Daniel Green
@dangreen.bsky.social
Associate Professor @UCSanDiego, particle theory and cosmology
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 !
Congrats to @jfdonoghue.bsky.social !
November 5, 2025 at 7:49 PM
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 !
Congrats to @jfdonoghue.bsky.social !
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
arxiv.org/abs/2508.20999
August 29, 2025 at 2:59 AM
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
arxiv.org/abs/2508.20999
"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.
Fact check: astrophysics provides a constraint that is 20 orders of magnitude stronger than this new result.
August 22, 2025 at 4:29 PM
"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.
Fact check: astrophysics provides a constraint that is 20 orders of magnitude stronger than this new result.
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
March 22, 2025 at 6:35 PM
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
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?
March 22, 2025 at 6:35 PM
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?
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
March 22, 2025 at 6:35 PM
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
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
DESI does not show that w0wa explains there data. Eg neutrino mass remains negative even with w0wa
March 22, 2025 at 6:35 PM
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
DESI does not show that w0wa explains there data. Eg neutrino mass remains negative even with w0wa
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
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
December 31, 2024 at 8:37 AM
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
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
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.
December 30, 2024 at 8:39 AM
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.
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.
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.
December 30, 2024 at 8:39 AM
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.
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.
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.
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.
December 29, 2024 at 9:02 AM
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.
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.
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
arxiv.org/abs/0803.1467
arxiv.org/abs/1212.4103
This paper gives a very clear (first) demonstration of this strategy
December 28, 2024 at 8:51 AM
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
arxiv.org/abs/0803.1467
arxiv.org/abs/1212.4103
This paper gives a very clear (first) demonstration of this strategy
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
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
December 28, 2024 at 8:51 AM
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
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
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)
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)
December 27, 2024 at 7:37 AM
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)
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)
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
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
December 26, 2024 at 6:29 AM
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
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
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.
December 25, 2024 at 4:50 AM
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.
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.
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.
December 25, 2024 at 4:50 AM
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.
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.
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
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
December 24, 2024 at 6:19 AM
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
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
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
December 23, 2024 at 5:43 AM
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
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
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
December 23, 2024 at 5:43 AM
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
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
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.
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.
December 22, 2024 at 6:08 AM
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.
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.
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.
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.
December 22, 2024 at 6:08 AM
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.
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.
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.
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.
December 21, 2024 at 8:10 AM
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.
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.
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.
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.
December 21, 2024 at 8:10 AM
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.
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.
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.
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.
December 20, 2024 at 8:26 AM
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.
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.