We propose a two-field model of warm inflation motivated by a heterotic string construction, involving an axion and a dilaton-like scalar field with non-trivial kinetic mixing. Gauge-field interactions generate dissipation and thermal corrections affecting both fields. A systematic numerical analysis reveals a range of dynamical regimes, including effectively single-field and multi-field behavior. We find that warm inflation is typically realized along the axion direction, while thermal corrections tend to hinder sustained dilaton-driven inflation over most of the parameter space. Although configurations exist in which the dilaton becomes dynamically relevant, particularly near the end of inflation, the majority of viable solutions are effectively single-field and axion-dominated. These results point to a dynamical mechanism in heterotic-inspired models that naturally favors axion-driven warm inflation while limiting the role of the dilaton.

United Kingdom

Arjun Berera

Canada

Heliudson Bernardo

India

Suddhasattwa Brahma

Jaime Calderón-Figueroa

Brazil

Rudnei Ramos

United States

Michael Toomey

Heterotic warm inflation

Stimulated emission is shown to be robust in stars. Through Bose enhancement this produces quantum states of aligned, monochromatic photons somewhat similar to a laser. The probability of creating such states is computed. We show that from the solar corona such quantum states would propagate outside of the solar region and through the Solar System without decoherence. For a <math><mrow><mn>1</mn><mtext>−</mtext><msup><mrow><mi>m</mi></mrow><mrow><mn>2</mn></mrow></msup></mrow></math> test detector at the distance of the Earth from the Sun, we estimate rates of such quantum states in the few per second thus potentially detectable. The same process should lead to such quantum states also arriving from stars at interstellar distances.

Ecuador

China

Liang Chen

Thomas W. Kephart

Astrophysically sourced quantum coherent photonic signals

Perturbative quantum corrections to primordial power spectra are important for testing the robustness and the regime of validity of inflation as an effective field theory. Although this has been done extensively for the density power spectrum (and, to some extent, for the tensor spectrum) using loop corrections, we do so in an open quantum system approach to the problem. Specifically, we calculate the first-order corrections to the primordial gravitational wave spectrum due to (cubic) tensor interactions alone. We show that our results match expectations from standard loop corrections only in the strict Markovian limit, and therefore, establish a systematic way to relax this approximation in the future, as is generally necessary for gravitational systems.

Quantum corrections to the primordial tensor spectrum: open EFTs &amp; Markovian decoupling of UV modes

We identify potential sources of decoherence for <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> gauge bosons from a cosmological standpoint. Besides interactions with different species in the cosmological medium, we also consider effects due to the expansion of the Universe, which can produce particles (especially scalars) that can potentially interact with the photon in a quantum state. We look in particular at the case of axionlike particles and their predicted decay channels in our analysis. These interactions are shown to have a negligible effect as far as decoherence goes. Interaction rates with cosmic microwave background radiation or through Thomson scattering are small, so that the interstellar medium remains the biggest decoherence factor. Thus, quantum teleportation experiments with photon energies in the range 1–10 keV should be feasible at cosmological distances up to the galaxy formation epoch or beyond (<math><mi>z</mi><mo>∼</mo><mn>100</mn></math>).

Robert Brandenberger

Alan Heavens

Quantum coherence of photons to cosmological distances

We consider thermal, trapped and chromo-natural inflation in light of the swampland criteria and the Trans-Planckian Censorship Conjecture (TCC). Since thermal inflation occurs at energies low compared to those of Grand Unification, it is consistent with the TCC, and it is also consistent with the refined swampland conditions. Trapped and chromo-natural inflation are candidates for primordial (high energy scale) inflation. Since in both of these scenarios there are effective damping terms in the scalar field equation of motion, the models can easily be consistent with the swampland criteria. The TCC, on the other hand, constrains these scenarios to only take place at low energies.

