REVIEW
Towards the Theory of Reheating After Inflation
High Energy Physics - Phenomenology · Submitted 30 Apr 1997 · 46 references
Pith's verdict: The paper that made preheating calculable: the parabolic-scattering recursion is sound and reproduces the numerics, with soft spots confined to the last oscillation or two and to an acknowledged μ calibration.
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Referee report
The paper
The paper claims
Reheating after inflation is not a slow one-particle-at-a-time decay but a stochastic resonance, and the authors claim it can be computed analytically even though each growing mode jumps across thousands of resonance bands within a single振荡
The reading
What carries the argument
The load-bearing device is the reduction of the mode equation near each zero of the inflaton to a universal form. Writing $X_k = a^{3/2}chi_k$ removes the Hubble friction, and near $varphi(t_j)=0$ the frequency becomes $k^2/a^2 + g^2Phi^2 m^2 (t-t_j)^2$, so with $tau = k_*(t-t_j)$ and $kappa = k/(a k_*)$, where $k_* = sqrt{g m Phi}$, one gets $d^2X/dtau^2 + (kappa^2+tau^2)X = 0$. That equation has exact parabolic-cylinder solutions, hence exact reflection and transmission amplitudes $R_k$ and $D_k$ (Eqs. 51–52), which convert into a two-by-two recursion for the Bogoliubov coefficients across one kick. Iterating the recursion gives the change in occupation number per kick, $n_k^{j+1} = e^{-pi kappa^2} + (1+2e^{-pi kappa^2})n_k^j - 2 e^{-pi kappa^2/2}sqrt{1+e^{-pi kappa^2}}sqrt{n_k^j(1+n_k^j)}sinTheta_j$. The sine term is the interference between consecutive kicks; when the phases $Theta_j$ are random, the whole band structure dissolves and what remains is a broad, phase-insensitive amplification with a resonance width $k lesssim k_*/sqrt{pi}$. This is what lets the authors replace a Mathieu stability chart, which fails here, with a single growth index and then integrate over momenta.
Extended reading notes
Core claim
The central claim is that broad parametric resonance in an expanding universe with a quadratic inflaton potential is a stochastic process, and that it is nevertheless tractable analytically. In the usual treatment each mode sits in a fixed instability band of the Mathieu equation and grows at a fixed rate. Here, the authors point out, the parameter $q = g^2Phi^2/4m^2$ falls as $t^{-2}$, so within a single oscillation a mode sweeps through order $sqrt{q}$ different bands, and the phase accumulated between successive zero-crossings of $varphi$ changes by far more than $pi$. The kicks therefore arrive with uncorrelated phases, and the occupation number $n_k$ can fall as well as rise from one kick to the next — something impossible for classical particles in a fixed background. Averaged over the randomness, the growth is still exponential, with an effective index $mu$ of order $0.1$–$0.2$ (the authors quote $mu approx 0.13$). From this they derive the duration of the first stage of preheating, the amplitude $Phi_1$ and $q_1$ at its end, the criterion $g lesssim 3times10^{-4}$ for preheating to finish before backreaction matters, the growth of the effective inflaton mass as $g n_chi/|varphi|$ (a $|varphi|$ term in the potential, not $varphi^2$), and finally a condition $g m varphi Phi gtrsim 4M^2$ under which $chi$ particles of mass $M gg m$ are copiously produced.
Load-bearing premise
Every exponential estimate rests on replacing the wildly fluctuating, phase-dependent growth index of Eq. (81) by one effective constant, $mu approx 0.13$, and then integrating $n_chi propto e^{2mu m t}$ over the entire first stage.
Editorial extensions
If this is right
- For $g lesssim 3times10^{-4}$ preheating ends while backreaction is still negligible, and the perturbative reheating calculation remains the correct description of the end of the process.
- For larger $g$ a second stage follows in which the produced $chi$ particles raise the inflaton's effective frequency, shortening each oscillation and making particle production faster rather than slower, until $q sim 1/4$.
