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Theory group Michael Joyce *

Theory group Michael Joyce *. Plan. Le groupe et ses collaborations Cadre général de recherche Quelques resultats récents Perspectives. Member s and collaboration s. 1 permanent (MJ) + doctorants (quatre depuis 2007)

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Theory group Michael Joyce *

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  1. Theory group Michael Joyce *

  2. Plan • Le groupe et ses collaborations • Cadre général de recherche • Quelques resultats récents • Perspectives

  3. Members and collaborations 1 permanent (MJ) + doctorants (quatre depuis 2007) + External french collaborations: LPTMC(UPMC), Université de Nice + External non-french collaborations: Rome, Copenhagen (NBI)

  4. Overview of research

  5. Principal Motivation: The problem of structure formation ??  WMAP : the universe aged ~105 years… SDSS : the universe today (1010 years) Density fluctuations ~10-5 Fluctuations >> 1 How do these structures come from these initial conditions ? Theory furnishes predictions also for other observations (weak lensing, dark matter searches…)

  6. Overview Cosmological structure formation Linear Regime: simple and resolved analytically Non-linear regime: intractable, essentially numerical resolution

  7. Structure formation in the standard cosmological model: millenium Millenium simulations:

  8. Overview Cosmological simulations: limitations Numerical simulations • (still) have limited spatial resolution • use approximate (N-body) methods, precision is not established • They lead to purely phenomenological descriptions (e.g halo models) • Even if « dissipationless» (i.e. gravity only) poor understanding of physics

  9. Overview Goals of research To improve understanding of physics of non-linear regime of clustering • [ To improve accuracy of our description of non-linear clustering for comparison with observations ] • Recent years: • Mostly purely self-gravitating systems • Broad framework  statistical mechanics of long-range systems

  10. Thèses récentes • FrançoisSICARD • Out of equilibrium dynamics of infinite one dimensional self-gravitating systemssoutenue décembre 2010 • Tirawut WORRAKITPOONPON • Relaxation of isolated self-gravitating systems in one and three dimensions, soutenue juin 2011 • David BENHAIEM • Self-similarity and stable clustering in scale-free cosmological models in one and three dimensions soutenue décembre 2013 • Jules MORAND • Dynamics of long-range interacting systems beyond the Vlasov limit soutenue décembre 2014

  11. Some recent publications D. Benhaiem and M. Joyce, Self-similarity and stable clustering in a family of scale-free cosmologies Mon. Not. R. Astron. Soc. 394, 791 (2014) I. Carucci, M. Sparre, S. Hansen and M.Joyce Particle ejection during mergers of dark matter halos JCAP 06, 57 (2014) -------------------------- M. Joyce, P. Viot and J. Morand Scaling Quasistationary States in Long-Range Systems with Dissipation Phys. Rev. Lett., 112, 070602(2014) A. Gabrielli, M. Joyce and J. Morand, Finite-N corrections to Vlasov dynamics and the range of pair interactions, Phys. Rev. E90, 062910 (2014)

  12. Some recent results

  13. Non-linear clustering in scale-free cosmologies David Benhaiem, MJ and Bruno Marcos Mon. Not. R. Astron. Soc. (2014) Equations of motion of N-body simulations (in general): Can be recast in new “time” variable as where i.e. self gravitating particles subjected to a fluid damping

  14. Effective damping in standard cosmology

  15. scale-free cosmologies • If • Initial power spectrum P(k) ~ kn • « Damping coefficient » kappa independent of time • the model is « scale-free » • Only one relevant characteristic scale •  clustering must be « self-similar » • temporal evolution = trivial rescaling of coordinates • Provides very powerful control on numerical simulation

  16. Effect of expansion rate on structure formation small damping large damping

  17. Scale-free models: dependence of NL clustering on cosmology

  18. Scale-free models: resolution and stable clustering

  19. self-similarity tests: some conclusions • Resolution improves in time in a strongly model-dependent way • The analytical prediction of stable clustering provides a very good approximation to the well resolved non-linear regime • Currently in preparation: • Halo profiles in this family of cosmologies…universality of halos (NFW)? • Conclusions: • universality broken in large part of model space • slope of outer part of profile is clearly model dependent

  20. Application to dark energy models? A very large family of dark energy models can be approximated as interpolations through our scale-free family:  Construction of semi-analytical approximations for clustering statistics

  21. Perspectives

  22. Perspectives • Short-term focus on consolidating and developing external collaborations (no thesis student recruted this year). Sabbatical MJ next year? • Medium-long term: focus more on cosmological orientation or statistical mechanics ? • Stat mech: possibility of collaboration with experimental group at NTU Singapore • Recrutement of post-doc (Comité théorie in2p3?) with numerical orientation would greatly boost cosmological aspects

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