arXiv subjects

Kerstin E. Kunze

Publications and source records attributed to Kerstin E. Kunze.

At least 19 recordsLinked to original sources

arXiv2026

Effects of primordial magnetic fields on 21 cm multifrequency angular power spectra

The redshifted cosmic 21 cm line signal of neutral hydrogen provides the possibility to constrain the matter power spectrum. Cross correlating temperature maps at different frequencies (corresponding to different redshifts along the line of sight) allows to determine multifrequency angular power spectra. Primordial magnetic fields raise the amplitude of the linear matter power spectrum on small scales dominating over the contribution of the adiabatic primordial curvature mode. Multifrequency angular power spectra could provide a new possibility to probe primordial magnetic fields including its evolution present before decoupling. Here first multifrequency angular power spectra of the 21 cm line signal are obtained for cosmological models including the adiabatic, primordial curvature mode as well as the compensated magnetic mode for different values of the magnetic field parameters. For this temperature maps are simulated with the modified linear matter power spectra for magnetic fields with magnetic field strength $B_0=4$ nG and spectral indices $n_B=-2.9$ and $n_B=-2.5$, respectively, which have been chosen as examples. Moreover foregrounds have not been taken into account. As examples these multifrequency angular power spectra have been calculated for frequency ranges set around central frequencies of uGMRT Band 3 data as well as MeerKAT L band data. For these using only system noise signal-over-noise ratios are obtained as well as for SKA1-MID which is part of the currently under construction SKAO. Within this simple model results of this first study seem to be promising for constraining magnetic field parameters especially for SKA1-MID.

astro-ph.CO↗

arXiv2023

Cross correlations of the CMB Doppler mode and the 21 cm brightness temperature in the presence of a primordial magnetic field

The cross correlation between the CMB Doppler mode and the 21 cm line brightness temperature is calculated in the presence of a stochastic primordial magnetic field. Potential detectability is estimated for Planck 2018 bestfit parameters in combination with configuration and survey design parameters of 21 cm line radio telescopes such as LOFAR and the future SKAO. Homogeneous as well as inhomogeneous reionization has been considered. In particular the latter in combination with SKA1-mid shows promising signal-over-noise ratios.

astro-ph.CO↗

arXiv2022

Penrose limits of inhomogeneous space-times, their diagonalizability and twistors

Penrose limits are considered in space-times admitting two abelian, space-like Killing vectors in vacuum as well as in the presence of an electromagnetic field. This type of space-times describe inhomogeneous cosmologies as well as colliding plane gravitational and electromagnetic waves. Following the work of Tod [1] the conditions for diagonal Penrose limits are investigated in these backgrounds. The twistor equation is considered in these space-times and solutions given in the Penrose limit.

gr-qc↗

arXiv2022

Magnetic field back reaction on the matter power spectrum

At lowest order comoving magnetic fields which are frozen-into the expanding cosmic fluid do not evolve in time. At next-to-leading order the induction equation is sourced by the interaction term between the baryon velocity and the magnetic field amplitude which leads to a non-trivial evolution of the comoving magnetic field. Moreover, it induces non-trivial cross correlations between the adiabatic curvature mode and the magnetic mode. This cross correlation together with the evolution of the induced matter perturbation leads to interesting effects on the total matter power spectrum at small scales.

astro-ph.CO↗

arXiv2021

CMB anisotropies and linear matter power spectrum in models with non-thermal neutrinos and primordial magnetic fields

Angular power spectra of temperature anisotropies and polarization of the cosmic microwave background (CMB) as well as the linear matter power spectra are calculated for models with three light neutrinos with non-thermal phase-space distributions in the presence of a primordial stochastic magnetic field. The non-thermal phase-space distribution function is assumed to be the sum of a Fermi-Dirac and a gaussian distribution. It is found that the known effective description of the non-thermal model in terms of a twin thermal model with extra relativistic degrees of freedom can also be extended to models including a stochastic magnetic field. Numerical solutions are obtained for a range of magnetic field parameters.