- The variance of $chi$ can reach $sqrt{langle chi^2 rangle} sim 10^{16}$ GeV, orders of magnitude above any thermal value at the same energy density, which can restore symmetry nonthermally and seed topological defects.
- Particles with mass $M gg m$ can be produced in quantity provided $g m varphi Phi gtrsim 4M^2$; producing $M = 10m$ requires $g gtrsim 0.065$, or about $0.036$ with the relaxed criterion.
- At the end of resonance the $chi$ particles outnumber nothing: rescattering leaves roughly ten times more $varphi$ particles than $chi$ particles, so the reheating temperature is still set by the later perturbative decay of the $varphi$ remnants, not by preheating.
Reading between the lines
- If $n_k$ really obeys a log-normal distribution, the volume-averaged energy density is dominated by rare patches with anomalously large occupation rather than by the mean, so preheating would be strongly inhomogeneous on sub-horizon scales; that would be a source of non-Gaussian density perturbations and possibly of primordial black holes, which the paper only gestures at.
- The parabolic-kick formalism depends only on the behaviour of $varphi$ near its zero, so it should transfer directly to any potential where the inflaton crosses zero with a linear zero, giving a general map from $V(varphi)$ to a growth index without ever writing down a Mathieu equation.
- Because $mu$ is a random variable, the honest object is a Fokker–Planck equation for the distribution of $ln n_k$; replacing it by a single mean $mu$ will systematically underestimate the upper tail, which would push the superheavy-particle mass bound of Eq. (144) upward.
- Soft $varphi$ modes with $k ll k_*$ are indistinguishable from the coherent condensate over the timescales that matter, so 'number of inflaton particles' is not a clean observable during preheating; field variances, not occupation numbers, are probably the right bookkeeping.
Original abstract
Reheating after inflation occurs due to particle production by the oscillating inflaton field. In this paper we describe the perturbative approach to reheating, and then concentrate on effects beyond the perturbation theory. They are related to the stage of parametric resonance called preheating. It may occur in an expanding universe if the initial amplitude of oscillations of the inflaton field is large enough. We investigate a simple model of a massive inflaton field coupled to another scalar field X. Parametric resonance in this model is very broad. It occurs in a very unusual stochastic manner, which is different from the parametric resonance in the case when the expansion of the universe is neglected. Quantum fields interacting with the oscillating inflaton field experience a series of kicks which occur with phases uncorrelated to each other. We call this process stochastic resonance. We develop the theory of preheating taking into account the expansion of the universe and backreaction of produced particles, including the effects of rescattering. The process of preheating can be divided into several distinct stages. At the first stage the backreaction of created particles is not important. At the second stage backreaction increases the frequency of oscillations of the inflaton field, which makes the process even more efficient than before. Then the effects related to scattering of X-particles terminate the resonance. We calculate the density of X-particles and their quantum fluctuations with all backreaction effects taken into account. This allows us to find the range of masses and coupling constants for which one has efficient preheating. In particular, under certain conditions this process may produce particles with a mass much greater than the mass of the inflaton field.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
Reheating after inflation occurs due to particle production by the oscillating inflaton field. In this paper we describe the perturbative approach to reheating, and then concentrate on effects beyond the perturbation theory. They are related to the stage of parametric resonance called preheating. It may occur in an expanding universe if the initial amplitude of oscillations of the inflaton field is large enough. We investigate a simple model of a massive inflaton field coupled to another scalar field X. Parametric resonance in this model is very broad. It occurs in a very unusual stochastic manner, which is different from the parametric resonance in the case when the expansion of the universe is neglected. Quantum fields interacting with the oscillating inflaton field experience a series of kicks which occur with phases uncorrelated to each other. We call this process stochastic resonance. We develop the theory of preheating taking into account the expansion of the universe and backreaction of produced particles, including the