REVIEW
Low reheating temperature and the visible sterile neutrino
Astrophysics · Submitted 13 Mar 2004 · 37 references
Pith's verdict: One clean idea — sterile abundance scaling as T_R^3 and independent of m_s — that holds up, with only minor unquantified systematics in the normalization.
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Referee report
The paper
The paper claims
A low reheating temperature after inflation would let sterile neutrinos mix with ordinary neutrinos as strongly as experiments allow, because the sterile abundance shrinks with the cube of the reheating temperature.
The reading
What carries the argument
The load-bearing object is the sterile neutrino distribution function inherited from the Dodelson-Widrow production calculation, truncated at the reheating temperature. In the standard treatment the sterile abundance is built up by active-to-sterile conversion over a wide temperature range and ends up tied to a very small mixing angle; here the conversion starts only at $T_R$, so the distribution is the equilibrium Fermi-Dirac form multiplied by a factor $3.2 d_alpha (T_R/5~MeV)^3 sin^2 2theta (E/T)$, with $d_alpha = 1.13$ for electron neutrinos and $0.79$ for muon and tau neutrinos. That single factor carries the whole argument: it converts a constraint on mixing into a constraint on reheating temperature, and it makes the relic density linear in $m_s$ and in $sin^2 2theta$ but cubic in $T_R$. The authors also flag where their own bound is incomplete: the diffuse-photon bound on radiative decays is computed for unclustered neutrinos, while the sterile neutrinos heavier than about 100 eV would be gravitationally clustered, and they state that the estimate of the clustered contribution is missing in the literature.
Extended reading notes
Core claim
The paper's claim is that the cosmological bound on active-sterile neutrino mixing is not a fixed wall but a function of the reheating temperature at the end of inflation. Following the Dodelson-Widrow calculation, sterile neutrinos are produced mainly at $T_{max} = 133 (m_s/1~keV)^{1/3}$ MeV; if $T_R < T_{max}$ the production is cut off, and the sterile distribution function becomes a simple rescaling of the active one, $f_s(E,T) = 3.2 d_alpha (T_R/5~MeV)^3 sin^2 2theta (E/T) f_alpha(E,T)$. The sterile-to-active number ratio is then $f = 10 d_alpha sin^2 2theta (T_R/5~MeV)^3$, and the relic density is $Omega_s h^2 = 0.1 d_alpha (sin^2 2theta/10^{-3})(m_s/1~keV)(T_R/5~MeV)^3$. Because the abundance depends on the mixing angle and the reheating temperature but not separately on the sterile mass, a low $T_R$ buys freedom in the mixing angle. The authors then map the surviving parameter space for $nu_e to nu_s$ and $nu_mu,tau to nu_s$ against supernova 1987A energy-loss bounds, radiative-decay bounds from the Solar Maximum Mission and the diffuse extragalactic photon background, CMB spectral distortions, big bang nucleosynthesis limits on extra radiation, the hot-dark-matter sum-of-masses bound, and the reactor, accelerator, $\beta$-decay and neutrinoless double $\beta$ decay limits. They conclude that sterile neutrinos in this scenario are viable hot dark matter candidates, that the LSND-motivated sterile neutrino is allowed, and that future experiments could see a mixing as large as $sin^2 2theta$ of order $10^{-3}$ to $10^{-1}$.
Load-bearing premise
The calculation assumes that at the reheating temperature the ordinary neutrinos already follow a standard thermal equilibrium distribution, which is why the authors restrict themselves to $T_R ge 5$ MeV and to a negligible primordial lepton asymmetry; if the active neutrinos arrive with a different spectrum or a large asymmetry, the simple $T_R^3$ rescaling of the Dodelson-Widrow result and the allowed regions drawn from it both change.
Editorial extensions
If this is right
- A sterile neutrino with mass and mixing in the LSND-favoured region, which would overclose the universe under standard assumptions, becomes cosmologically allowed if the reheating temperature is around 5 MeV.
