Primordial magnetic field limits from cosmological data

We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically-relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.Comment: 7 pages, 6 figure

Evolution of inflation-generated magnetic field through phase transitions

We study the evolution of an inflation-generated magnetic field, due to its coupling to fluid motions, during cosmological phase transitions. We find that the magnetic field stays almost unchanged on large scales, while on small scales, the spectrum is modified in such a way that power at small scales becomes progressively suppressed. We also show that the magnetic field generates turbulent motions in the initially turbulence-free plasma. On large scales, the slope of the resulting kinetic energy spectrum is consistent with that of white noise

Numerical simulations of the decay of primordial magnetic turbulence

We perform direct numerical simulations of forced and freely decaying 3D magnetohydrodynamic turbulence in order to model magnetic field evolution during cosmological phase transitions in the early Universe. Our approach assumes the existence of a magnetic field generated either by a process during inflation or shortly thereafter, or by bubble collisions during a phase transition. We show that the final configuration of the magnetic field depends on the initial conditions, while the velocity field is nearly independent of initial conditions.Comment: 10 pages, 6 figures, references added, PRD accepte

Constraining primordial magnetic fields through large scale structure

We study primordial magnetic field effects on the matter perturbations in the universe. We assume magnetic field generation prior to the big bang nucleosynthesis (BBN), i.e., during the radiation-dominated epoch of the universe expansion, but do not limit analysis by considering a particular magnetogenesis scenario. Contrary to previous studies, we limit the total magnetic field energy density and not the smoothed amplitude of the magnetic field at large (of the order of 1 Mpc) scales. We review several cosmological signatures, such as halo abundance, thermal Sunyaev-Zel'dovich (tSZ) effect, and Lyman-α data. For a cross-check we compare our limits with that obtained through the CMB faraday rotation effect and BBN. The limits range between 1.5 nG and 4.5 nG for n[subscript B]∈ in (– 3; –1.5)

Evolution of Primordial Magnetic Fields from Phase Transitions

We consider the evolution of primordial magnetic fields generated during cosmological, electroweak or QCD, phase transitions. We assume that the magnetic field generation can be described as an injection of magnetic energy to cosmological plasma at a given scale determined by the moment of magnetic field generation. A high Reynolds number ensures strong coupling between magnetic field and fluid motions. The subsequent evolution of the magnetic field is governed by decaying hydromagnetic turbulence. Both our numerical simulations and a phenomenological description allow us to recover "universal" laws for the decay of magnetic energy and the growth of magnetic correlation length in the turbulent (low viscosity) regime. In particular, we show that during the radiation dominated epoch, energy and correlation length of non-helical magnetic fields scale as conformal time to the powers −1/2 and +1/2, respectively. For helical magnetic fields, energy and correlation length scale as conformal time to the powers −1/3 and +2/3, respectively. The universal decay law of the magnetic field implies that the strength of magnetic field generated during the QCD phase transition could reach ∼ 10 −9 G with the present day correlation length ∼ 50 kpc. The fields generated at the electroweak phase transition could be as strong as ∼ 10 −10 G with correlation lengths reaching ∼ 0.3 kpc. These values of the magnetic fields are consistent with the lower bounds of the extragalactic magnetic fields

Aerodynamic sound generation by turbulence in shear flows

The nonlinear aerodynamic sound generation by turbulence has been long analyzed since the foundation of the theory of aerodynamic sound in pioneering paper by Lighthill 1. Also, it was Lighthill 2 who noted that velocity shear can increase the acoustic wave emission in the aerodynamic situation due to the existence of linear terms in the inhomogeneous part of the analogy equations (second derivative of the Reynolds stress). In 3 it was disclosed and described a linear aerodynamic sound generation mechanism. Specifically, it was shown that the flow non-normality induced linear phenomenon of the conversion of vortex mode into the acoustic wave mode is the only contributor to the acoustic wave production of the unbounded shear flows in the linear regime. From the physical point of view the potential vorticity was identified as the linear source of acoustic waves in shear flows