astro-ph.CO↗

arXiv2020

Constraining the primordial magnetic field with dwarf galaxy simulations

Using a set of cosmological hydro-dynamical simulations, we constrained the properties of primordial magnetic fields by studying their impact on the formation and evolution of dwarf galaxies. We performed a large set of simulations (8 dark matter only and 72 chemo-hydrodynamical) including primordial magnetic fields through the extra density fluctuations they induce at small length scales ($k \geq 10\,h\,\rm{Mpc^{-1}}$) in the matter power spectrum. We explored a large variety of primordial magnetic fields with strength $B_λ$ ranging from $0.05$ to $0.50\,\textrm{nG}$ and magnetic energy spectrum slopes $n_B$ from $-2.9$ to $-2.1$. Strong magnetic fields characterized by a high amplitude ($B_λ=0.50,\,0.20\,\textrm{nG}$ with $n_B=-2.9$) or by a steep initial power spectrum slope ($n_B=-2.1,-2.4$, with $B_λ=0.05\,\textrm{nG}$) induce perturbations in the mass scales from $10^7$ to $10^9\,\rm{M}_{\odot}$. In this context emerging galaxies see their star formation rate strongly boosted. They become more luminous and metal rich than their counterparts without primordial magnetic fields. Such strong fields are ruled out by their inability to reproduce the observed scaling relations of dwarf galaxies. They predict dwarf galaxies to be at the origin of an unrealistically early reionization of the Universe and also overproduce luminous satellites in the Local Group. Weaker magnetic fields impacting the primordial density field at corresponding masses $\lesssim 10^6\,\rm{M}_{\odot}$, produce a large number of mini dark halos orbiting the dwarfs, however out of reach for current lensing observations. This study allows for the first time to constrain the properties of primordial magnetic fields based on realistic cosmological simulations of dwarf galaxies.

astro-ph.GA↗

arXiv2020

The Case for Probe-class NASA Astrophysics Missions

Astrophysics spans an enormous range of questions on scales from individual planets to the entire cosmos. To address the richness of 21st century astrophysics requires a corresponding richness of telescopes spanning all bands and all messengers. Much scientific benefit comes from having the multi-wavelength capability available at the same time. Most of these bands,or measurement sensitivities, require space-based missions. Historically, NASA has addressed this need for breadth with a small number of flagship-class missions and a larger number of Explorer missions. While the Explorer program continues to flourish, there is a large gap between Explorers and strategic missions. A fortunate combination of new astrophysics technologies with new, high capacity, low dollar-per-kg to orbit launchers, and new satellite buses allow for cheaper missions with capabilities approaching strategic mission levels. NASA has recognized these developments by calling for Probe-class mission ideas for mission studies, spanning most of the electromagnetic spectrum from GeV gamma-rays to the far infrared, and the new messengers of neutrinos and ultra-high energy cosmic rays. The key insight from the Probes exercise is that order-of-magnitude advances in science performance metrics are possible across the board for initial total cost estimates in the range 500M-1B dollars.

astro-ph.IM↗

arXiv2018

21 cm line signal from magnetic modes

The Lorentz term raises the linear matter power on small scale which leads to interesting signatures in the 21 cm signal. Numerical simulations of the resuting nonlinear density field, the distribution of ionized hydrogen and the 21 cm signal at different values of redshift are presented for magnetic fields with field strength B=5 nG, and spectral indices $n_B=-2.9, -2.2$ and -1.5 together with the adiabatic mode for the best fit data of Planck13+WP. Comparing the averaged global 21 cm signal with the projected SKA1-LOW sensitivities of the Square Kilometre Array (SKA) it might be possible to constrain the magnetic field parameters.

astro-ph.CO↗

arXiv2017

Effects on the CMB from magnetic field dissipation before recombination

Magnetic fields present before decoupling are damped due to radiative viscosity. This energy injection affects the thermal and ionization history of the cosmic plasma. The implications for the CMB anisotropies and polarization are investigated for different parameter choices of a non helical stochastic magnetic field. Assuming a Gaussian smoothing scale determined by the magnetic damping wave number at recombination it is found that magnetic fields with present day strength less than 0.1 nG and negative magnetic spectral indices have a sizeable effect on the CMB temperature anisotropies and polarization.

astro-ph.CO↗

arXiv2016

An introduction to cosmology

Cosmology is becoming an important tool to test particle physics models. We provide an overview of the standard model of cosmology with an emphasis on the observations relevant for testing fundamental physics.

astro-ph.CO↗

arXiv2015

Constraints on hidden photons from current and future observations of CMB spectral distortions