effects of rescattering. The process of preheating can be divided into several distinct stages. At the first stage the backreaction of created particles is not important. At the second stage backreaction increases the frequency of oscillations of the inflaton field, which makes the process even more efficient than before. Then the effects related to scattering of X-particles terminate the resonance. We calculate the density of X-particles and their quantum fluctuations with all backreaction effects taken into account. This allows us to find the range of masses and coupling constants for which one has efficient preheating. In particular, under certain conditions this process may produce particles with a mass much greater than the mass of the inflaton field.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Reheating after inflation occurs due to particle production by the oscillating inflaton field. | background 1.00 | 0.06 | 0.03 | asserted 1.00 |
| s1 | In this paper we describe the perturbative approach to reheating, and then concentrate on effects beyond the perturbation theory. | contribution 0.88 | 0.76 | 0.04 | asserted 0.80 |
| s2 | They are related to the stage of parametric resonance called preheating. | background 0.91 | 0.11 | 0.04 | asserted 0.99 |
| s3 | It may occur in an expanding universe if the initial amplitude of oscillations of the inflaton field is large enough. | background 0.91 | 0.11 | 0.04 | hedged possibility 1.00 |
| s4 | We investigate a simple model of a massive inflaton field coupled to another scalar field X. | method 0.85 | 0.76 | 0.02 | asserted 0.97 |
| s5 | Parametric resonance in this model is very broad. | result 0.97 | 0.72 | 0.05 | asserted 1.00 |
| s6 | It occurs in a very unusual stochastic manner, which is different from the parametric resonance in the case when the expansion of the universe is neglected. | result 0.96 | 0.75 | 0.09 | asserted 1.00 |
| s7 | Quantum fields interacting with the oscillating inflaton field experience a series of kicks which occur with phases uncorrelated to each other. | result 0.71 | 0.53 | 0.06 | asserted 1.00 |
| s8 | We call this process stochastic resonance. | interpretation 0.49 | 0.83 | 0.09 | asserted 0.99 |
| s9 | We develop the theory of preheating taking into account the expansion of the universe and backreaction of produced particles, including the effects of rescattering. | contribution 0.78 | 0.94 | 0.12 | asserted 0.99 |
| s10 | The process of preheating can be divided into several distinct stages. | result 0.51 | 0.50 | 0.05 | asserted 1.00 |
| s11 | At the first stage the backreaction of created particles is not important. | result 0.73 | 0.44 | 0.03 | asserted 1.00 |
| s12 | At the second stage backreaction increases the frequency of oscillations of the inflaton field, which makes the process even more efficient than before. | result 0.81 | 0.71 | 0.09 | asserted 1.00 |
| s13 | Then the effects related to scattering of X-particles terminate the resonance. | result 0.87 | 0.42 | 0.07 | asserted 1.00 |
| s14 | We calculate the density of X-particles and their quantum fluctuations with all backreaction effects taken into account. | contribution 0.51 | 0.96 | 0.07 | asserted 1.00 |
| s15 | This allows us to find the range of masses and coupling constants for which one has efficient preheating. | result 0.83 | 0.91 | 0.17 | asserted 0.99 |
| s16 | In particular, under certain conditions this process may produce particles with a mass much greater than the mass of the inflaton field. | result 0.98 | 0.82 | 0.26 | hedged possibility 1.00 |
What was examined, and what was not
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Figures
Showing 10 of the paper's 12 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:hep-ph/9704452 by the authors.
References
How later papers used it
755 later papers cite it
11 later papers by other authors are listed below: 11 used its method or tool. 1 more paper by the same authors is listed: 1 used its method or tool.
Uses its method or tool 12 of 76 papers with this label · 1 by the same authors
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Solved its equation numerically using the leading order adiabatic expansion with modes expressed as this paper's Ansatz.
Despicable Dark Relics: generated by gravity with unconstrained masses (2018) · 1.00 · paraphrased: the licence does not allow quoting
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In order to find $a^3 n_k$ we will adopt the parametrization of Ref. [ref] ,
On the Role of Cosmological Gravitational Particle Production in Baryogenesis (2024) · CGPP for spin-0 particles · 1.00
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Used this paper's method of successive scattering matrices from preheating scenarios to find an analytic expression for the number of dark photons.
