Neutrino Free Streaming Research Articles

Precision CMB constraints on eV-scale bosons coupled to neutrinos

The cosmic microwave background (CMB) has proven to be an invaluable tool for studying the properties and interactions of neutrinos, providing insight not only into the sum of neutrino masses but also the free streaming nature of neutrinos prior to recombination. The CMB is a particularly powerful probe of new eV-scale bosons interacting with neutrinos, as these particles can thermalize with neutrinos via the inverse decay process, nu bar{nu } rightarrow X, and suppress neutrino free streaming near recombination – even for couplings as small as lambda _{nu } sim {mathcal {O}}(10^{-13}). Here, we revisit CMB constraints on such bosons, improving upon a number of approximations previously adopted in the literature and generalizing the constraints to a broader class of models. This includes scenarios in which the boson is either spin-0 or spin-1, the number of interacting neutrinos is either N_{textrm{int}} = 1,2 or 3, and the case in which a primordial abundance of the species is present. We apply these bounds to well-motivated models, such as the singlet majoron model or a light U(1)_{L_{mu }-L_{tau }} gauge boson, and find that they represent the leading constraints for masses m_Xsim 1, {textrm{eV}}. Finally, we revisit the extent to which neutrino-philic bosons can ameliorate the Hubble tension, and find that recent improvements in the understanding of how such bosons damp neutrino free streaming reduces the previously found success of this proposal.

Implications on cosmology from Dirac neutrino magnetic moments

The mechanism for generating neutrino masses remains a puzzle in particle physics. If neutrino masses follow from a Dirac mass term, then neutrino states exist with opposite chirality compared to their weakly-interacting counterparts. These inactive states do not interact with their active counterparts at measurable scales in the standard model. However, the existence of these states can have implications for cosmology as they contribute to the radiation energy density at early times, and the matter energy density at late times. How Dirac neutrinos may populate thermal states via an anomalous magnetic moment operator is the focus of this work. A class of models where all neutrinos have a magnetic moment independent of flavor or chirality is considered. Subsequently, the cross sections for neutrinos scattering on background plasma particles are calculated so that the relic inactive neutrino energy is derived as a function of plasma temperature. To do so, one needs cross sections for scattering on all electrically charged standard-model particles. Therefore, the scattering cross section between a neutrino and $W$-boson via the magnetic moment vertex is derived. Current measurements put a constraint on the size of the neutrino magnetic moment from the cosmological parameter $N_{\rm eff}$ and light-element primordial abundances. Finally, how the extra Dirac states contribute to the matter energy density at late times is investigated by examining neutrino free-streaming.

Loop corrections to the power spectrum for massive neutrino cosmologies with full time- and scale-dependence

Loop corrections to the power spectrum are frequently computed using approximate non-linear kernels adopted from an Einstein de-Sitter (EdS) cosmology. We present an algorithm that allows us to take the full time- and scale-dependence of the underlying fluid dynamics into account, and apply it to assess the impact of neutrino free-streaming on the 1- and 2-loop matter power spectrum. Neutrino perturbations are described by a hybrid Boltzmann/two-fluid model, that we show to agree with the CLASS Boltzmann solution at the linear level when using an appropriate effective neutrino sound velocity. We then use this scheme at 1- and 2-loop to perform a precision comparison of the matter power spectrum with simplified treatments of massive neutrinos. For a commonly adopted scheme using cold dark matter+baryon perturbations and EdS kernels to compute non-linear corrections, we find deviations above 1% for k>0.15 h/Mpc at z=0, and sub-percent agreement on weakly non-linear scales at z=0.5. We also demonstrate the impact of the EdS approximation on the 2-loop power spectrum for massless neutrinos.

