Articles
Large Scale Structures
Relativistic cosmological large scale structures at one-loopHere, we calculate the one-loop bispectrum including leading relativistic corrections due to the dynamics of the perturbations. Naively, it is expected that the relativistic corrections are negligible both on large scales because the universe is in the linear regime and on small scales because Newtonian equations holds. However, the bispectrum couples scales and in the squeezed limit, we find that the 1-loop relativistic corrections are of the same order of magnitude than the Newtonian results. It is also of the same order of magnitude than the signal that would be induced by primordial non-Gaussianities of the local type. Some codes that we used are given "as if" to the community here.
Quantum field theory in curved spacetime: Schwinger effect in de Sitter
Semiclassical estimate of fermionic pair creation in 3+1D de Sitter spacetime:We generalized in this work flat spacetime techniques to computed the number of fermionic pair produced via Schwinger mechanism in de Sitter spacetime. Our results are valid for any one component electrical field configuration and we presented the explicit example of a constant electrical field. In the latter no difference between the bosonic and the fermionic pair creation rate is reported.
C. Stahl, E. Strobel, AIP Conf.Proc. 1693 050005 (2015)
Fermionic current and Schwinger effect in de Sitter spacetime
In this work, we went further in exploring the Schwinger effect in curved spacetimes. To do so we defined the induced current which is a better quantity to describe the Schwinger effect in curved spacetime since it does not require the notion of particle. Then it is possible to find analytic solution to the Dirac equation in de Sitter spacetime for a constant electrical field. After a long calculation which demands complex integration coupled with patience, it was possible to propose a final expression for the induced current which was different from the bosonic one. This is a really interesting step in aiming at understand Schwinger effect in curved spacetime because in the equivalent problem in flat spacetime, both number of boson and fermion produced are equal.
C. Stahl, E. Strobel, S.-S. Xue, Phys. Rev. D 93 025004 (2016)
Pair Creation in the early universe.
This proceeding sums up my research in de Sitter spacetime at the beggining of 2016. I proposed also an interesting possible connection with the multiverse proposal.
Scalar current of created pairs by Schwinger mechanism in de Sitter spacetime
We investigate there the Schwinger scalar pair creation in 1+d dimensional spacetime with a special focus on 1+2 D where we computed the induced current. We report as in 1+3 D and 1+1 D infrared hyperconductivity. We also proposed a connection between tachyons, conformality and infrared hyperconductivity.
E. Bavarsad, C. Stahl, S.-S. Xue, Phys.Rev. D 94 104011 (2016)
Effect of a magnetic field on Schwinger mechanism in de Sitter spacetime
In this article and in its accompanying proceeding (which numerically investigates more cases), we generalize our previsous investigations on Schwinger effect in de Sitter to the case with a constant magnetic field and a constant electric field. The calculation is as involved as before and requires to use zeta-renormalization techniques. Our finding is that unlike flat space time results, the presence of the magnetic field enhances the pair production.
E. Bavarsad, S-P. Kim, C. Stahl, S.-S. Xue, Phys.Rev. D 96 no.2, 025017 (2018)
Backreaction and magnetogenesis
Schwinger effect and backreaction in de Sitter spacetimeIn all my previous works, we described how pairs of particle-antiparticles can be created during inflation under the influence of a strong constant electric field. In this letter, we show our first results about how these pairs backreact to the electric field. We found two interesting results namely the presence of plasma oscillations like in the analog flat spacetime problem and a possible way of amplifying the electromagnetic field during a phase of inflation which could be a new path to the open question of cosmological magnetogenesis that I investigate in the next article.
C. Stahl, S.-S. Xue, Phys.Lett. B 760 (2016) 288-292
Schwinger effect impacting primordial magnetogenesis
In this work, I investigated how the presence of negative conductivity could affect a scenario of magnetogenesis. It is found that the magnetic field gets amplified but its strength is not enough to seed the present observed magnetic field. A negative conductivity is very counter intuitive. I may come from renormalization or from non-linear (in E and B) corrections to the Einstein-Maxwell equations: the Euler-Heisenberg-Einstein lagrangian.
Cosmological black holes
Charged cosmological Black-holesIn this article, we introduced the charge cosmological black hole, discuss various of its properties and propose a astrophysical application of this black hole: to challenge a scenario of production of gamma ray burst: the fireshell model.
Interacting Dark Energy
A model of interacting dark fluids tested with supernovae dataMany models positing a possible interaction between dark energy and dark matter exist. Most of them are following the trendy idea of "data driven science". However, few theoretical roots were proposed for those models. Our model: QFC (Quantum Field Theory) proposes to use an Einstein-Cartan theory of gravity, where our current universe is in a fixed point of the beta-function. The theory predicts the presence of two new parameters, that control the rate of exchange between dark energy and dark matter. We constrained those parameters with supernovae and baryon acoustic oscillations data.
Inhomogeneous universes
Inhomogeneous matter distribution and supernovaeCosmological fractal matter with an upper cutoff
In those articles, one can find a model of inhomogeneous matter distribution that I proposed as an alternative to dark energy. In this framework, dark energy is nothing but a mirage due to a clumpy matter distribution.
C. Stahl, Int. J. Mod. Phys. D 25, 1650066
R.Ruffini and C.Stahl, proceeding of MG14
Loop Quantum Cosmology
Comparison of primordial tensor power spectra from the deformed algebra and dressed metric approaches in loop quantum cosmologyIn this article, based on my work during my master thesis, we computed quantum corrections to the dynamics of the inflaton field and to the tensor power spectrum at the end of the inflation with two different approach to loop quantum cosmology.
B. Bolliet, J. Grain, C. Stahl, L. Linsefors, A. Barrau, Phys. Rev. D 91 084035 (2015).