We propose using the upcoming Cosmic Microwave Background (CMB) ground based experiments to detect the signal of ALPs (Axion like particles) interacting with magnetic fields in galaxy clusters. The conversion between CMB photons and ALPs in the presence of the cluster magnetic field can cause a polarized spectral distortion in the CMB around a galaxy cluster. The strength of the signal depends upon the redshift of the galaxy cluster and will exhibit a distinctive spatial profile around it depending upon the structure of electron density and magnetic field. This distortion produces a different shape from the other known spectral distortions like $y$-type and $μ$-type and hence are separable from the multi-frequency CMB observation. The spectrum is close to kinematic Sunyaev-Zeldovich (kSZ) signal but can be separated from it using the polarization information. For the future ground-based CMB experiments such as Simons Observatory and CMB-S4, we estimate the measurability of this signal in the presence of foreground contamination, instrument noise and CMB anisotropies. This new avenue can probe the photon-ALP coupling over the ALP mass range from $10^{-13}$ eV to $10^{-12}$ eV with two orders of magnitude better accuracy from CMB-S4 than the current existing bounds.
In this paper, we consider a possibility that the temperature anisotropy of cosmic microwave background (CMB) is dominantly generated by the primordial fluctuations of QCD-axion like particles under a circumstance that inflaton's perturbation is too small to explain the CMB anisotropy. Since the axion potential is generated by acquiring its energy from radiation, the primordial fluctuations of the axion field generated in the inflation era are correlated with the CMB anisotropies. Consequently, the observations stringently constrain a model of the axion and the early universe scenario. The fol…
Axion-CMB scenario is an interesting possibility to explain the temperature anisotropy of the cosmic microwave background (CMB) by primordial fluctuations of the QCD axion \cite{Iso:2020pzv}. In this scenario, fluctuations of radiations are generated by an energy exchange between axions and radiations, which results in the correlation between the primordial axion fluctuations and the CMB anisotropies. Consequently, the cosmological observations stringently constrain a model of the axion and the early history of the universe. In particular, we need a large energy fraction $Ω_A^{}$ of the axion …
We explore the possible cosmological consequence of the gravitational coupling between the inflaton and axion-like fields. In view of the forthcoming cosmic microwave background (CMB) polarization and lensing data, we study the sensitivity of the CMB data on the cross-correlation between the curvature and axion isocurvature perturbations. Through a concrete example, we illustrate the explicit dependence of the scale dependent cross-correlation power spectrum on the axion parameters.
Axions and axion like particles are very attractive dark matter candidates. In this review, we briefly investigate how the cosmological observations reveal the existence of dark matter and some unique properties of axions/axion like particles which make them more interesting.
We point out two ways to search for low-mass axion dark matter using cosmic microwave background (CMB) polarization measurements. These appear, in particular, to be some of the most promising ways to directly detect fuzzy dark matter. Axion dark matter causes rotation of the polarization of light passing through it. This gives rise to two novel phenomena in the CMB. First, the late-time oscillations of the axion field today cause the CMB polarization to oscillate in phase across the entire sky. Second, the early-time oscillations of the axion field wash out the polarization produced at last-sc…
We revisit the cosmological constraints on resonant and non-resonant conversion of photons to axions in the cosmological magnetic fields. We find that the constraints on photon-axion coupling and primordial magnetic fields are much weaker than previously claimed for low mass axion like particles with masses $m_{\rm a} \lesssim 5\times 10^{-13}\,\text{eV}$. In particular we find that the axion mass range $10^{-14}\,\text{eV} \le m_{\rm a} \le 5\times 10^{-13}\,\text{eV}$ is not excluded by the CMB data contrary to the previous claims. We also examine the photon-axion conversion in the Galactic …
Axion-like particles are dark matter candidates motivated by the Peccei-Quinn mechanism and also occur in effective field theories where their masses and photon couplings are independent. We estimate the dispersion of circularly polarized photons in a background of oscillating axion-like particles (ALPs) with the standard $g_{aγ}\,a\,F_{μν}\tilde F^{μν}/4$ coupling to photons. This leads to birefringence or rotation of linear polarization by ALP dark matter. Cosmic microwave background (CMB) birefringence limits $Δα\lesssim (1.0)^\circ$ enable us to constrain the axion-photon coupling $g_{aγ} …
We examine the effects of photon-axion mixing on the CMB. We show that if there are very underdense regions between us and the last scattering surface which contain coherent magnetic fields (whose strength can be orders of magnitude weaker than the current bounds), then photon-axion mixing can induce observable deviations in the CMB spectrum. Specifically, we show that the mixing can give rise to non-thermal spots on the CMB sky. As an example we consider the well known CMB cold spot, which according to the Planck data has a weak distortion from a black body spectrum, that can be fit by our mo…
The existence of ultralight axion (ULA) with mass $\mathcal{O}( 10^{-26}\text{eV})$ is not favored by the CMB observations in the standard $Λ$CDM model. We show that the inclusion of early dark energy (EDE) will lift the CMB-lockdown on such ULA, and possibly other forms of dark matter beyond cold dark matter. By performing Monte Carlo Markov Chain analysis, it is found that, as opposed to $Λ$CDM, the AdS-EDE cosmology (with an Anti-de Sitter phase around recombination) now allows the existence of axion with mass $10^{-26}$ eV and predicts $6\%$ of the matter in our Universe to be such ULA, wh…