Neutrino puzzle: Anomalies, interactions, and cosmological tensions

New physics in the neutrino sector might be necessary to address anomalies between different neutrino oscillation experiments. Intriguingly, it also offers a possible solution to the discrepant cosmological measurements of $H_0$ and $\sigma_8$. We show here that delaying the onset of neutrino free-streaming until close to the epoch of matter-radiation equality can naturally accommodate a larger value for the Hubble constant $H_0=72.3 \pm 1.4$ km/s/Mpc and a lower value of the matter fluctuations $\sigma_8=0.786\pm 0.020$, while not degrading the fit to the cosmic microwave background (CMB) damping tail. We achieve this by introducing neutrino self-interactions in the presence of a non-vanishing sum of neutrino masses. This strongly interacting neutrino cosmology prefers $N_{\rm eff} = 4.02 \pm 0.29$, which has interesting implications for particle model-building and neutrino oscillation anomalies. We show that the absence of the neutrino free-streaming phase shift on the CMB can be compensated by shifting the value of other cosmological parameters, hence providing an important caveat to the detections made in the literature. Due to their impact on the evolution of the gravitational potential at early times, self-interacting neutrinos and their subsequent decoupling leave a rich structure on the matter power spectrum. In particular, we point out the existence of a novel localized feature appearing on scales entering the horizon at the onset of neutrino free-streaming. While the interacting neutrino cosmology provides a better global fit to current cosmological data, we find that traditional Bayesian analyses penalize the model as compared to the standard cosmological. Our analysis shows that it is possible to find radically different cosmological models that nonetheless provide excellent fits to the data, hence providing an impetus to thoroughly explore alternate cosmological scenarios.

The impact of baryonic physics and massive neutrinos on weak lensing peak statistics

ABSTRACT We study the impact of baryonic processes and massive neutrinos on weak lensing peak statistics that can be used to constrain cosmological parameters. We use the BAHAMAS suite of cosmological simulations, which self-consistently include baryonic processes and the effect of massive neutrino free-streaming on the evolution of structure formation. We construct synthetic weak lensing catalogues by ray tracing through light-cones, and use the aperture mass statistic for the analysis. The peaks detected on the maps reflect the cumulative signal from massive bound objects and general large-scale structure. We present the first study of weak lensing peaks in simulations that include both baryonic physics and massive neutrinos (summed neutrino mass Mν = 0.06, 0.12, 0.24, and 0.48 eV assuming normal hierarchy), so that the uncertainty due to physics beyond the gravity of dark matter can be factored into constraints on cosmological models. Assuming a fiducial model of baryonic physics, we also investigate the correlation between peaks and massive haloes, over a range of summed neutrino mass values. As higher neutrino mass tends to suppress the formation of massive structures in the Universe, the halo mass function and lensing peak counts are therefore modified as a function of Mν. Over most of the S/N range, the impact of fiducial baryonic physics is greater (less) than neutrinos for 0.06 and 0.12 (0.24 and 0.48) eV models. Both baryonic physics and massive neutrinos should be accounted for when deriving cosmological parameters from weak lensing observations.

Investigating the degeneracy between modified gravity and massive neutrinos with redshift-space distortions

There is a well known degeneracy between the enhancement of the growth of large-scale structure produced by modified gravity models and the suppression due to the free-streaming of massive neutrinos at late times. This makes the matter power-spectrum alone a poor probe to distinguish between modified gravity and the concordance ΛCDM model when neutrino masses are not strongly constrained. In this work, we investigate the potential of using redshift-space distortions (RSD) to break this degeneracy when the modification to gravity is scale-dependent in the form of Hu-Sawicki f(R). We find that if the linear growth rate can be recovered from the RSD signal, the degeneracy can be broken at the level of the dark matter field. However, this requires accurate modelling of the non-linearities in the RSD signal, and we here present an extension of the standard perturbation theory based model for non-linear RSD that includes both Hu-Sawicki f(R) modified gravity and massive neutrinos.

Sterile neutrinos with secret interactions—cosmological discord?

Several long-standing anomalies from short-baseline neutrino oscillation experiments—most recently corroborated by new data from MiniBooNE—have led to the hypothesis that extra, “sterile”, neutrino species might exist. Models of this type face severe cosmological constraints, and several ideas have been proposed to avoid these constraints. Among the most widely discussed ones are models with so-called “secret interactions” in the neutrino sector. In these models, sterile neutrinos are hypothesized to couple to a new interaction, which dynamically suppresses their production in the early Universe through finite-temperature effects. Recently, it has been argued that the original calculations demonstrating the viability of this scenario need to be refined. Here, we update our earlier results from \\arXivid{1310.6337} [JCAP 10 (2015) 011] accordingly. We confirm that much of the previously open parameter space for secret interactions is in fact ruled out by cosmological constraints on the sum of neutrino masses and on free-streaming of active neutrinos. We then discuss possible modifications of the vanilla scenario that would reconcile sterile neutrinos with cosmology.

