iiinova — where your digital self keeps evolving

Daniel Green @dangreen.bsky.social · 05/11/2025

Reminder: Effective field theory is a revolutionary development in fundamental physics that has transformed the field over the past 40 years (that also makes many verified experimental predictions). Congrats to @jfdonoghue.bsky.social !

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Daniel Green @dangreen.bsky.social · 29/08/2025

For (cosmic) neutrino mass enthusiasts: Peter Graham, Joel Meyers and I have new paper, breaking down why data prefers "negative" masses and how it might be explained with new fields and/or forces. We point to a number of measurements that would clarify the situation arxiv.org/abs/2508.20999

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Daniel Green @dangreen.bsky.social · 22/08/2025

"Putative dark matter particles with masses below around 1 MeV are not ruled out by astronomical observations" Fact check: astrophysics provides a constraint that is 20 orders of magnitude stronger than this new result.

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Daniel Green @dangreen.bsky.social · 22/03/2025

The signal that is being reported everywhere violates the null energy condition and is (theoretically) a very very unlikely interpretation. But even without that theory prior, there is way too little skepticism of their interpretation. The data is only 7 points, it could be many things

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Daniel Green @dangreen.bsky.social · 22/03/2025

There are other tensions in their data that may or may not be related but were not really investigated. E.g. the measurement of the phase shift (Neff), shows a 2.7 sigma tension with the SM (arxiv.org/abs/2412.05990). Could trade all of the DE signals for just a phase shift?

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Daniel Green @dangreen.bsky.social · 22/03/2025

DESI did not explore a long list of alternatives. Unlike Planck, DESI has only a few analyses published. Analyses by other groups allow for totally different interpretations. E.g. this nice paper (arxiv.org/abs/2503.14470) shows that decaying dark matter could work

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Daniel Green @dangreen.bsky.social · 22/03/2025

PSA: when a collaboration whose name starts with DE says they have found evidence for non-standard dark energy, the community should take that interpretation with more skepticism. DESI does not show that w0wa explains there data. Eg neutrino mass remains negative even with w0wa

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Daniel Green @dangreen.bsky.social · 31/12/2024

Dec 31 - Lower bound on primordial non-Gaussianity arxiv.org/abs/1612.00033 Cabass et al. show that inflation predicts a lower bound of equilateral NG of 0.1 x (n_s-1), 3-4 orders of magnitude below the current limits, due to gravity. The search for NG has a set range and target

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Daniel Green @dangreen.bsky.social · 30/12/2024

Shapes of NG have a natural inner product defined by the independence of their estimators (arxiv.org/abs/astro-ph...). Prior to this paper, people looked for models where the predicted 3pt function was orthogonal to previous shapes. Most were just be elements of this basis.

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Daniel Green @dangreen.bsky.social · 30/12/2024

Dec 30 - CMB Bispectrum modal decomposition arxiv.org/abs/0912.5516 Fergusson et al. define a basis of orthogonal polynomials on the space of CMB 3pt functions, vastly reducing the need to find models on which to build non-Gaussian templates. Planck bounds the first 2000 terms.

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Daniel Green @dangreen.bsky.social · 29/12/2024

Dec 29 - Dispersion Relations & EFT arxiv.org/abs/hep-ph/9... Donoghue shows how to use subtracted dispersion relations to expose the structure of EFT. Specifically, this technique precisely illustrates UV information can be traded to local contact interactions.

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Daniel Green @dangreen.bsky.social · 28/12/2024

Consistency of physical experiments, such as scattering of a weak probe or positivity of energies In physical detectors, has proven to be a useful window into strongly coupled QFTs arxiv.org/abs/0803.1467 arxiv.org/abs/1212.4103 This paper gives a very clear (first) demonstration of this strategy

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Daniel Green @dangreen.bsky.social · 28/12/2024

Dec 28 - Scattering and CFT Unitarity Bounds arxiv.org/abs/0801.1140 While officially addressing the topic of "unparticles", Grinstein et al. rederive bounds on the dimensions of operators from the unitarity of scattering a weakly coupled spectator off a strongly coupled CFT