A variety of beyond the standard model scenarios contain very light hidden sector U(1) gauge bosons undergoing kinetic mixing with the photon. The resulting oscillation between ordinary and hidden photons leads to spectral distortions of the cosmic microwave background. We update the bounds on the mixing parameter $χ_0$ and the mass of the hidden photon $m_{γ'}$ for future experiments measuring CMB spectral distortions, such as PIXIE and PRISM/COrE. For $10^{-14}\;{\rm eV}\lesssim m_{γ'}\lesssim 10^{-13}\;{\rm eV}$, we find the kinetic mixing angle $χ_0$ has to be less than $10^{-8}$ at 95\% CL. These bounds are more than an order of magnitude stronger than those derived from the COBE/FIRAS data.

astro-ph.CO↗

arXiv2015

Constraints on primordial magnetic fields from the optical depth of the cosmic microwave background

Damping of magnetic fields via ambipolar diffusion and decay of magnetohydrodynamical (MHD) turbulence in the post decoupling era heats the intergalactic medium (IGM). Delayed recombination of hydrogen atoms in the IGM yields an optical depth to scattering of the cosmic microwave background (CMB). The optical depth generated at $z\gg 10$ does not affect the "reionization bump" of the CMB polarization power spectrum at low multipoles, but affects the temperature and polarization power spectra at high multipoles. Writing the present-day energy density of fields smoothed over the damping scale at the decoupling epoch as $ρ_{B,0}=B_{0}^2/2$, we constrain $B_0$ as a function of the spectral index, $n_B$. Using the Planck 2013 likelihood code that uses the Planck temperature and lensing data together with the WMAP 9-year polarization data, we find the 95% upper bounds of $B_0<0.63$, 0.39, and 0.18~nG for $n_B=-2.9$, $-2.5$, and $-1.5$, respectively. For these spectral indices, the optical depth is dominated by dissipation of the decaying MHD turbulence that occurs shortly after the decoupling epoch. Our limits are stronger than the previous limits ignoring the effects of the fields on ionization history. Inverse Compton scattering of CMB photons off electrons in the heated IGM distorts the thermal spectrum of CMB. Our limits on $B_0$ imply that the $y$-type distortion from dissipation of fields in the post decoupling era should be smaller than $10^{-9}$, $4\times10^{-9}$, and $10^{-9}$, respectively.

astro-ph.CO↗

arXiv2014

Generic inference of inflation models by local non-Gaussianity

The presence of multiple fields during inflation might seed a detectable amount of non-Gaussianity in the curvature perturbations, which in turn becomes observable in present data sets like the cosmic microwave background (CMB) or the large scale structure (LSS). Within this proceeding we present a fully analytic method to infer inflationary parameters from observations by exploiting higher-order statistics of the curvature perturbations. To keep this analyticity, and thereby to dispense with numerically expensive sampling techniques, a saddle-point approximation is introduced whose precision has been validated for a numerical toy example. Applied to real data, this approach might enable to discriminate among the still viable models of inflation.

astro-ph.CO↗

arXiv2014

Generic inference of inflation models by non-Gaussianity and primordial power spectrum reconstruction

We present a generic inference method for inflation models from observational data by the usage of higher-order statistics of the curvature perturbation on uniform density hypersurfaces. This method is based on the calculation of the posterior for the primordial non-Gaussianity parameters $f_\text{NL}$ and $g_\text{NL}$, which in general depend on specific parameters of inflation and reheating models, and enables to discriminate among the still viable inflation models. To keep analyticity as far as possible to dispense with numerically expensive sampling techniques a saddle-point approximation is introduced, whose precision is validated for a numerical toy example. The mathematical formulation is done in a generic way so that the approach remains applicable to cosmic microwave background data as well as to large scale structure data. Additionally, we review a few currently interesting inflation models and present numerical toy examples thereof in two and three dimensions to demonstrate the efficiency of the higher-order statistics method. A second quantity of interest is the primordial power spectrum. Here, we present two Bayesian methods to infer it from observational data, the so called critical filter and an extension thereof with smoothness prior, both allowing for a non-parametric spectrum reconstruction. These methods are able to reconstruct the spectra of the observed perturbations and the primordial ones of curvature perturbation even in case of non-Gaussianity and partial sky coverage. We argue that observables like $T-$ and $B-$modes permit to measure both spectra. This also allows to infer the level of non-Gaussianity generated since inflation.