Deconstructing the neutrino mass constraint from galaxy redshift surveys

The total mass of neutrinos can be constrained in a number of ways using galaxy redshift surveys. Massive neutrinos modify the expansion rate of the Universe, which can be measured using baryon acoustic oscillations (BAOs) or the Alcock-Paczynski (AP) test. Massive neutrinos also change the structure growth rate and the amplitude of the matter power spectrum, which can be measured using redshift-space distortions (RSD). We use the Fisher matrix formalism to disentangle these information sources, to provide projected neutrino mass constraints from each of these probes alone and to determine how sensitive each is to the assumed cosmological model. We isolate the distinctive effect of neutrino free-streaming on the matter power spectrum and structure growth rate as a signal unique to massive neutrinos that can provide the most robust constraints, which are relatively insensitive to extensions to the cosmological model beyond ΛCDM . We also provide forecasted constraints using all of the information contained in the observed galaxy power spectrum combined, and show that these maximally optimistic constraints are primarily limited by the accuracy to which the optical depth of the cosmic microwave background, τ, is known.

The separate and combined effects of baryon physics and neutrino free streaming on large-scale structure

We use the cosmo-OWLS and BAHAMAS suites of cosmological hydrodynamical simulations to explore the separate and combined effects of baryon physics (particularly feedback from active galactic nuclei, AGN) and free-streaming of massive neutrinos on large-scale structure. We focus on five diagnostics: i) the halo mass function; ii) halo mass density profiles; iii) the halo mass-concentration relation; iv) the clustering of haloes; and v) the clustering of matter; and we explore the extent to which the effects of baryon physics and neutrino free-streaming can be treated independently. Consistent with previous studies, we find that both AGN feedback and neutrino free-streaming suppress the total matter power spectrum, although their scale and redshift dependencies differ significantly. The inclusion of AGN feedback can significantly reduce the masses of groups and clusters, and increase their scale radii. These effects lead to a decrease in the amplitude of the mass-concentration relation and an increase in the halo autocorrelation function at fixed mass. Neutrinos also lower the masses of groups and clusters while having no significant effect on the shape of their density profiles (thus also affecting the mass-concentration relation and halo clustering in a qualitatively similar way to feedback). We show that, with only a small number of exceptions, the combined effects of baryon physics and neutrino free-streaming on all five diagnostics can be estimated to typically better than a few percent accuracy by treating these processes independently (i.e., by multiplying their separate effects).

Significance of neutrino-neutrino interaction in neutrino oscillation in core-collapse supernova

We study the possibility of neutrino-neutrino interaction inside the neutrino core of supernova (ρ ≥ 1010 g/cc) and outside the neutrinosphere. The angular dependence of the neutrino-neutrino interaction Hamiltonian causes multi-angle effects that can lead either to oscillation or free streaming of neutrinos. If the angle between interactions is π/2, the neutrinos are trapped inside neutrino core and chances of oscillation increases due to interaction. As the angle gradually changes, the chance of oscillation decreases and free streaming of neutrino can be observed out of core of supernova as shock waves.DOI: http://dx.doi.org/10.3126/bibechana.v12i0.11780 BIBECHANA 12 (2015) 89-95

Constraints on massive neutrinos from the CFHTLS angular power spectrum

We use the galaxy angular power spectrum at z ∼ 0.5–1.2 from the Canada-France-Hawaii-Telescope Legacy Survey Wide fields (CFHTLS-Wide) to constrain separately the total neutrino mass ∑mν and the effective number of neutrino species Neff. This survey has recently benefited from an accurate calibration of the redshift distribution, allowing new measurements of the (non-linear) matter power spectrum in a unique range of scales and redshifts sensitive to neutrino free streaming. Our analysis makes use of a recent model for the effect of neutrinos on the weakly non-linear matter power spectrum derived from accurate N-body simulations. We show that CFHTLS, combined with WMAP7 and a prior on the Hubble constant provides an upper limit of ∑mν < 0.29 eV and Neff = 4.17+1.62−1.26 (2 σ confidence levels). If we omit smaller scales which may be affected by non-linearities, these constraints become ∑mν < 0.41 eV and Neff = 3.98+2.02−1.20 (2 σ confidence levels). Finally we show that the addition of other large scale structures probes can further improve these constraints, demonstrating that high redshift large volumes surveys such as CFHTLS are complementary to other cosmological probes of the neutrino mass.

