power spectrum in generic single-field inflation is calculated by using standard perturbation theory. Because of the enhancement inversely proportional to the observed red tilt of the spectral index of curvature perturbation, the correction turns out to be much larger than previously anticipated. As a result, the primordial non-Gaussianity must be much smaller than the current observational bound in order to warrant the validity of cosmological perturbation theory.

hep-th↗

arXiv2019

Magnetic Tip Trap System

We report a detailed theoretical model of recently-demonstrated magnetic trap system based on a pair of magnetic tips. The model takes into account key parameters such as tip diameter, facet angle and gap separation. It yields quantitative descriptions consistent with experiments such as the vertical and radial frequency, equilibrium position and the optimum facet angle that produces the strongest confinement. We arrive at striking conclusions that a maximum confinement enhancement can be achieved at an optimum facet angle $θ_{max}=\arccos{\sqrt{2/3}}$ and a critical gap exists beyond which this enhancement effect no longer applies. This magnetic trap and its theoretical model serves as a new and interesting example of a simple and elementary magnetic trap in physics.

physics.class-ph↗