Journal Club

Seminar Room

Monday 29th of June, 2026

Hour: 12:00

Title: Gluon production in the Color Glass Condensate from BCFW recursion

Presented by: Diogo Costa

Ref: https://arxiv.org/abs/2605.02299

Abstract:

In the Color Glass Condensate framework, the colliding projectiles are described as classical color currents. Gluon production at leading order in the coupling is obtained from the retarded solution of the classical Yang-Mills equations, with these currents acting as sources. However, while the final gluon spectrum is gauge invariant, the classical color field A^μ from which it is obtained is gauge dependent. This makes the intermediate steps of this approach unnecessarily complicated, as some effort is spent to also determine the gauge dependent part of A^μ, which is then discarded when one calculates a gauge invariant observable.
In this work, we use a generalization of BCFW recursion applicable to off-shell gluons in order to calculate directly the gauge independent gluon production amplitude. This approach allows all manipulations to be performed in terms of gauge invariant amplitudes instead of gauge dependent Feynman diagrams, and therefore provides a gauge agnostic way to obtain the result.

Hour: 12:30

Title: Spectroscopic Supermassive Dark Star candidates

Presented by: José Miguel Martín Pérez

Ref: https://arxiv.org/abs/2505.06101

Abstract:

Dark Stars, i.e. early stars composed almost entirely of hydrogen and helium but powered by Dark Matter, could form in zero metallicity clouds located close to the center of high redshift Dark Matter halos. In 2023 three of us identified (in a PNAS work) the first three photometric Dark Star candidates: JADES-GS-z11-0, JADES-GS-z12-0, and JADES-GS-z13-0. We report here our results of a followup analysis based on available NIRSpec JWST data. We find that JADES-GS-z11-0 and JADES-GS-z-13-0 are spectroscopically consistent with a Dark Star interpretation. Moreover, we find two additional spectroscopic Dark Star candidates: JADES-GS-z14-0 and JADES-GS-z-14-1, with the former being the most distant luminous object ever observed. We furthermore identify a feature in its spectrum indicative of the smoking gun signature of Dark Stars: the He IIλ1640 absorption line. In view ALMA's recent identification of a probable OIII nebular emission line in the spectrum of JADES-GS-z14-0, the simple interpretation of this object as an isolated Dark Star is unlikely. If both spectral features survive follow-up observations it would imply a Dark Star embedded in a metal rich environment, requiring theoretical refinements of the formation of evolution of Dark Stars, which in previous studies were assumed to form in isolation, without any companions.