Dr Mehdi Drissi


Research Fellow in Theoretical Nuclear Physics
Ph.D. (Nuclear Physics), M.Sc. (Theoretical Physics), Dipl. Ing.
+44 (0)1483 686795
15 BB 03

Biography

Areas of specialism

Many-Body Green's functions; Spontaneous Symmetry-Breaking; Superfluidity; Effective Field Theory; Renormalisation; Neutron stars

My qualifications

2015-2018
Ph.D. (Nuclear Physics)
CEA, Université Paris-Saclay
2014-2015
M.Sc. (Theoretical Physics)
ENS Ulm
2012-2015
Diplôme d'ingénieur
Centrale-Supélec
2012-2014
B.Sc. (Fundamental Physics)
Université Paris-Saclay

In the media

19-25 May 2018
Young researchers' week
Scientific mediator
Palais de la Découverte

My publications

Publications

M. Drissi (2018). Renormalization invariance of many-body observables within pionless effective field theory
View abstract View full publication
The current paradigm to describe the nuclear interaction is within the frame of Chiral Effective Field Theory (Chiral EFT) which organizes contributions to observables in a series of decreasing importance. It happens that the leading contribution already requires to solve exactly the Schrödinger equation with a particular Hamiltonian. The same requirement is at play in pionless EFT which considers only nucleonic degrees of freedom. Such calculations are numerically intractable for A-body observables with A >> 10. One must design an additional expansion and truncation for many-body observables. In this thesis, non-perturbative approximations on the basis self-consistent Green’s function (SCGF) and on many-body perturbation theory (MBPT) are considered together with a pionless EFT. The goal of the present thesis is to investigate, in such framework, the renormalization invariance of many-body observables computed in A-body sectors with A >> 10. Hopefully the lessons learnt can be extended to Chiral EFT. Analysis of numerical calculations realized with a state-of-the-art SCGF code reveals a critical numerical approximation leading to renormalization dependent observables. A necessary fix is proposed and must be implemented before any calculations based on SCGF and EFT in the future. This emphasizes the criticality of numerical approximations for any calculation within a pionless EFT. At the same time, renormalization invariance of observables computed within MBPT is studied formally, opening the path to formulate the renormalization of a wide range of many-body truncation schemes in the future.