Iran

Vahid Kamali

Thermal, trapped and chromo-natural inflation in light of the swampland criteria and the trans-Planckian censorship conjecture

We present the first quantum field theory model of inflation that is renormalizable in the matter sector, with a super-Hubble inflaton mass and sub-Planckian field excursions, which is thus technically natural and consistent with a high-energy completion within a theory of quantum gravity. This is done in the framework of warm inflation, where we show, for the first time, that strong dissipation can fully sustain a slow-roll trajectory with slow-roll parameters larger than unity in a way that is both theoretically and observationally consistent. The inflaton field corresponds to the relative phase between two complex scalar fields that collectively break a <math><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo></math> gauge symmetry, and dissipates its energy into scalar degrees of freedom in the warm cosmic heat bath. A discrete interchange symmetry protects the inflaton mass from large thermal corrections. We further show that the dissipation coefficient decreases with temperature in certain parametric regimes, which prevents a large growth of thermal inflaton fluctuations. We find, in particular, a very good agreement with the Planck legacy data for a simple quadratic inflaton potential, predicting a low tensor-to-scalar ratio <math><mi>r</mi><mo>≲</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>.

Spain

Mar Bastero-Gil

Rudnei O. Ramos

Portugal

João G. Rosa

Towards a reliable effective field theory of inflation

Motivated by the old trans-Planckian (TP) problem of inflationary cosmology, it has been conjectured that any consistent effective field theory should keep TP modes ‘hidden’ behind the Hubble horizon, so as to prevent them from turning classical and thereby affecting macroscopic observations. In this paper we present two arguments against the Hubble horizon being a scale of singular significance as has been put forward in the TP Censorship Conjecture (TCC). First, refinements of TCC are presented that allow for the TP modes to grow beyond the horizon while still keeping the de-Sitter conjecture valid. Second, we show that TP modes can turn classical even well within the Hubble horizon, which, as such, negates this rationale behind keeping them from crossing it. The role of TP modes is known to be less of a problem in warm inflation, because fluctuations start out usually as classical. This allows warm inflation to be more resilient to the TP problem compared to cold inflation. To understand how robust this is, we identity limits where quantum modes can affect the primordial power spectrum in one specific case.

Jaime Calderón

Role of trans-Planckian modes in cosmology

The implications of the recently proposed trans-Planckian censorship conjecture (TCC) are analyzed in the context of warm inflation. It is found that for a single-stage accelerated expansion the constraints imposed by the censorship are roughly the same as for cold inflation. Next, we study how a two-stage inflationary expansion with an intermediate radiation-dominated era can alleviate the bounds imposed by the censorship. For a demonstrative toy model we found <math><mrow><mi>r</mi><mo>&lt;</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>23</mn></mrow></msup></mrow></math>, but can be <math><mi>r</mi><mo>&lt;</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math> for a weaker form of TCC for the later stages of expansion, while still satisfying the other swampland conditions.

Jaime R. Calderón

Trans-Planckian censorship and other swampland bothers addressed in warm inflation

The escape problem is defined in the context of quantum field theory. The escape rate is explicitly derived for a scalar field governed by fluctuation-dissipation dynamics, through generalizing the standard Kramers problem. In the presence of thermal fluctuations, there is a nonvanishing probability for a classical background field to escape from the well. Different from nucleation or quantum tunneling processes, the escape problem does not require the minimum of the potential, where the field is initially located in a homogeneous configuration, to be a false vacuum. The simple and well-known related problem of the escape of a classical point particle due to random forces is first reviewed. We then discuss the difficulties associated with a well-defined formulation of an escape rate for a scalar field and how these can be overcome. A definition of the Kramers problem for a scalar field and a method to obtain the rate are provided. Finally, we discuss some of the potential applications of our results, which can range from condensed matter systems, i.e., nonrelativistic fields, to applications in high-energy physics, like for cosmological phase transitions.

Joël Mabillard

Bruno W. Mintz

Formulating the Kramers problem in field theory

We study the dynamics and observational predictions of warm inflation within a supersymmetric distributed mass model. This dissipative mechanism is well described by the interactions between the inflaton and a tower of chiral multiplets with a mass gap, such that different bosonic and fermionic fields become light as the inflaton scans the tower during inflation. We examine inflation for various mass distributions, analyzing in detail the dynamics and observational predictions. We show, in particular, that warm inflation can be consistently realized in this scenario for a broad parametric range and in excellent agreement with the Planck legacy data. Distributed mass models can be viewed as realizations of the landscape property of string theory, with the mass distributions coming from the underlying spectra of the theory, which themselves would be affected by the vacuum of the theory. We discuss the recently proposed swampland criteria for inflation models on the landscape and analyze the conditions under which they can be met within the distributed mass warm inflation scenario. We demonstrate mass distribution models with a range of consistency with the swampland criteria including cases in excellent consistency.