F(R) COSMOLOGY AND MASSIVE NEUTRINOS

f(R) gravity provides viable cosmology alternative to the ΛCDM model. We discuss the effect of massive neutrinos on matter power spectrum in this theory, to show that the anomalous growth of density fluctuations on small scales due to the scalaron force can be compensated by free streaming of neutrinos. As a result, models which predict observable deviation of the equation-of-state parameter w DE from w DE = -1 may be reconciled with observations of matter clustering if the total neutrino mass is O(0.5 eV ).

The effect of massive neutrinos on the matter power spectrum

We investigate the impact of massive neutrinos on the distribution of matter in the semi-non-linear regime (0.1<k<0.6 h/Mpc). We present a suite of large-scale N-body simulations quantifying the scale dependent suppression of the total matter power spectrum, resulting from the free-streaming of massive neutrinos out of high-density regions. Our simulations show a power suppression of 3.5-90 per cent at k~0.6 h/Mpc for total neutrino mass, m_nu=0.05-1.9 eV respectively. We also discuss the precision levels that future cosmological datasets would have to achieve in order to distinguish the normal and inverted neutrino mass hierarchies.

Matter Power Spectrum in f(R) Gravity with Massive Neutrinos

The effect of massive neutrinos on matter power spectrum is discussed in the context of $f(R)$ gravity. It is shown that the anomalous growth of density fluctuations on small scales due to the scalaron force can be compensated by free streaming of neutrinos. As a result, models which predict observable deviation of the equation-of-state parameter $w_\DE$ from $w_\DE=-1$ can be reconciled with observations of matter clustering if the total neutrino mass is $O(0.5 \eV)$.

The effect of neutrinos on the matter distribution as probed by the intergalactic medium

We present a suite of full hydrodynamical cosmological simulations that quantitatively address the impact of neutrinos on the (mildly non-linear) spatial distribution of matter and in particular on the neutral hydrogen distribution in the Intergalactic Medium (IGM), which is responsible for the intervening Lyman-α absorption in quasar spectra. The free-streaming of neutrinos results in a (non-linear) scale-dependent suppression of power spectrum of the total matter distribution at scales probed by Lyman-α forest data which is larger than the linear theory prediction by about 25 % and strongly redshift dependent. By extracting a set of realistic mock quasar spectra, we quantify the effect of neutrinos on the flux probability distribution function and flux power spectrum. The differences in the matter power spectra translate into a ∼ 2.5% (5%) difference in the flux power spectrum for neutrino masses with Σmν = 0.3 eV (0.6 eV). This rather small effect is difficult to detect from present Lyman-α forest data and nearly perfectly degenerate with the overall amplitude of the matter power spectrum as characterised by σ8. If the results of the numerical simulations are normalized to have the same σ8 in the initial conditions, then neutrinos produce a smaller suppression in the flux power of about 3% (5%) for Σmν = 0.6 eV (1.2 eV) when compared to a simulation without neutrinos. We present constraints on neutrino masses using the Sloan Digital Sky Survey flux power spectrum alone and find an upper limit of Σmν < 0.9 eV (2σ C.L.), comparable to constraints obtained from the cosmic microwave background data or other large scale structure probes.

Analytic spectra of CMB anisotropies and polarization generated by relic gravitational waves with modification due to neutrino free-streaming