- The allowed region of the $m_s$-$sin^2 2theta$ plane for both electron and muon/tau flavours extends to mixing angles set by laboratory and supernova bounds rather than by relic abundance, so future disappearance and neutrinoless double beta decay experiments have a real target.
- Sterile neutrinos with masses of order 0.1 to a few keV remain viable hot dark matter candidates, while masses above about 1 keV are disfavoured by supernova cooling and radiative decay bounds.
- A confirmed sterile neutrino in the reopened window would imply an unusual cosmology, with baryogenesis proceeding through a mechanism such as Affleck-Dine and the bulk of the dark matter made of something other than thermally produced particles.
Reading between the lines
- The suppression mechanism is generic to any relic that freezes in through mixing above the reheating temperature, so the same argument should reopen mixing windows for other feebly coupled particles, not just sterile neutrinos.
- Because the scenario requires a low reheating temperature, it is in tension with standard thermal leptogenesis; a future independent determination of the baryogenesis route would therefore either support or close this window without any neutrino experiment being performed.
- The sterile spectrum here is a rescaled equilibrium distribution rather than the Dodelson-Widrow non-thermal shape, and the authors note their neutrinos are hotter than those in the structure-formation reference they cite, so the warm-dark-matter mass limit quoted for the standard case should be recomputed for this scenario rather than borrowed.
- Precision measurements of the effective number of relativistic species and of the sum of neutrino masses, from the cosmic microwave background and from large-scale structure, are the natural place to look for a low reheating temperature, since they constrain the same $T_R$ that controls the sterile abundance.
Original abstract
We present here a scenario, based on a low reheating temperature T_R << 100 MeV at the end of (the last episode of) inflation, in which the coupling of sterile neutrinos to active neutrinos can be as large as experimental bounds permit (thus making this neutrino ``visible'' in future experiments). In previous models this coupling was forced to be very small to prevent a cosmological overabundance of sterile neutrinos. Here the abundance depends on how low the reheating temperature is. For example, the sterile neutrino required by the LSND result does not have any cosmological problem within our scenario.
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 present here a scenario, based on a low reheating temperature T_R << 100 MeV at the end of (the last episode of) inflation, in which the coupling of sterile neutrinos to active neutrinos can be as large as experimental bounds permit (thus making this neutrino ``visible'' in future experiments). In previous models this coupling was forced to be very small to prevent a cosmological overabundance of sterile neutrinos. Here the abundance depends on how low the reheating temperature is. For example, the sterile neutrino required by the LSND result does not have any cosmological problem within our scenario.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We present here a scenario, based on a low reheating temperature T_R << 100 MeV at the end of (the last episode of) inflation, in which the coupling of sterile neutrinos to active neutrinos can be as large as experimental bounds permit (thus making this neutrino ``visible'' in future experiments). | contribution 1.00 | 0.85 | 0.82 | asserted 0.58 |
| s1 | In previous models this coupling was forced to be very small to prevent a cosmological overabundance of sterile neutrinos. | background 0.96 | 0.03 | 0.05 | asserted 1.00 |
| s2 | Here the abundance depends on how low the reheating temperature is. | interpretation 0.30 | 0.51 | 0.10 | asserted 1.00 |
| s3 | For example, the sterile neutrino required by the LSND result does not have any cosmological problem within our scenario. | result 0.62 | 0.72 | 0.18 | asserted 0.97 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Figures reproduced from arXiv:astro-ph/0403323 by the authors.
References
How later papers used it
56 later papers cite it
3 papers by the same authors are listed below: 3 built on it.
Builds on it 3 papers · 3 by the same authors
By the same authors
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Concentrated on the production of massive (mostly sterile) neutrinos heavier than 1 MeV through the conversion of active neutrinos for T_RH < m_s, having already applied the same ideas to lighter sterile neutrinos in this paper.
