[RBRC seminar] Bridging the Parton picture with the Color Glass Condensate

by Mr Diego Padilla (UCLA)

Thursday 9 Jul 2026, 12:30 → 14:30 US/Eastern

2-160 (https://bnl.zoomgov.com/j/1600983728?pwd=RAD7OLcqre7Ycsp6JfFp6HAnpyLxex.1)

Factorization with parton distributions and the Color Glass Condensate (CGC) effective field theory are two widely used frameworks for computing cross sections in QCD. Although these approaches are formulated in terms of different degrees of freedom — interactions between individual partons versus coherent scattering off a shockwave— there are kinematic regions where both descriptions should be applicable and therefore mutually consistent. To investigate this connection, we derive GTMDs, GPDs, TMDs, PDFs, and diffractive TMDs in the shockwave/CGC limit at leading order [1]. For PDFs and GPDs, we encounter divergences that require renormalization. Through this renormalization procedure, we obtain the finite small-x parts of these distributions for the first time and recover the corresponding collinear evolution equations. Using these PDFs and GPDs, expressed in terms of dipole amplitudes, we verify the matching between CGC scattering amplitudes and their collinear-factorization counterparts for DIS, DVCS, and DVMP  to leading order [2]. This matching is performed by taking the large-Q^2 limit on the CGC side and using the small-x expansion of the parton distributions on the collinear-factorization side. Our results establish a systematic framework for matching Parton distributions and the CGC, opening the way toward extensions beyond leading order.

[1] Shohini Bhattacharya, Chuan-Qi He, Zhong-Bo Kang, Diego Padilla, Jani Penttala, arXiv:2510.02254 [hep-ph].
[2] Shohini Bhattacharya, Chuan-Qi He, Zhong-Bo Kang, Diego Padilla, Jani Penttala, arXiv:2605.14092 [hep-ph].