[RBRC seminar] Fixing Small-x: From Instabilities to a Consistent NLO Framework

by Dr Yacine Mehtar-Tani (BNL)

Thursday 23 Oct 2025, 12:30 → 14:00 US/Eastern

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

The next-to-leading order (NLO) program of high-energy QCD evolution has long been hindered by instabilities in the Balitsky–Kovchegov (BK) equation, originating from large collinear double logarithms. Proposed remedies—such as phase-space constraints on gluon emission, collinear resummations, or redefinitions of the rapidity variable—are essentially ad hoc, as they do not emerge from a consistent factorization framework valid to all orders. In this work, we resolve this issue by introducing a change of basis in the space of Color Glass Condensate (CGC) operators, which naturally incorporates a dependence on a collinear factorization scale in addition to the rapidity scale. The resulting NLO BK equations are obtained from the original formulation of Balitsky and Chirilli through the application of our rotation operator, which acts as a scheme transformation. Finally, we carry out numerical simulations of the new evolution equation and demonstrate that it remains stable up to large values of rapidity.