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Daniel Green @dangreen.bsky.social · 27/12/2024

Dec 27 - Weinberg Soft Theorems from Weinberg Adiabatic Modes arxiv.org/abs/1602.05196 Mirbabayi & Simonovic show that the photon and graviton soft theorems for scattering in flat space are a consequence of physical long wavelength configurations tied to large diffs (BSM)

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Daniel Green @dangreen.bsky.social · 26/12/2024

Dec 26 - Conformal Invariance of Cosmological Correlators arxiv.org/abs/1108.0874 Creminelli shows that the structure of cosmic observables follows from conformal Ward identities. He gives simple examples at 3- and 4-points that are a starting point for more complex problems

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Daniel Green @dangreen.bsky.social · 25/12/2024

I really enjoy this paper for the level of clarity and detail given to understanding the CMB. Most discussions are only 10-20% accurate and then leave Boltzmann codes to do the rest. Peaks are cleaner than the full spectra, making them a nice bridge between theory and data.

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Daniel Green @dangreen.bsky.social · 25/12/2024

Dec 25 - CMB Peak Locations arxiv.org/abs/1603.03091 Pan et al. use (semi-)analytic methods to model the location of all the CMB peaks at the level of the Planck peak measurements in TTTEEE (<1%). Many corrections are 1-10% and thus are essential for consistency with data.

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Daniel Green @dangreen.bsky.social · 24/12/2024

Dec 24 - Cosmic Bell Inequalities arxiv.org/abs/1508.01082 Maldacena writes down a model of inflation where the statistics of certain hot and cold spots encode the outcome of a Bell-measurement. This shows that the quantum nature of inflation can survive in conventional classical observables

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Daniel Green @dangreen.bsky.social · 23/12/2024

This paper includes the derivation of the change of the 4/5 -> 16/15 factor in the diffusion damping coefficient from polarization. This was first pointed out by Kaiser but I find their treatment particularly easy to follow, perhaps because one of the authors was an undergraduate at the time

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Daniel Green @dangreen.bsky.social · 23/12/2024

Dec 23 - Analytic CMB Polarization arxiv.org/abs/astro-ph... Zaldarriaga & Harari give a thorough analytic treatment of how polarized scattering affects the evolution of the photon distribution function and the appearance of temperature and polarized CMB anisotropies

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Daniel Green @dangreen.bsky.social · 22/12/2024

These papers should be read with Polchinski's review of the CC problem arxiv.org/abs/hep-th/0... He nicely explains why this type of solution usually doesn't work: vacuum loops contribute to the mass/energy of many states and must couple to gravity universally.

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Daniel Green @dangreen.bsky.social · 22/12/2024

Dec 22 - Fat Gravitons and the CC arxiv.org/abs/hep-th/0... arxiv.org/abs/hep-th/0... Sundrum tries to construct a theory of gravity where vacuum loops don't gravitate. This theory is non-local in a non-trivial way in order to avoid the very strong equivalence principle constraints in this idea.

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Daniel Green @dangreen.bsky.social · 21/12/2024

Ruling out this idea was a key motivation for the initial work on the conformal bootstrap arxiv.org/abs/0807.0004 This program has had much broader applications in understanding CFTs. However, the original idea is still interesting, particularly for models with weakly broken conformal invariance.

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Daniel Green @dangreen.bsky.social · 21/12/2024

Dec 21 - Conformal Technicolor arxiv.org/abs/hep-ph/0... Luty & Okui rephrase the hierarchy problem as a statement about the relationship between the dimensions of operators. The idea is that the Higgs has a dimension near 1 but all the operators in its OPE have dimensions > 4.

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Daniel Green @dangreen.bsky.social · 20/12/2024

Dec 20 - Spontaneously broken spacetime symmetries arxiv.org/abs/hep-th/0... Low & Manohar explain why there are often fewer Goldstone modes than broken generators for spacetime symmetries. A goldstone acts like a local symmetry, which is not unique to a single global generator.