Analytic study of dark photon and gravitational wave production from axion (2020) · 1.00 · paraphrased: the licence does not allow quoting
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Returning to our discussion, in order to compute $⟨χ^2 ⟩$, we write the solution of equation [ref] in terms of Bogoliubov coefficients $α_k = α_k(t)$ and $β_k = β_k(t)$ [ref] , yielding
Preheated inflation (2025) · Background dynamics · 0.98
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Following this paper, wrote down the equation of motion of the field.
Hidden Photon and Axion Dark Matter from Symmetry Breaking (2021) · 0.98 · paraphrased: the licence does not allow quoting
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Following this paper, gave the occupation number in a given mode function.
Gravitational-Wave Mediated Preheating (2014) · 0.98 · paraphrased: the licence does not allow quoting
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Following this paper's standard procedure, obtained the equation of motion of the curvaton field.
The running curvaton (2019) · 0.98 · paraphrased: the licence does not allow quoting
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Computed the occupation number of each comoving momentum mode as given by this paper to validate its analytical estimate.
Shrinking the Warm Little Inflaton (2023) · 0.98 · paraphrased: the licence does not allow quoting
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Based its appendix on ideas and methods found in Section VII B of this paper.
Irruption of massive particle species during inflation (2014) · 0.98 · paraphrased: the licence does not allow quoting
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Following this paper, wrote an expression accounting for unknown accumulated phases of the Bogoliubov coefficients.
Preheating in the Standard Model with the Higgs-Inflaton coupled to gravity (2008) · 0.94 · paraphrased: the licence does not allow quoting
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Presented the formulation of particle production by following this paper.
Moduli Oscillation Induced by Reheating (2018) · 0.89 · paraphrased: the licence does not allow quoting
By the same authors
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Used this paper's approximation to solve the equation analytically and obtain the occupation number of created particles.
Cosmological Fluctuations from Infra-Red Cascading During Inflation (2009) (same authors) · 0.99 · paraphrased: the licence does not allow quoting
How the literature uses it
668 arXiv papers cite this in 1,296 sentences
Papers citing it · 734 sentences without a confident label
Contests it 2 papers
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This led Kofman, Linde, and Starobinsky [ref] to propose that the residual field could act as dark matter, but in fact detailed calculations [ref] show the relic abundance is far too high under standard assumptions.
Triple unification of inflation, dark matter, and dark energy using a single field · Cosmological evolution · contest 0.75
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For example, the equation should include fluctuations that are present in such systems with dissipation [ref] .
Inflationary phenomenology of quadratic gravity in the Palatini formulation · Perturbative reheating · contest 0.72
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This formula can be extended to the case where the $ψ$ particles have a bare mass, the more general result is then [ref]
Constraints on generating the primordial curvature perturbation and non-Gaussianity from instant preheating · Instant preheating · 1.00
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(See also Refs. [ref] .) Within the single-field attractor, the coupled equations of motion in Eq. ([ref]) reduce to
Preheating after Multifield Inflation with Nonminimal Couplings, I: Covariant Formalism and Attractor Behavior · Mode Expansion and Adiabatic Parameters · 0.80
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Although the quantum nature of the inflaton coherent-oscillation induced GPP has been known (e.g., see [ref] ), the present paper extends the previous ideas to graviton-mediated scattering, and to our knowledge is the first to articulate clearly and to compute analytically the quantum interference effects.
Quantum interference in gravitational particle production · Introduction · 0.84
Uses its method or tool 70 papers
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The final particle number density, at large $$ values, can be computed using the equation [ref] [equation] Substituting again $ω_k_*^2(t)≃ω_k=0^2(t)$ in the above expression we can factor out $ω_k$, and write [equation]
Quintessential inflation and nonlinear effects of the tachyonic trap mechanism · The Strongly Non-Linear Regime · 0.93
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However, we will show that implementing the backreaction under the Hartree approximation [ref] leads to $ϕ_max$ significantly smaller than $10^-11$.
