What is the Current Status and Future Perspective on Low's Soft-Photon Puzzle?

[kodama]

TL;DR

the long-standing discrepancy between experimental data and predictions based on Low’s soft-photon theorem

Physics Reports
Volume 1097, 18 December 2024, Pages 1-40

Anomalous soft photons: Status and perspectives​

Anomalous soft photons: Status and perspectives​

Author links open overlay panelR. Bailhache
Abstract
This report summarizes the work of the EMMI Rapid Reaction Task Force on “Real and Virtual Photon Production at Ultra-Low Transverse Momentum and Low Mass at the LHC”. We provide an overview of the soft-photon puzzle, i.e., of the long-standing discrepancy between experimental data and predictions based on Low’s soft-photon theorem, also referred to as “anomalous” soft photon production, and we review the current theoretical understanding of soft radiation and soft theorems. We also focus on low-mass dileptons as a tool for determining the electrical conductivity of the medium produced in high-energy nucleus–nucleus collisions. We discuss how both topics can be addressed with the planned ALICE 3 detector at the LHC.
https://www.sciencedirect.com/science/article/pii/S0370157324003478?via=ihub

are there any explanation for soft-photon puzzle?

is “anomalous” soft photon production evidence for dark matter, perhaps decay of dark matter gives rise to excited soft-photon?

 

[mitchell porter]

Soft photons are very-low-energy photons. The low energy means that a single interaction can emit large numbers of them. There are various theorems (soft pion theorem, soft photon theorem, soft graviton theorem), all due to Weinberg I think, which describe how scattering amplitudes change, as the number of outgoing soft particles increases. These theorems are related to new symmetries "at infinity", since you are changing the asymptotic state by adding the soft particles. Stephen Hawking's last coauthored papers, about "soft hair" on black holes, propose that black holes carry a soft charge which shows up in the soft component of the Hawking radiation.

I have never heard of this "puzzle" before. But it is not something I would expect to be resolved by new fundamental particles, since the soft emissions are governed by these theorems regardless of what the specific fields are. I assume it's just a matter of an error in calculation, like the use of a wrong approximation. That seems to be what this 2023 paper says.

 

[kodama]

Soft photons are very-low-energy photons. The low energy means that a single interaction can emit large numbers of them. There are various theorems (soft pion theorem, soft photon theorem, soft graviton theorem), all due to Weinberg I think, which describe how scattering amplitudes change, as the number of outgoing soft particles increases. These theorems are related to new symmetries "at infinity", since you are changing the asymptotic state by adding the soft particles. Stephen Hawking's last coauthored papers, about "soft hair" on black holes, propose that black holes carry a soft charge which shows up in the soft component of the Hawking radiation.

I have never heard of this "puzzle" before. But it is not something I would expect to be resolved by new fundamental particles, since the soft emissions are governed by these theorems regardless of what the specific fields are. I assume it's just a matter of an error in calculation, like the use of a wrong approximation. That seems to be what this 2023 paper says.

[Submitted on 7 Dec 2022 (v1), last revised 18 Dec 2022 (this version, v2)]
The Low theorem for diffractive bremsstrahlung and the soft photon puzzle
B. Z. Kopeliovich, I. K. Potashnikova, Ivan Schmidt

The anomalous excess of small-kT photons radiated along with multi-hadron production, is challenging the physics community over four decades, but no solution has been proposed so far.

https://doi.org/10.48550/arXiv.2212.03424

 

[kodama]

Soft photons are very-low-energy photons. The low energy means that a single interaction can emit large numbers of them. There are various theorems (soft pion theorem, soft photon theorem, soft graviton theorem), all due to Weinberg I think, which describe how scattering amplitudes change, as the number of outgoing soft particles increases. These theorems are related to new symmetries "at infinity", since you are changing the asymptotic state by adding the soft particles. Stephen Hawking's last coauthored papers, about "soft hair" on black holes, propose that black holes carry a soft charge which shows up in the soft component of the Hawking radiation.

I have never heard of this "puzzle" before. But it is not something I would expect to be resolved by new fundamental particles, since the soft emissions are governed by these theorems regardless of what the specific fields are. I assume it's just a matter of an error in calculation, like the use of a wrong approximation. That seems to be what this 2023 paper says.

Abstract​

It is proposed to improve the agreement with experimental data in comparison with the previous works for the soft photon spectrum as a function of the transverse momentum in

collisions with an incident proton momentum of 450 GeV/ in order to clearly isolate the signal on the detection of the X17 boson.

D’yachenko, A.T. On the Possible Detection of New Particles as Candidates for the Role of Dark Matter Particles. Phys. Part. Nuclei 56, 772–776 (2025). https://doi.org/10.1134/S1063779624702277