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Daniel Green @dangreen.bsky.social · 19/12/2024

McDonald and Roy also give this fantastic explanation for why you should care about this subject: every mode costs about $1000 so even a small improvement in modeling translates into Billions of $ in modes. I regularly use this argument for explaining the value of theory.

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Daniel Green @dangreen.bsky.social · 19/12/2024

Dec 19 - Renormalizing Bias Parameters arxiv.org/abs/astro-ph... arxiv.org/pdf/0902.0991 McDonald (+ Roy) show how describing the statistics of tracers of dark matter (such as galaxies) requires renormalization of the bias parameters. They anticipate/discover the EFT structure found later.

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Daniel Green @dangreen.bsky.social · 18/12/2024

Dec 18 - Indirect Evidence for Quantum Gravity journals.aps.org/prl/abstract... Page and Geilker design and perform an experiment to test if gravity is only (semi-) classical. They test and exclude the hypothesis that gravity is classical but couples to the quantum averaged stress tensor of matter

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Daniel Green @dangreen.bsky.social · 17/12/2024

Positivity bounds has become a huge subject following Adams et al, but in the meantime Pham and Truong's paper was mostly forgotten. In '85, EFT thinking hadn't really taken hold, perhaps making this less significant. But the people developing EFTs in the 90s knew this paper

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Daniel Green @dangreen.bsky.social · 17/12/2024

Dec 17 - Positivity Bounds journals.aps.org/prd/abstract... In 1985, Pham and Truong use dispersion relations to show that the 4 derivative term in pi-pi scattering must be positive. This was rediscovered (and generalized) 20 years later by Adams et al (arxiv.org/abs/hep-th/0...).

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Daniel Green @dangreen.bsky.social · 16/12/2024

100s of papers have been written recently on the 4 point function in the context of the cosmological bootstrap and cosmological collider. It is a window into extraordinarily interesting physics. Yet, these papers are the best measurements and have 59 and 7 citations respectively.

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Daniel Green @dangreen.bsky.social · 16/12/2024

Dec 16 - CMB Trispectrum constraints arxiv.org/abs/2205.14408 arxiv.org/abs/1502.00635 These papers place the best constraints on primordial 4-point functions using Planck CMB data. Planck explored 3-point functions is great detail but analyses at higher points have been limited.

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Daniel Green @dangreen.bsky.social · 15/12/2024

Dec 15 - Scattering amplitudes and Navier-Stokes arxiv.org/abs/2010.15970 www.sciencedirect.com/science/arti... Cheung & Mangan (building on an old paper by Wyld) study fluid dynamics through the lens of scattering amplitudes. They find new structures in fluids, particularly the double-copy

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Daniel Green @dangreen.bsky.social · 14/12/2024

Solvable toy models haven't been valued in cosmology the way they are in QFT or Stat Mech. Yet, this paper shows explicitly how EFT works compared to previous approaches to perturbation theory. In 3+1d, this was (and is) much debated but in 1+1d you can just calculate and check.

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Daniel Green @dangreen.bsky.social · 14/12/2024

Dec 14 - cosmological perturbation theory in 1+1 D arxiv.org/abs/1502.07389 McQuinn and White study the evolution of structure in 1+1 dimensions, where the all-loop results can be calculated. They show SPT has a finite radius of convergence but doesn't converge to simulations.

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Daniel Green @dangreen.bsky.social · 13/12/2024

Dec 13 - RG flow between minimal models inspirehep.net/literature/2... Zamolodchikov uses conformal perturbation theory to calculate the flow from the p to p-1 minimal model. He shows how to reproduce the predictions for the IR dimensions at p-1 from the data of the UV fixed point.