We present an analytical calculation of the spectra of CMB anisotropies and polarizations generated by relic gravitational waves (RGWs). As a substantial extension to the previous studies, three new ingredients are included in this work. Firstly, the analytic $C_l^{TT}$ and $C_l^{TE}$ are given; especially the latter can be useful to extract signal of RGWs from the observed data in the zero multipole method. Secondly, a fitting formula of the decaying factor on small scales is given, coming from the visibility function around the photon decoupling. Thirdly, the impacts by the neutrino free-streaming (NFS) is examined, a process that occurred in the early universe and leaves observable imprints on CMB via RGWs. It is found that the analytic $C_l^{TT}$ and $C_l^{TE}$ have profiles agreeing with the numeric ones, except that $C^{TT}_l$ in a range $l \le 10$ and the $1^{st}$ trough of $C_l^{TE}$ around $l \sim 75$ have some deviations. With the new damping factor, the analytic $C^{EE}_l$ and $C^{BB}_l$ match with the numeric ones with the maximum errors only $\sim 3%$ up to the first three peaks for $l\le 600$, improving the previous studies substantially. The correspondence of the positions of peaks of $C^{XX}_l$ and those of RGWs are also demonstrated explicitly. We also find that NFS reduces the amplitudes of $C^{XX}_l$ by $(20% \sim 35%)$ for $l\simeq(100\sim 600)$ and shifts slightly their peaks to smaller angles. Detailed analyses show that the zero multipoles $l_0$, where $C_l^{TE}$ crosses 0, are shifted to larger values by NFS. This shifting effect is as important as those causedby different inflation models and different baryon fractions.

Analytic spectrum of relic gravitational waves modified by neutrino free streaming and dark energy

We include the effect of neutrino free streaming into the spectrum of relic gravitational waves (RGWs) in the currently accelerating universe. For the realistic case of a varying fractional neutrino energy density and a nonvanishing derivative of the mode function at the neutrino decoupling, the integro-differential equation of RGWs is solved by a perturbation method for the period from the neutrino decoupling to the matter-dominant stage. Incorporating it into the analytic solution of RGWs for the whole history of expansion of the universe, the analytic solution of RGWs is obtained, evolving from inflation up to the current acceleration. The resulting spectrum of RGWs covers the whole range of frequency $({10}^{\ensuremath{-}19}\char21{}{10}^{10})\text{ }\text{ }\mathrm{Hz}$ and improves the previous results. It is found that neutrino free streaming causes a reduction of the spectral amplitude by $\ensuremath{\sim}20%$ in the range $({10}^{\ensuremath{-}16}\char21{}{10}^{\ensuremath{-}10})\text{ }\text{ }\mathrm{Hz}$, and leaves the other portion of the spectrum almost unchanged. This agrees with the earlier numerical calculations. Examination is made on the difference between the accelerating and nonaccelerating models, and our analysis shows that the ratio of the spectral amplitude in the accelerating $\ensuremath{\Lambda}\mathrm{CDM}$ model over that in the CDM model is $\ensuremath{\sim}0.7$, and within the various accelerating models of ${\ensuremath{\Omega}}_{\ensuremath{\Lambda}}g{\ensuremath{\Omega}}_{m}$ the spectral amplitude is proportional to ${\ensuremath{\Omega}}_{m}/{\ensuremath{\Omega}}_{\ensuremath{\Lambda}}$ for the whole range of frequency. Comparison with LIGO S5 run sensitivity shows that RGWs are not yet detectable by the present LIGO, and in the future LISA may be able to detect RGWs in some inflationary models.

Lepton asymmetry in the primordial gravitational wave spectrum

Effects of neutrino free streaming are evaluated on the primordial spectrum of gravitational radiation taking both neutrino chemical potential and masses into account. The former or the lepton asymmetry induces two competitive effects, namely, to increase anisotropic stress, which damps the gravitational wave more, and to delay the matter-radiation equality time, which reduces the damping. The latter effect is more prominent and a large lepton asymmetry would reduce the damping. We may thereby be able to measure the magnitude of lepton asymmetry from the primordial gravitational wave spectrum.

Damping of tensor modes in cosmology

An analytic formula is given for the traceless transverse part of the anisotropic stress tensor due to free streaming neutrinos, and used to derive an integro-differential equation for the propagation of cosmological gravitational waves. The solution shows that anisotropic stress reduces the squared amplitude by 35.6% for wavelengths that enter the horizon during the radiation-dominated phase, independent of any cosmological parameters. This decreases the tensor temperature and polarization correlation functions for these wavelengths by the same amount. The effect is less for wavelengths that enter the horizon at later times. At the longest wavelengths the decrease in the tensor correlation functions due to neutrino free streaming ranges from 10.7% for ${\ensuremath{\Omega}}_{M}{h}^{2}=0.1$ to 9.0% for ${\ensuremath{\Omega}}_{M}{h}^{2}=0.15.$ An appendix gives a general proof that tensor as well as scalar modes satisfy a conservation law for perturbations outside the horizon, even when the anisotropic stress tensor is not negligible.

