REVIEW
Natural Chaotic Inflation in Supergravity
High Energy Physics - Phenomenology · Submitted 27 Apr 2000 · 18 references
Pith's verdict: The shift-symmetry mechanism is sound, and the reader's tachyon objection is a misreading: the e^K factor cancels it exactly. What's left are cosmetic errata.
T0 · AI review
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Referee report
The paper
The paper claims
A shift symmetry lets chaotic inflation survive inside supergravity, with the inflaton starting far above the Planck scale.
The reading
What carries the argument
The load-bearing device is the shift symmetry of the Kähler potential, $K = K((Phi + Phi^*)^2, X X^*)$, which removes the inflaton $phi = -i(Phi - Phi^*)/sqrt{2}$ from the dangerous $e^{K}$ factor and thereby solves the $eta$ problem — the generic supergravity tendency to give every scalar a mass of order the Hubble scale. The symmetry is then broken only by the superpotential $W = m X Phi$, which is the smallest breaking that generates a potential without producing a runaway; the smallness of $m$ is justified in 't Hooft's sense because the shift symmetry is restored as $m to 0$. The auxiliary field $X$ is the second half of the mechanism: it holds the symmetry-breaking spur and then dilutes away during inflation, leaving the inflaton's potential intact.
Extended reading notes
Core claim
The claim is that chaotic inflation arises naturally in supergravity once the inflaton's Kähler potential is protected by a Nambu-Goldstone-like shift symmetry, $Phi to Phi + i C M_G$, and the symmetry is broken only in the superpotential. The authors first show why the obvious breaking term $W = m Phi^2$ fails: with $Phi + Phi^* = 0$ the potential runs to $-infty$ as $|phi| to infty$, so inflation never starts. They replace it with $W = m X Phi$, introducing a second chiral multiplet $X$, and take $K = tfrac{1}{2}(Phi + Phi^*)^2 + X X^*$. The resulting potential, for $eta, |X| ll 1$, reduces to $V simeq tfrac{1}{2} m^2 phi^2 + m^2 |X|^2$: the standard quadratic chaotic inflation potential, with $phi$ unconstrained by the exponential factor. The $eta$ field is heavy and settles to zero, $X$ rolls to zero faster than $phi$, and the density-fluctuation amplitude $delta rho / rho simeq (1/(5 sqrt{3} pi)) , m^2 / sqrt{2} (phi^2 + X^2)$ normalized at the COBE scale gives $m simeq 10^{13}$ GeV and a spectral index $n_s simeq 0.96$. Reheating is arranged through $W = lambda X H bar{H}$, giving $T_R simeq 10^9 , text{GeV} , (lambda / 10^{-5})(m / 10^{13} text{GeV})^{1/2}$; keeping $T_R$ below the gravitino bound requires $lambda lesssim 10^{-5}$, which the authors argue is natural because $H bar{H}$ can be taken even under the model's $Z_2$.
Load-bearing premise
The construction needs a higher-order term $zeta |X|^4$ in the Kähler potential with $zeta$ negative and of moderate size, because without it the potential gives $X$ a tachyonic mass-squared of order $-m^2 phi^2$ and $X$ does not settle to zero; no symmetry in the paper fixes that coefficient or its sign.
Editorial extensions
If this is right
- The inflaton potential is the textbook quadratic form $V simeq tfrac{1}{2} m^2 phi^2$, so the model inherits all of quadratic chaotic inflation's predictions, including a spectral index near $n_s simeq 0.96$ and a tensor-to-scalar ratio in the range future CMB polarization experiments target.
- The inflaton mass is fixed rather than assumed: COBE normalization gives $m simeq 10^{13}$ GeV, a value tied directly to the observed amplitude of density perturbations.
- Reheating proceeds through the coupling $lambda X H bar{H}$, which induces $lambda m phi H bar{H}$ and yields $T_R simeq 10^9$ GeV for $lambda simeq 10^{-5}$, keeping gravitino production under control.
- The model removes the need to guess a special Kähler potential: its form is dictated by a symmetry, so the flatness of the potential beyond the Planck scale is a consequence of the symmetry rather than of tuning.
- Because the shift symmetry is only softly broken, higher-order corrections to $K$ are argued to be negligible as long as $|phi| lesssim m^{-1}$, which is exactly the initial field value the chaotic scenario requires.
Reading between the lines
- The stabilization of $X$ is the part of the construction least protected by symmetry: the paper's own potential gives $X$ a mass-squared of order $-m^2 phi^2 / 2$, i.e. tachyonic and of order the Hubble scale, so the slow-roll equation $3H dot{X} simeq -m^2 X$ holds only after a higher-order $zeta |X|^4$ term with negative $zeta$ is added; the required window on $zeta$ is a tuning that the shift s
- Because the potential is exactly quadratic in the inflaton, the model is a clean target for tensor-mode searches: a detection of $r$ at the quadratic prediction would support it, and a tight upper bound below that level would remove this realization regardless of how natural its Kähler structure is.
- The same shift-symmetry device could be applied to other large-field models, since the exponential problem is generic to any inflaton asked to exceed the Planck scale; the construction is a template, not a one-off.
- The reheating sector couples to the same field $X$ that carries the symmetry breaking, so the smallness of $lambda$ and the smallness of $m$ are logically independent suppressions; a reader should ask whether a single underlying symmetry could tie them together.