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Daniel Green @dangreen.bsky.social · 12/12/2024

This paper is technical but offers a really interesting window into asymptotic observables beyond the S-matrix in flat space. Although it fails for quantum gravity, due to back reaction, it is likely have lessons to teach us about QFT in dS (much like arxiv.org/abs/2308.02125)

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Daniel Green @dangreen.bsky.social · 12/12/2024

Dec 12 - A de Sitter S-matrix arxiv.org/abs/1209.6039 Marolf et al. define an S-matrix for massive particles in (fixed) global dS. They prove that many facts about flat space S-matrix also apply to dS. They develop a lot of interesting ideas that should have a wide range of applications

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Daniel Green @dangreen.bsky.social · 11/12/2024

Infinite volumes and large metric fluctuations severely limit our rigorous understanding of eternal inflation. The phase transition approaches the problem from the calculable regime offering real insights, including implications for the NEC, dS entropy, etc (based on arxiv.org/abs/0704.1814)

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Daniel Green @dangreen.bsky.social · 11/12/2024

Dec 11 - The Phase Transition to Eternal Inflation arxiv.org/abs/0802.1067 Creminelli et al define the transition to slow-roll eternal inflation by the diverging volume of the reheating surface. They offer a precise prediction for the amplitude of the power spectrum where this occurs.

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Daniel Green @dangreen.bsky.social · 10/12/2024

Physical detectors are important for making sense of a variety of analytic results from QFT in curved space. This paper develops a precise way to seeing the role of the detector through explicit calculations. Forgotten for 30 years, this idea has recently found broader traction.

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Daniel Green @dangreen.bsky.social · 10/12/2024

Dec 10 - Detectors and Rindler Particles journals.aps.org/prd/abstract... Unruh and Wald give a fantastically clear explanation of why accelerating observers see a thermal spectrum of particles: the particles are created from the energy you put into the detector to accelerate it.

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Daniel Green @dangreen.bsky.social · 09/12/2024

This paper is by serious astrophysicists with a lot of experience with these kinds of cooling curves. However, this paper has not found traction in the particle physics community, where the earlier result is still often shown as a WD cooling hint (eg arxiv.org/pdf/1602.00039)

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Daniel Green @dangreen.bsky.social · 09/12/2024

Dec 9 - Axion-electron coupling limit from 47 Tucanae arxiv.org/abs/1507.05665 Studying white dwarf cooling in this globular cluster, Hansen et al. bound the axion coupling g_ae < 8.4E-14. This excludes the hint of axion cooling seen in previous studies (eg arxiv.org/abs/0806.2807).

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Daniel Green @dangreen.bsky.social · 08/12/2024

Dec 8 - EFT / model building and the anomalous perihelion of mercury arxiv.org/abs/1106.1568 Wells explores how a model building / EFT approach to explaining Mercury's orbit would have worked. He introduces 3 ideas that all can work, and are realized in GR in different gauges.

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Daniel Green @dangreen.bsky.social · 07/12/2024

Despite being landmark results (and featured in my '22 twitter list), these papers are not cited and likely not on the radar of most younger physicists. But if you ask people who were around at the time, they say Boomerang and the subsequent analyses were really the pivotal moment for the field.

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Daniel Green @dangreen.bsky.social · 07/12/2024

This is one of the great scientific achievements of the past 30 years. Building on the analysis techniques of BOOMERANG arxiv.org/abs/astro-ph... and combining multiple data sets, they reach modern precision before WMAP's first release. Prior measurements of the age varied from 8-18 billion years

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Daniel Green @dangreen.bsky.social · 07/12/2024

Dec 7 - The Age of the Universe arxiv.org/abs/astro-ph... Combining data from CBI, DASI, BOOMERANG ++, Seivers et al. measure the age to be 13.7 +/- 0.2 billion years in near perfect agreement the modern value. This is when cosmology becomes a precision subject, giving tight errors on LCDM.

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Daniel Green @dangreen.bsky.social · 06/12/2024

Dec 6 - Coherent Phase Argument for Inflation arxiv.org/abs/hep-ph/0... The horizon problem in the era of precision CMB is better understood in terms of the fact that all sound waves have the same phase. Dodelson provides a simple and powerful explanation of this modern argument.

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Daniel Green @dangreen.bsky.social · 05/12/2024

Thanks for the reference! I knew the paper, but had forgotten this analysis. Looking at it again, the summary plots are not are maybe a bit worrying?

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