Cosmology in theories with spontaneous scalarization of neutron stars · Introduction · 0.96
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Ignoring backreaction onto the trajectory while $ϕ⃗$ is close to the ESP, we can compute the number density of $χ$ particles with wave-number $k$ after the encounter, $t>t_$, to [ref] [equation] where we incorporated the subsequent dilution for $t>t_$ due to the expansion of the universe.
A Terminal Velocity on the Landscape: Particle Production near Extra Species Loci in Higher Dimensions · Particle Production near ESPs and Computation of the Terminal Velocity · 0.85
Uses its data or values 3 papers
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Typical value of $⟨χ^2⟩$ in any Hubble patch is of the order of $10^-14$ at the time of the start of preheating [ref] [ During inflation $χ$ field does not get any super-horizon perturbation.
Constraints on variations in inflaton decay rate from modulated preheating · Dynamics of fields · 0.96
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The total potential energy is equally distributed among the $𝒩$ fields and sums up to $m^2 φ_0^2/2$, where $φ_0 = 0.193$ [ref] , in line with single-field models.
On the Suppression of Parametric Resonance and the Viability of Tachyonic Preheating after Multi-Field Inflation · Implementation of LatticeEasy · 0.84
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Using expressions for $Φ(t_r)$ from [ref] , immediately after preheating ends $m_χ_i∼√(g_i) ×10^15$.
Symmetric and Asymmetric Reheating · Rescattering and other effects · 0.91
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Furthermore, the relative increase resulting from each zero-crossing is consistent with that obtained using a Bogoliubov transformation [ref] .
Preheating in Palatini Higgs inflation on the lattice · Lattice results · 0.97
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Following this approach, the growth rate was estimated in Ref. [ref] to be $μ̃=qm_aπ/4$, which differs from $μ̃=q m_a/2$ predicted by NPR [ref] .
Particle decay as asymptotic narrow parametric resonance · Introduction · 0.88
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This however leads only to minor differences as compared to the standard case [ref] as we will discuss below.
Parametric Decay of the Curvaton · The parametric resonance · 0.80
Cites it as support 11 papers
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From work in the context of inflationary reheating [ref] we know that the damping of the oscillations of $ϕ$ due to the expansion of space do not destroy the resonance.
Parametric Resonance and Backreaction Effects in Magnetogenesis from Ultralight Dark Matter · Stability of the Narrow Band Resonance · 0.98
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Since the time duration of preheating is small compared to the Hubble time scale, these assumptions are valid and self-consistent during the preheating process [ref] .
Effective Action Approach for Preheating · One-loop effective action · 0.99
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Preheating with such small coupling is not efficient [ref] , i.e. reheating has to proceed via perturbative inflaton decay as we analyzed in Sec. [ref].
Small Field Polynomial Inflation: Reheating, Radiative Stability and Lower Bound · Radiative Corrections and Stability · 0.98
Cites it as background 343 papers
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Studies of reheating in inflationary cosmology [ref] have taught us that in a dynamical space-time only the broad resonance regime with $q>1$ can lead to a significant enhancement of the generation of the $χ$ particles and of the corresponding fluctuations on super-Hubble scales.
Preheating a bouncing universe · Broad Resonance with Weak Coupling · 0.84
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Particle production can occur whenever the effective mass $m_eff$ of $χ$ becomes light [ref] , given that the coupling constant is chosen appropriately.
Preheating after Multi-field Inflation · Introduction · 0.86
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Given the shape of the potential ([ref]), very different (p)reheating mechanisms could in principle take place, from a tachyonic production in the region between the end of inflation and the inflection point [ref] , an instant preheating mechanism [ref] and a parametric resonance effect around the minimum of the potential [ref] .
Preheating in the Standard Model with the Higgs-Inflaton coupled to gravity · Reheating in the Standard Model of particle physics · 0.80
Discussion
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