Presence Of Primordial Magnetic Field Research Articles

First Star Formation in the Presence of Primordial Magnetic Fields

Abstract It has been recently claimed that primordial magnetic fields could relieve the cosmological Hubble tension. Fields of sufficient strength to relieve this tension would result in a magnetic field whose Alfvén velocity, v a , is comparable to the speed of sound, c s , at the start of structure formation. We consider the impact of such fields on the formation of the first cosmological objects, minihalos (<106 M ⊙), forming stars with zoom-in cosmological simulations tracking a single such minihalo. We seed each simulation with present-day field strengths of 2 × 10−12–2 × 10−10 G corresponding to initial ratios of Alfvén velocity to the speed of sound of v a /c s ≈ 0.03−3. We find that when v a /c s ≪1, the effects are modest. However, when v a ∼ c s , the starting time of the gravitational collapse is delayed and the duration extended as much as by Δz = 2.5 in redshift. When v a > c s , the collapse is completely suppressed and the minihalos continue to grow and are unlikely to collapse until reaching the atomic cooling limit. Employing current observational limits on primordial magnetic fields we conclude that inflationary-produced primordial magnetic fields could have a significant impact on first star formation.

Evolution of axions in the presence of primordial magnetic fields

We study the evolution of axions interacting with primordial magnetic fields (PMFs) starting just from the QCD phase transition in the expanding universe. This interaction is owing to the Primakoff effect. Adopting the zero mode approximation for axions, we derive the system of equations for axions and magnetic fields, where the expansion of the universe and the spectra of magnetic fields are accounted for exactly. We find that the contribution of the Primakoff effect to the dynamics of axions and magnetic fields is rather weak. It confirms some previous estimates leading to analogous conclusions, when accounting here for the Hubble expansion both for an uniform axion field and non-uniform PMFs using Fourier spectra for their energy and helicity densities. We solve the corresponding system of the evolution equations and find that the axion zero mode, when evolving during radiation era, has its amplitude at the level sufficient for that axion to be a good candidate for the cold dark matter.

Corrections to halo model due to primordial magnetic field in a universe with non-zero cosmological constant

We study the corrections to the halo model of structure formation which is traditionally described by the Press Schecter formalism due to the presence of a primordial magnetic field in a universe which has a non-zero cosmological constant $\varLambda $ and positive curvature $k=+1$. We have used the result of Lokas and Hoffman (Astrophys. J. Lett. 542:139, 2000) and our earlier work (Nigam and Varalakshmi in Astrophys. Space Sci. 362:10, 2017) to incorporate the influence of both B field and $\varLambda $. We tune the value of the primordial magnetic field strength from 0.1 nG to 10 nG while varying the parameter $\lambda $ which is defined in terms of the cosmological constant $\varLambda $ and the Hubble constant $H_{o}$ from 0.5 to 0.75. We study the change in the Press Schecter number distribution of the dark matter halos as a function of these parameters. We find that while in general the presence of $\lambda $ disrupts the halo formation in presence of background primordial magnetic field, but as the value of $\lambda $ is increased above 0.65, there is a sudden fall in the halo count. Further we find that the model is far more sensitive to the variation in $\lambda $ than to the primordial magnetic field. This essentially means that the halo count has a strong correlation with $\lambda $ for fixed field strength than with the field strength for a fixed $\lambda $.

An Upper Limit on Primordial Magnetic Fields from Ultra-faint Dwarf Galaxies

Abstract The presence of primordial magnetic fields increases the minimum halo mass in which star formation is possible at high redshifts. Estimates of the dynamical mass of ultra-faint dwarf galaxies (UFDs) within their half-light radius constrain their virialized halo mass before their infall into the Milky Way. The inferred halo mass and formation redshift of the UFDs place upper bounds on the primordial comoving magnetic field, B 0. We derive an upper limit of 0.50 ± 0.086 (0.31 ± 0.04) nG on B 0 assuming the average formation redshift of the UFD host halos is z form = 10 (20), respectively.

Corrections to halo model in presence of primordial magnetic field

We study the role played by the primordial magnetic field in the process of structure formation in the early universe. We have compared the halo mass abundance in the presence and absence of the magnetic field. We derive a modified Press-Schechter formula in presence of another source for matter perturbation and use it to study how this extra source affects halo count. This other source is the magnetic field with a given power spectrum. We find the ranges for the magnetic field strength over which the field enhances the halo formation for a mass range for spectral index \(n_{b} = -2.95\). We found that for field strength less than or equal to \(B = 7.0~\mbox{nG}\), which we call the cut-off field strength, the presence of magnetic field enhances halo formation at low mass scale while it disrupts for a stronger field. We further investigate the dependence of halo count on the spectral index of the magnetic field power spectrum. We observe that at the cut-off field strength, halo formation is disrupted for a spectral index larger than −2.9. We carry out similar investigation for the more generic ellipsoidal collapse where the mass function is given by the Sheth-Tormen formula. For this case we find the cut-off field strength is \(5.5~\mbox{nG}\).

