I Low’s soft-photon puzzle

  • I
  • Thread starter Thread starter kodama
  • Start date Start date
kodama
Messages
1,074
Reaction score
144
TL;DR Summary
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?
 
Last edited:
Physics news on Phys.org
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.
 
  • Like
Likes ohwilleke and kodama
mitchell porter said:
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.

 
mitchell porter said:
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
 
https://arxiv.org/pdf/2503.09804 From the abstract: ... Our derivation uses both EE and the Newtonian approximation of EE in Part I, to describe semi-classically in Part II the advection of DM, created at the level of the universe, into galaxies and clusters thereof. This advection happens proportional with their own classically generated gravitational field g, due to self-interaction of the gravitational field. It is based on the universal formula ρD =λgg′2 for the densityρ D of DM...
Many of us have heard of "twistors", arguably Roger Penrose's biggest contribution to theoretical physics. Twistor space is a space which maps nonlocally onto physical space-time; in particular, lightlike structures in space-time, like null lines and light cones, become much more "local" in twistor space. For various reasons, Penrose thought that twistor space was possibly a more fundamental arena for theoretical physics than space-time, and for many years he and a hardy band of mostly...
Back
Top