A three-dimensional hydrodynamic treatment of the hot dark matter cosmological scenario

view Abstract Citations (29) References (49) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Three-dimensional Hydrodynamic Treatment of the Hot Dark Matter Cosmological Scenario Cen, Renyue ; Ostriker, Jeremiah P. Abstract The evolution of the hot dark matter (HDM) model containing both baryonic matter and dark matter is computed for a postrecombination Friedmann-Robertson-Walker universe. We use a locally valid Newtonian approximation to model a representative piece of the universe with size much less than the horizon. A highly developed Eulerian hydrodynamic code is used (for a detailed methodological description see Cen 1992) for the gas with a standard particle-mesh (PM) code for the motion of collisionless dark matter particles. We model a standard HDM scenario (Bardeen et al. 1986), adopting the following set of parameters: h = 0.75, {OMEGA} = 1.0, {OMEGA}_b_ = 0.027, consistent with light- element nucleosynthesis (Walker et al. 1991; Schramm 1991). The simulation box size is L = 64 h^-1^ Mpc with 128^3^~10^6.3^ baryonic cells and an equal number of dark matter particles. The initial amplitude of the perturbation is fixed by the requirement that (δM/M)_rms_ = 1 on an 8 h^-1^ Mpc top-hat sphere at z = 0, which is consistent with recent COBE differential microwave radiometer measurements (cf. Wright et al. 1992). In addition to the dark matter, we follow separately six baryonic species (H, H^+^, He, He^+^, He^++^,e^-^) with allowance for both (nonequilibrium) collisional and radiative ionization in every cell. The background radiation field is followed in detail, with allowance made for bremsstrahlung and recombination radiation input as well as ionization losses. However, in computing the thermal changes of the gas, we allow for both line and continuum processes as well as Compton interactions with the cosmic microwave background radiation (CBR) and X-ray background radiation (XBR) fields. The final mean Sunyaev-Zel'dovich y-parameter is estimated to be y^bar^ = (3.2+/-1.6) x 10^-6^, below current attainable observations, with a rms fluctuation of approximately δy^bar^ = (3.6+/-1.8)x10^-6^ on arcminute scales and δT/T~1x10^-6^ on the COBE 7^deg^ scale. Of greater interest, this model can make a nontrivial (~10%) fraction of the XBR in the 1-10 keY range and does not produce overrich X-ray clusters (cf. Evrard & Davis 1988) as compared with observations. The model with our chosen parameters fails to produce enough ionization either by shocks or radiation (UV from stars not included in this simulation) to satisfy the Gunn-Peterson test (Gunn & Peterson 1965). It appears that for this model with low {OMEGA}_b_ only a very small fraction of the baryons (< 1%) will condense out as galaxies. This conclusion results from our input parameters (low {OMEGA}_b_, low amplitude) and is not in disagreement with prior work which found significant galaxy formation for larger values of these parameters. We also examine the relations among four kinds of objects: (1) initial high-density peaks, (2) galaxies, (3) final high-density peaks, and (4) bright X-ray spots. They show very interesting properties which are tightly related to the special feature of the HDM power spectrum: cutoff of short-wavelength power due to neutrino free streaming. We can set limits on ({OMEGA}_b_ amplitude) by the requirement that the 1 keV cosmic X-ray background not exceed its observed value and the distortion of the CBR not exceed COBE observations. The HDM models that other investigators (with high-resolution one-dimensional simulations) have found could successfully put over 10% of the baryons into galaxies are not permitted according to our calculations; they overproduce 1 keV X-rays and CBR distortions. Publication: The Astrophysical Journal Pub Date: November 1992 DOI: 10.1086/171930 Bibcode: 1992ApJ...399..331C Keywords: Astronomical Models; Baryons; Dark Matter; Hydrodynamic Equations; Three Dimensional Models; Boundary Conditions; Gas Dynamics; Particle Theory; X Ray Astronomy; Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: DARK MATTER; HYDRODYNAMICS full text sources ADS |