LPTMC Seminars
The seminars take place in room 523, corridor 12-13, 5th floor.
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[Séminaire FRG] Nicolás Wschebor (Univ. Montevideo)
01.10.2026 14:00 - 15:30Séminaires FRGSalle 523, couloir 12-13, 5è étage01.10.2026 14:00 - 15:30[Séminaires FRG][Séminaire FRG] Nicolás Wschebor (Univ. Montevideo)Is the stability matrix of the FRG flow around a fixed point self-adjoint?
Abstract: In unitary...
Is the stability matrix of the FRG flow around a fixed point self-adjoint?
Abstract: In unitary conformal field theories, it has been shown that the spectrum of scaling dimensions is real and bounded from above. FRG analysis always reveals a discrete spectrum with real parts bounded from above, but complex eigenvalues are often obtained. The aim of this talk, which relates to ongoing work, is to analyse the extent to which these complex values are physical or spurious. We will review the main characteristics of the spectrum obtained in the Derivative Expansion of the FRG. We will then analyse whether the results obtained in unitary conformal field theories are consistent with these findings. Finally, we will prove that the LPA equation for any scalar theory with a real fixed point potential has a stability matrix operator which, when combined with an appropriate scalar product, is self-adjoint. This implies that, for eigenperturbations with bounded norm, have eigenvalues which form a discrete and real spectrum in LPA approximation (for real fixed points). Finally, we will discuss the extent to which this result can be generalised to more complex approximations.
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Mike Chatzittofi (DAMTP, Cambridge)
29.09.2026 10:45 - 11:45SéminairesSalle 523, couloir 12-13, 5è étage29.09.2026 10:45 - 11:45[Séminaires]Mike Chatzittofi (DAMTP, Cambridge)Nonequilibrium nucleation theory for nonconserved fields: from active matter to population...
Nonequilibrium nucleation theory for nonconserved fields: from active matter to population dynamics
Classical nucleation theory (CNT) describes the formation of a stable phase from a metastable one. In equilibrium systems, it quantifies the free-energy competition between a favorable bulk gain and an unfavorable interfacial cost. For systems without detailed balance, the corresponding nonequilibrium nucleation theory (NNT) was so far developed only for cases with a conserved order parameter, such as active fluid-fluid phase separation. Here we construct the NNT for systems with a (single, scalar) nonconserved order parameter. Unlike in the conserved case, the nucleation barrier controlling (noise-driven) droplet growth is profoundly altered by deviations in the interfacial density profile from the one arising during (deterministic) droplet relaxation. The barrier can nonetheless be analysed by carefully defining the reaction coordinate (droplet radius) to project out those deviations. We give explicit NNT predictions for models drawn from population dynamics and active matter, finding excellent agreement with numerical studies.