astro-ph.CO↗

arXiv2014

Secondary CMB anisotropies from bulk motions in the presence of stochastic magnetic fields

Bulk motions of electrons along the line of sight induce secondary temperature fluctuations in the post-decoupling, reionized universe. In the presence of a magnetic field not only the scalar mode but also the vector mode act as a source for the bulk motion. The resulting angular power spectrum of temperature anisotropies of the cosmic microwave background is calculated assuming a simple model of reionization.Contributions from the standard adiabatic, curvature mode and a non helical magnetic field are included. The contribution due to magnetic fields with field strengths of order nG and negative magnetic spectral indices becomes important for multipoles larger than $\ell \sim 10^4$.

astro-ph.CO↗

arXiv2013

Constraining primordial magnetic fields with distortions of the black-body spectrum of the cosmic microwave background: pre- and post-decoupling contributions

Observational limits on $y$- and $μ$-type distortions can constrain properties of magnetic fields in the early universe. For a Gaussian, random, and non-helical field, $μ$ and $y$ are calculated a function of the present-day strength of the field, $B_0$, smoothed over a certain Gaussian width, $k_c^{-1}$, and spectral index, $n_B$, defined by $P_B(k)\propto k^{n_B}$. For $n_B=-2.9$ and $k_c^{-1}=1 {\rm Mpc}$, the COBE/FIRAS limit on $μ$ yields $B_0<40$ nG, whereas the projected PIXIE limit on $μ$ would yield $B_0<0.8$ nG. For non-scale-invariant spectra, constraints can be stronger. For $B_0=1$ nG with $k_c^{-1}=1 {\rm Mpc}$, the COBE/FIRAS limit on $μ$ excludes a wide range of spectral indices given by $n_B>-2.6$. After decoupling, energy dissipation is due to ambipolar diffusion and decaying MHD turbulence, creating a $y$-type distortion. The distortion is completely dominated by decaying MHD turbulence, and is of order $y\approx 10^{-7}$ for a few nG field smoothed over the damping scale at the decoupling epoch, $k_{d,dec}\approx 290 (B_0/1 {\rm nG})^{-1} {\rm Mpc}^{-1}$. This contribution is as large as those of the known contributions such as reionization and virialized objects at lower redshifts. The projected PIXIE limit on $y$ would exclude $B_0>1.0$ and 0.6 nG for $n_B=-2.9$ and -2.3, respectively, and $B_0>0.6$ nG for $n_B\geq 2$. The current limits on the optical depth to Thomson scattering restrict the predicted $y$-type distortion to be $y\lesssim 10^{-8}$. (Abridged)

astro-ph.CO↗

arXiv2013

Cosmological Magnetic Fields

Magnetic fields are observed on nearly all scales in the universe, from stars and galaxies upto galaxy clusters and even beyond. The origin of cosmic magnetic fields is still an open question, however a large class of models puts its origin in the very early universe. A magnetic dynamo amplifying an initial seed magnetic field could explain the present day strength of the galactic magnetic field. However, it is still an open problem how and when this initial magnetic field was created. Observations of the cosmic microwave background (CMB) provide a window to the early universe and might therefore be able to tell us whether cosmic magnetic fields are of primordial, cosmological origin and at the same time constrain its parameters. We will give an overview of the observational evidence of large scale magnetic fields, describe generation mechanisms of primordial magnetic fields and possible imprints in the CMB.

astro-ph.CO↗

arXiv2013

CMB and matter power spectra from cross correlations of primordial curvature and magnetic fields

A complete numerical calculation of the temperature anisotropies and the polarization of the cosmic microwave background (CMB) is presented for a non zero cross correlation of a stochastic magnetic field with the primordial curvature perturbation. Such a cross correlation results, for example, if the magnetic field is generated during inflation by coupling electrodynamics to a scalar field which is identified with the curvaton. For a nearly scale invariant magnetic field of 1 nG it is found that at low multipoles the contribution due to the cross correlation dominates over that of the pure magnetic mode. A similar behaviour on large scales is found for the linear matter power spectrum.

astro-ph.CO↗