MeV sterile neutrinos in low reheating temperature cosmological scenarios (2008) (same authors) · 0.98 · paraphrased: the licence does not allow quoting
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Updated the older constraints of this paper, extended the results of another work by pointing out the significance of upcoming laboratory experiments, and extended another work's analysis of keV-mass neutrinos down to 0.01 eV masses.
Cosmological Dependence of Non-resonantly Produced Sterile Neutrinos (2019) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
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Extended another work's previous LRT analysis focusing on keV-mass neutrinos down to 0.01 eV masses and updated the older constraints of this paper.
Visible Sterile Neutrinos as the Earliest Relic Probes of Cosmology (2019) (same authors) · 1.00 · paraphrased: the licence does not allow quoting
How the literature uses it
52 arXiv papers cite this in 88 sentences
Papers whose main result relates to this one's
States the same result 1 paper
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Thus, in this case cosmological bounds become much less stringent than usually assumed, allowing sterile neutrinos to be ``visible'' in future experiments.
MeV sterile neutrinos in low reheating temperature cosmological scenarios · 0.96
Papers citing it · 63 sentences without a confident label
Contests it 1 paper
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Note that this result is at odds with [ref] , where it was assumed that the production of sterile neutrinos starts at $$.
Sterile neutrino production in models with low reheating temperatures · Sterile neutrino production in oscillations · contest 0.85
Builds on it 3 papers
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We concentrate here on the production of massive (mostly sterile) neutrinos heavier than 1 MeV through the conversion of active neutrinos for $T_RH < m_s$, having already applied the same ideas to lighter sterile neutrinos [ref] .
MeV sterile neutrinos in low reheating temperature cosmological scenarios · Introduction · 0.98
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We extend the results of the previous LRT analysis focusing on keV-mass neutrinos of [ref] down to 0.01 eV masses and update the older constraints of [ref] .
Visible Sterile Neutrinos as the Earliest Relic Probes of Cosmology · Introduction · 1.00
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We update the older constraints of Ref. [ref] , extend the results of Ref. [ref] – pointing out the significance of upcoming laboratory experiments, and extend the analysis of Ref. [ref] on keV-mass neutrinos down to 0.01 eV masses.
Cosmological Dependence of Non-resonantly Produced Sterile Neutrinos · Introduction · 1.00
Compares with it 2 papers
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For comparison, we also reconsider low reheating temperature models [ref] , in which entropy is produced and the radiation bath is subdominant during the non-standard phase.
Cosmological Dependence of Non-resonantly Produced Sterile Neutrinos · Introduction · 1.00
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which is consistent with the previous studies with simplified treatments [ref] .
MeV-scale reheating temperature and cosmological production of light sterile neutrinos · Constraints from CMB · 0.95
Cites it as support 1 paper
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Therefore, keV-scale sterile neutrinos are still subject to cosmological constraints at the largest mixing angles [ref] .
Visible in the laboratory and invisible in cosmology: decaying sterile neutrinos · Neutrinos in a Low-Reheating Temperature Universe · 0.98
Cites it as background 16 papers
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Several scenarios have been proposed as the suppression mechanism: large chemical potentials of active neutrinos [ref] , self-interaction or non-standard interaction of sterile neutrinos [ref] , or low reheating temperature of the Universe [ref] .
MeV-scale reheating temperature and cosmological production of light sterile neutrinos · Introduction · 0.84
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Sterile neutrinos may also play the role of the dark matter, e.g., [ref] and affect a host of interesting cosmological and astrophysical processes, including the production of baryon [ref] and lepton [ref] asymmetries, Big Bang Nucleosynthesis [ref] , the evolution of the matter power spectrum [ref] , reionization [ref] , neutrino oscillations [ref] , pulsar kicks [ref] , and supernovae [ref] .
Constraining Sterile Neutrino Warm Dark Matter with Chandra Observations of the Andromeda Galaxy · Introduction · 0.95
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Several related studies have been previously carried out [ref] .
Cosmological Dependence of Non-resonantly Produced Sterile Neutrinos · Introduction · 0.89
Discussion
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