# Particles, Astroparticles, Cosmology: Theory

Manager: **Julien LAVALLE**

###### Summary

# Research Topics

Ours activities are spanning various domains, from formal subjects in field theory to theoretical and phenomenological topics linked to current experiments in high-energy collider particle physics (e.g. LHC), or experiments in astroparticle and cosmology (Fermi, AMS, Planck, XENON, LUX, etc.).

One may describe those activities along the following sub-topics :

**Theory and phenomenology beyond the Standard Model :**

Minimal Supersymmetric Standard Model (MSSM) or its extension with a singlet (NMSSM) ; supersymmetry breaking models (super-gravity, AMSB, GMSB) ; development of codes dedicated to the computation of super-particle spectra (SuSpect, NMSSMTools) ; Grand Unification (GUT) models ; flavor physics (neutrinos, leptogenesis) ; composite models ; phenomenology at colliders and complementarity with dark matter searches.

**Astroparticle Physics :**

supersymmetric dark matter candidates (neutralinos, gravitinos, singlinos) or others (e.g. composite models) ; generic relic density calculations (WIMPs, FIMPs, etc.) ; theoretical analyses for direct and indirect searches, study of collider signatures and complementarities ; constraints from Big Bang Nucleosynthesis (BBN) ; phenomenology of Galactic cosmic rays (diffusive transport and interactions) ; high-energy antimatter cosmic rays (positrons, antiprotons) ; local astrophysical sources of positrons ; dark matter subhalos and CDM small-scale issues ; structure formation ; galactic dynamics and DM phase space.

NB : the 2 above topics are featured by many collaborations at the national scale within different networks, e.g. the ’GDR-supersymmetry’ working group and current successors (« Terascale » GDR), or the PNHE. Other external collaborations are also presently going on with researchers from the ATLAS collaboration (CERN, LAL Orsay, CPPM-Marseille, etc), and theorists from CPT-Marseille, mostly through the OCEVU network.

**Cosmology :**

Inflationary models, study of the universe expansion and growth of perturbations ; physics of the very early universe : generation of gravitational waves, evolution of the universe immediately after inflation ; Big Bang Nucleosynthesis (BBN) and the cosmic Lithium 7 problem ; primordial magnetic fields ; semi-analytic methods for fluid mechanics and magneto-hydrodynamics applied to the evolution of astrophysical and cosmological fluids ; modified gravity models (e.g. scalar-tensor, f(R)).

**Non-perturbative QCD :**

study of some nonperturbative Quantum Chromodynamics (QCD) phenomena related to the dynamical properties of hadrons (spectra and decays) using, in particular, the QCD spectral sum rule approach. This method is among the very few analytical ones which uses the fundamental QCD parameters (alpha_s, quark masses, quark and gluon condensates, etc.) and is a robust alternative and/or complement to lattice numerical calculations.

**Quantum field theory : **

Formal aspects in quantum field theory (QFT). Non-perturbative approaches (variationally optimized perturbation, resummations, renormalization group) in field theories and condensed matter : applications in QCD and low energy hadron physics. Studies of phase transitions at finite temperature and density.