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Register a new userMagnetic fields from cosmological bulk flows
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Added by
Hector Villarrubia-Rojo
Publication date
2019
fields
Physics
and research's language is
English
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We explore the possibility that matter bulk flows could generate the required vorticity in the electron-proton-photon plasma to source cosmic magnetic fields through the Harrison mechanism. We analyze the coupled set of perturbed Maxwell and Boltzmann equations for a plasma in which the matter and radiation components exhibit relative bulk motions at the background level. We find that, to first order in cosmological perturbations, bulk flows with velocities compatible with current Planck limits ($beta<8.5times 10^{-4}$ at $95%$ CL) could generate magnetic fields with an amplitude $10^{-21}$ G on 10 kpc comoving scales at the time of completed galaxy formation which could be sufficient to seed a galactic dynamo mechanism.
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We propose and apply a new test of Einsteins Equivalence Principle (EEP) based on the gravitational redshift induced by the central super massive black hole of quasars in the surrounding accretion disk. Specifically, we compare the observed gravitational redshift of the Fe III$lambdalambda$2039-2113 emission line blend in quasars with the predicted values in a wide, uncharted, cosmic territory ($0 lesssim z_{cosm}lesssim3$). For the first time we measure, with statistical uncertainties comparable or better than those of other classical methods outside the Solar System, the ratio between the observed gravitational redshifts and the theoretical predictions in 10 independent cosmological redshift bins in the $1 lesssim z_{cosm}lesssim3$ range. The average of the measured over predicted gravitational redshifts ratio in this cosmological redshift interval is $langle z^m_g/z_g^prangle=1.05pm 0.06$ with scatter $0.13pm 0.05$ showing no cosmological evolution of EEP within these limits. This method can benefit from larger samples of measurements with better S/N ratios, paving the way for high precision tests (below 1%) of EEP on cosmological scales.
We present validation tests of emulator-based halo model method for cosmological parameter inference, assuming hypothetical measurements of the projected correlation function of galaxies, $w_{rm p}(R)$, and the galaxy-galaxy weak lensing, $Delta!Sigma(R)$, from the spectroscopic SDSS galaxies and the Hyper Suprime-Cam Year1 (HSC-Y1) galaxies. To do this, we use textsc{Dark Emulator} developed in Nishimichi et al. based on an ensemble of $N$-body simulations, which is an emulation package enabling a fast, accurate computation of halo clustering quantities for flat-geometry $w$CDM cosmologies. Adopting the halo occupation distribution, the emulator allows us to obtain model predictions of $Delta!Sigma$ and $w_{rm p}$ for the SDSS-like galaxies at a few CPU seconds for an input set of parameters. We present performance and validation of the method by carrying out Markov Chain Monte Carlo analyses of the mock signals measured from a variety of mock catalogs that mimic the SDSS and HSC-Y1 galaxies. We show that the halo model method can recover the underlying true cosmological parameters to within the 68% credible interval, except for the mocks including the assembly bias effect (although we consider the unrealistically-large amplitude of assembly bias effect). Even for the assembly bias mock, we demonstrate that the cosmological parameters can be recovered {it if} the analysis is restricted to scales $Rgtrsim 10~h^{-1}{rm Mpc}$. We also show that, by using a single population of source galaxies to infer the relative strengths of $Delta!Sigma$ for multiple lens samples at different redshifts, the joint probes method allows for self-calibration of photometric redshift errors and multiplicative shear bias. Thus we conclude that the emulator-based halo model method can be safely applied to the HSC-Y1 dataset, achieving a precision of $sigma(S_8)simeq 0.04$.
A variety of observations impose upper limits at the nano Gauss level on magnetic fields that are coherent on inter-galactic scales while blazar observations indicate a lower bound $sim 10^{-16}$ Gauss. Such magnetic fields can play an important astrophysical role, for example at cosmic recombination and during structure formation, and also provide crucial information for particle physics in the early universe. Magnetic fields with significant energy density could have been produced at the electroweak phase transition. The evolution and survival of magnetic fields produced on sub-horizon scales in the early universe, however, depends on the magnetic helicity which is related to violation of symmetries in fundamental particle interactions. The generation of magnetic helicity requires new CP violating interactions that can be tested by accelerator experiments via decay channels of the Higgs particle.
Persistent evidence for a cosmic hemispherical asymmetry in the temperature field of cosmic microwave background (CMB) as observed by both WMAP as well as PLANCK increases the possibility of its cosmological origin. Presence of this signal may lead to different values for the standard model cosmological parameters in different directions, and that can have significant implications for other studies where they are used. We investigate the effect of this cosmic hemispherical asymmetry on cosmological parameters using non-isotropic Gaussian random simulations injected with both scale dependent and scale independent modulation strengths. Our analysis shows that $A_s$ and $n_s$ are the most susceptible parameters to acquire position dependence across the sky for the kind of isotropy breaking phenomena under study. As expected, we find maximum variation arises for the case of scale independent modulation of CMB anisotropies. We find that scale dependent modulation profile as seen in PLANCK data could lead to only $1.25sigma$ deviation in $A_s$ in comparison to its estimate from isotropic CMB sky.
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