Finite temperature field theory for the masses
Bibliographic record
Abstract
The Standard Model of particle physics is the most successful theory ever invented by humankind.At the same time, it is fundamentally incomplete.Among other things, it does not account for dark matter, which constitutes about 85% of the matter content of the universe.Many constraints on physics beyond the Standard Model come from astrophysics and cosmology.While collider physics computations can assume that processes happen in vacuum, our universe is far from being a vacuum, and this approximation will not hold in many astrophysical environments such as stars or the early universe.In these physical settings, an accurate description requires that we take into account thermal effects generated by the hot and dense medium.The Standard Model photon is particularly affected by in-medium effects.Indeed, densities of charged particles can be high in nature, and the photon's coupling to these charged particles is big enough to maintain a high interaction rate.In particular, the photon acquires an effective mass, or self-energy, in a plasma.Furthermore, it acquires a new, longitudinal degree of freedom, in addition to the two transverse ones present in vacuum.Approximately 30 years ago, Braaten and Segel derived beautiful analytic approximations for the photon self-energy, more specifically for the longitudinal and transverse modes in a homogeneous and isotropic plasma.These expressions have since been used by many researchers in the high-energy physics phenomenology community.However, these dispersion relations are only valid in the on-shell regime, meaning for actual photons that can propagate Hugo Schrer iv Abstract through the medium for an arbitrarily high distance, or in the soft photon momentum regime.There exists no analytic approximation for the general photon self-energy, which would also be generally valid off shell, meaning for virtual photons which are intermediate states in particle physics processes and which can have any energy and momentum.In this thesis, I first review some context about the search for physics beyond the standard model using cosmology and astrophysics, and show how the photon self-energy is a central element in a particular model, the dark photon.I then review some finite temperature field theory formalism and use it to compute the general photon self-energy in a homogeneous and isotropic medium to first order in the fine-structure constant.This is a general expression in the sense that it is valid on shell and off shell for any photon energy and momentum.I derive analytic approximations for the general self-energy, and I evaluate how good they are compared to numerical computations.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".