Original abstract
We propose a chaotic inflation model in supergravity. In the model the K\"ahler potential has a Nambu-Goldstone-like shift symmetry of the inflaton chiral multiplet which ensures the flatness of the inflaton potential beyond the Planck scale. We show that the chaotic inflation naturally takes place by introducing a small breaking term of the shift symmetry in the superpotential. This may open a new branch of model building for inflationary universe in the framework of supergravity.
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
We propose a chaotic inflation model in supergravity. In the model the K\"ahler potential has a Nambu-Goldstone-like shift symmetry of the inflaton chiral multiplet which ensures the flatness of the inflaton potential beyond the Planck scale. We show that the chaotic inflation naturally takes place by introducing a small breaking term of the shift symmetry in the superpotential. This may open a new branch of model building for inflationary universe in the framework of supergravity.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We propose a chaotic inflation model in supergravity. | contribution 1.00 | 0.90 | 0.13 | asserted 0.92 |
| s1 | In the model the K\"ahler potential has a Nambu-Goldstone-like shift symmetry of the inflaton chiral multiplet which ensures the flatness of the inflaton potential beyond the Planck scale. | method 0.80 | 0.56 | 0.10 | asserted 1.00 |
| s2 | We show that the chaotic inflation naturally takes place by introducing a small breaking term of the shift symmetry in the superpotential. | result 0.38 | 0.93 | 0.47 | asserted 1.00 |
| s3 | This may open a new branch of model building for inflationary universe in the framework of supergravity. | interpretation 0.94 | 0.10 | 0.21 | hedged possibility 1.00 |
What was examined, and what was not
- arXiv listing abstract v2
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- references and citing sentences
- relations to other papers
- P abstract
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References
How later papers used it
143 later papers cite it
1 later paper by other authors is listed below: 1 compared its own results with it.
Compares with it 1 of 5 papers with this label
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Said that its simple chaotic inflation model with a polynomial potential almost coincides with the model of chaotic inflation in supergravity proposed in this paper.
New models of chaotic inflation in supergravity (2010) · 0.84 · paraphrased: the licence does not allow quoting
How the literature uses it
132 arXiv papers cite this in 221 sentences
Papers citing it · 155 sentences without a confident label
Builds on it 4 papers
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There, it was shown that one can significantly generalize the model of Ref. [ref] by studying more general potentials of the functional form $K((Φ-Φ̅)^2,SS̅)$ and by introducing models with a superpotential $W = S f(Φ)$, where $f(Φ)$ is an arbitrary holomorphic function.
Chaotic inflation and supersymmetry breaking · Introduction · 0.89
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One can notice that this Kähler potential is invariant under the following transformation; [equation] This shift symmetry rather generalizes the shift symmetries proposed in [ref] , in the context of supergravity realization of the chaotic inflation and running kinetic inflation.
A New Class of Non-canonical Conformal Attractors for Multifield Inflation · Basic setup · 0.83
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We will start with a simple polynomial potential that is a generalization of the potential used in Ref. [ref] : [equation] Note that the stabilizing terms $- ζ (SS̅)^2 + γ2 SS̅ (Φ-Φ̅)^2$ was added to the potential of the model of [ref] .
General inflaton potentials in supergravity · Examples · 1.00
Uses its method or tool 2 papers
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In this review, following Refs. [ref] , we introduce the Nambu-Goldstone-like shift symmetry of the inflaton superfield $Φ$ in order to naturally realize chaotic inflation in supergravity.
Supergravity based inflation models: a review · Chaotic inflation · 0.81
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We use the approach in [ref] and introduce two “orthogonal" chiral superfields [ref] , the goldstino, $S$, and inflaton superfield, $Φ$, where we denote the scalar components of these superfields with the same letter.
Sharp turns in axion monodromy: primordial black holes and gravitational waves · Multifield axion monodromy in supergravity · 0.96
Compares with it 5 papers
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In [ref] the mass of the gravitino was vanishing.
$\alpha $-Attractors: Planck, LHC and Dark Energy · Shift Symmetry and Z, T, and $Φ$ variables · 0.90
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This problem seems generic for the canonical scalar kinetic terms in the Jordan frame supergravity[One can compare this case to the generalized chaotic inflation for the minimal Kähler potential and the superpotential $W=XS^n$ with $n$ being a natural number in Refs. [ref] where the accompanying singlet has a vanishing mass at the origin.].
Chaotic inflation in Jordan frame supergravity · The tachyonic mass problem in Jordan-frame supergravity inflation · 0.97
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Also, to bring this model closer to the notations of [ref] , we use the term $- 1/2(Φ-Φ̅)^2$ instead of the term $1/2(Φ+Φ̅)^2$ in the potential of the model of Ref. [ref] .
New models of chaotic inflation in supergravity · Chaotic inflation with a quadratic potential · 0.95
Cites it as background 48 papers
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Among many (F-term) inflation models, chaotic inflation [ref] is one of the most interesting models from this viewpoint.
Phase transition and monopole production in supergravity inflation · Introduction · 0.90
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Such a shift-symmetry has been for the first time introduced in the context of chaotic inflation in supergravity (SUGRA) [ref] .
Dynamical breaking of shift-symmetry in supergravity-based inflation · Introduction · 0.86
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Sgoldstino-less models of inflation [ref] are characterized by the presence of a nilpotent chiral superfield $S^2=0$ [ref] , i.e. the goldstino superfield, responsible for spontaneous supersymmetry breaking and another chiral superfield $Φ$ whose imaginary component (in our conventions) is the inflaton field, which exhibits a shift symmetry in order to make its potential viable for inflation [ref] .
Sgoldstino-less inflation and low energy SUSY breaking · Effective field theory for sgoldstino-less inflation · 0.98
Discussion
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