Tina Kahniashvili

Microwave background signatures of a primordial stochastic magnetic field

A stochastic magnetic field in the early Universe will produce anisotropies in the temperature and polarization of the cosmic microwave background. We derive analytic expressions for the microwave background temperature and polarization power spectra induced by vector and tensor perturbations from a power-law magnetic field. For a scale-invariant stochastic magnetic field smoothed over a comoving scale of

Faraday rotation of the Cosmic Microwave Background polarization by a stochastic magnetic field

1 {\rm Mpc}

Tensor microwave anisotropies from a stochastic magnetic field

, the MAP satellite has the potential to constrain the comoving mean-field amplitude to be no greater than approximately

CMB temperature anisotropy from broken spatial isotropy due to a homogeneous cosmological magnetic field

2\times10^{-9}

Spectrum of gravitational radiation from primordial turbulence

G. Limits improve as the power-law slope increases: for causally-generated power-law magnetic fields, the comoving mean-field amplitude has an upper bound of approximately

Effects of cosmological magnetic helicity on the cosmic microwave background

4\times10^{-13} {\rm G}

Microwave background anisotropies from Alfvén waves

. Such constraints will surpass all current limits on galactic-scale primordial stochastic magnetic fields at decoupling.

Nonhelical Inverse Transfer of a Decaying Turbulent Magnetic Field

A primordial cosmological magnetic field induces Faraday rotation of the cosmic microwave background polarization. This rotation produces a curl-type polarization component even when the unrotated polarization possesses only gradient-type polarization, as expected from scalar density perturbations. We compute the angular power spectrum of curl-type polarization arising from small Faraday rotation due to a weak stochastic primordial magnetic field with a power-law power spectrum. The induced polarization power spectrum peaks at arc minute angular scales. Faraday rotation is one of the few cosmological sources of curl-type polarization, along with primordial tensor perturbations, gravitational lensing, and the vector and tensor perturbations induced by magnetic fields; the Faraday rotation signal peaks on significantly smaller angular scales than any of these, with a power spectrum amplitude which can be comparable to that from gravitational lensing. Prospects for detection are briefly discussed.

Evolution of Primordial Magnetic Fields from Phase Transitions

We derive an expression for the angular power spectrum of cosmic microwave background anisotropies due to gravity waves generated by a stochastic magnetic field and compare the result with current observations; we take into account the non-linear nature of the stress energy tensor of the magnetic field. For almost scale invariant spectra, the amplitude of the magnetic field at galactic scales is constrained to be of order 10-9 G. If we assume that the magnetic field is damped below the Alfven damping scale, we find that its amplitude at 0.1h-1 Mpc, B?, is constrained to be B? -3/2, where n is the spectral index of the magnetic field and H0=100h km s-1 Mpc-1 is the Hubble constant today.

Detectability of gravitational waves from phase transitions

We derive the cosmic microwave background temperature anisotropy two-point correlation function (including off-diagonal correlations) from broken spatial isotropy due to an arbitrarily oriented homogeneous cosmological magnetic field.