Cosmological constraints on axionic dark radiation from axion-photon conversion in the early Universe

Axions seem ubiquitous in string theories and some of them may be produced non-thermally by heavy scalar decays, contributing to dark radiation. We study various cosmological effects of photons produced from the axionic dark radiation through axion-photon conversion in the presence of primordial magnetic fields, and derive tight constraints on the combination of the axion-photon coupling and the primordialmagnetic field.

PROBING PRIMORDIAL MAGNETIC FIELDS USING Lyα CLOUDS

From previous studies of the effect of primordial magnetic fields on early structure formation, we know that the presence of primordial magnetic fields during early structure formation could induce more perturbations at small scales (at present 1-10 Mpc/h) as compared to the usual LCDM theory. Matter power spectrum over these scales are effectively probed by cosmological observables such as shear correlation and Ly-alpha clouds, In this paper we discuss the implications of primordial magnetic fields on the distribution of Ly-alpha clouds. We simulate the line of sight density fluctuation including the contribution coming from the primordial magnetic fields. We compute the evolution of Ly-alpha opacity for this case and compare our theoretical estimates of Ly-alpha opacity with the existing data to constrain the parameters of the primordial magnetic fields. We also discuss the case when the two density fields are correlated. Our analysis yields an upper bounds of roughly 0.3-0.6 nG on the magnetic field strength for a range of nearly scale invariant models, corresponding to magnetic field power spectrum index n \simeq -3.

Bipolar harmonic encoding of CMB correlation patterns

Deviations from statistical isotropy can be modeled in various ways, for instance, anisotropic cosmological models (Bianchi models), compact topologies, and presence of primordial magnetic field. Signature of anisotropy manifests itself in cosmic microwave background correlation patterns. Here we explore the symmetries of the correlation function and its implications on the observable measures constructed within the bipolar harmonic formalism for these variety of models. Different quantifiers within the bipolar harmonic representation are used to distinguish between plausible models of breakdown of statistical isotropy and as a spectroscopic tool for discriminating between distinct cosmic topology.

NEUTRINO MASS AND COLD DARK MATTER PARTICLES IN BIG-BANG NUCLEOSYNTHESIS

Neutrino is a tiny weakly interacting massive particle, but it has strong impacts on various cosmological and astrophysical phenomena. Neutrinos play a critical role in nucleosynthesis of light-to-heavy mass elements in core-collapse supernovae. The light element synthesis is particularly affected by neutrino oscillation (MSW) effect through the ν-process. We propose first that precise determination of sin 2 2θ13 and mass hierarchy can be made by a theoretical study of the observed 7 Li /11 B ratio in stars and presolar grains which are produced from SN ejecta. Theoretical sensitivity in our proposed method is shown to be superior to ongoing long-baseline neutrino experiments for the parameter region 10−4 ≤ sin22θ13 ≤ 10−2. We secondly discuss how to constrain the neutrino mass Σmν from precise analysis of cosmic microwave background anisotropies in the presence of primordial magnetic field. We obtain an upper limit Σmν < 1.3 eV (2σ). Thirdly, we discuss decaying dark-matter particle model in order to solve the primordial lithium problems that the standard Big-Bang nucleosynthesis theory predicts extremely different 6 Li and 7 Li abundances from observations.

Microwave background anisotropies from Alfvén waves

We investigate microwave background anisotropies in the presence of primordial magnetic fields. We show that a homogeneous field with fixed direction can amplify vector perturbations. We calculate the correlations of δT/T explicitly and show that a large scale coherent field induces correlations between al-1,m and al+1,m. We discuss constraints on the amplitude and spectrum of a primordial magnetic field imposed by observations of CMB anisotropies.

The paradox of axions surviving primordial magnetic fiels

In the presence of primordial magnetic fields the oscillating cosmic axion field drives an oscillating electric field. The ensuing dissipation of axions is found to be inversely proportional to the conductivity of the primordial plasma. This counterintuitive result is essentially equivalent to “Zeno's paradox” or the “watched-pot effect” of quantum mechanics. It implies that the standard predictions of the cosmic axion density remain unaltered even if primordial magnetic fields are strong.