The polarization of Cosmic Microwave Background (CMB) photons is rotated as they pass through (ultralight-) axion string loops. Studying this birefringence can reveal valuable information about the axion-photon coupling and the structure of the string network. We develop an approximate analytic formalism and identify a kernel function that can be used to calculate the two-point correlation function for CMB birefringence induced by an arbitrary axion string network. Using this formalism, we evaluate the birefringence signal for some simple loop distributions (including scaling and network colla…
Axion-like particles (ALPs) can form a network of cosmic strings and domain walls that survives after recombination and leads to anisotropic birefringence of the cosmic microwave background (CMB). In addition to studying cosmic strings, we clarify and emphasize how the formation of ALP-field domain walls impacts the cosmic birefringence signal; these observations provide a unique way of probing ALPs with masses in the range $3H_0 \lesssim m_a \lesssim 3H_{\rm cmb}$. Using measurements of CMB birefringence from several telescopes, we find no evidence for axion-defect-induced anisotropic birefri…
We study axion strings of hyperlight axions coupled to photons. Hyperlight axions -- axions lighter than Hubble at recombination -- are a generic prediction of the string axiverse. These axions strings produce a distinct quantized polarization rotation of CMB photons which is $\mathcal{O}(α_{\rm em})$. As the CMB light passes many strings, this polarization rotation converts E-modes to B-modes and adds up like a random walk. Using numerical simulations we show that the expected size of the final result is well within the reach of current and future CMB experiments through the measurement of co…
The oscillation of the CMB photons into axions can cause CMB spectral distortion in the presence of large scale magnetic field. With the COBE limit on the $μ$ parameter and a homogeneous magnetic field with strength $B\lesssim 3.2$ nG at the horizon scale, an upper limit on the axion mass is found to be, $m_a\lesssim 4.8\times 10^{-5}$ eV for the KSVZ axion model. On the other hand, using the value of excluded axion mass $m_a\simeq 3.5\times 10^{-6}$ eV from the ADMX experiment together with the COBE bound on $μ$, is found $B\simeq 46$ nG for the KSVZ axion model and $B\simeq 130$ nG for DFSZ …
We study diffusion damping of acoustic waves in the photon-baryon fluid due to cosmic strings, and calculate the induced $μ$- and $y$-type spectral distortions of the cosmic microwave background. For cosmic strings with tension within current bounds, their contribution to the spectral distortions is subdominant compared to the distortions from primordial density perturbations.
We reconsider the effect of electromagnetic radiation from superconducting strings on cosmic microwave background (CMB) mu- and y-distortions and derive present (COBE-FIRAS) and future (PIXIE) constraints on the string tension, mu_s, and electric current, I. We show that absence of distortions of the CMB in PIXIE will impose strong constraints on mu_s and I, leaving the possibility of light strings (G mu_s < 10^{-18}) or relatively weak currents (I < 10 TeV).
Axion production due to photon-axion mixing in tangled magnetic field(s) prior to recombination epoch and magnetic field damping can generate cosmic microwave background (CMB) spectral distortions. In particular, contribution of both processes to CMB $μ$ distortion in the case of resonant photon-axion mixing is studied. Assuming that magnetic field power spectrum is approximated by a power law $P_B(k)\propto k^n$ with spectral index $n$, it is shown that for magnetic field cut-off scales $172.5$ pc $\leq λ_B\leq 4\times 10^3$ pc, axion contribution to CMB $μ$ distortion is subdominant in compa…
We exploit the complementarity among supersymmetry, inflation, axions, Big Bang Nucleosynthesis (BBN) and Cosmic Microwave Background Radiation (CMB) to constrain supersymmetric axion models in the light of the recent Planck and BICEP results. In particular, we derive BBN bounds coming from altering the light element abundances by taking into account hadronic and electromagnetic energy injection, and CMB constraints from black-body spectrum distortion. Lastly, we outline the viable versus excluded region of these supersymetric models that might account for the mild dark radiation observed.
The non-resonant conversion of Cosmic Microwave Background (CMB) photons into scalar as well as light pseudoscalar particles such as axion-like particles (ALPs) in the presence of turbulent magnetic fields can cause a unique, spatially fluctuating spectral distortion in the CMB. We use the publicly available Planck temperature maps for the frequency channels (70-545 GHz) to obtain the first ALP distortion map using $45\%$ clean part of the sky. The $95^{th}$ percentile upper limit on the RMS fluctuation of ALP distortions from the cleanest part of the CMB sky at $15$ arcmin angular resolution …
We calculate numerical solutions and analytic approximations for the intermediate-type spectral distortions. Detection of a μ-type distortion (saturated comptonization) in the CMB will constrain the time of energy injection to be at a redshift 2x10^6> z > 2x10^5, while a detection of a y-type distortion (minimal comptonization) will mean that there was heating of CMB at redshift z< 1.5x10^4. We point out that the partially comptonized spectral distortions, generated in the redshift range 1.5x10^4 < z x 2x10^5, are much richer in information than the pure y and μ-type distortions. The spectrum …
Measurements of cosmic microwave background (CMB) anisotropies provide strong evidence for the existence of dark matter and dark energy. They can also test its composition, probing the energy density and particle mass of different dark-matter and dark-energy components. CMB data have already shown that ultra-light axions (ULAs) with mass in the range $10^{-32}~{\rm eV} \to 10^{-26}~{\rm eV}$ compose a fraction $< 0.01$ of the cosmological critical density. Here, the sensitivity of a proposed CMB-Stage IV (CMB-S4) experiment (assuming a 1 arcmin beam and $< 1~μK{\rm-arcmin}$ noise levels over a…
We investigate the power spectrum of the distortion of Cosmic Microwave Background (CMB) due to the decay of the primordial magnetic fields. It is known that there are two-types of the CMB distortions, so-called μ- and y-types and we find that the signal of the y-type distortion becomes larger than that of the μ-type one. We also discuss cross power spectra between the CMB distortions and the CMB temperature anisotropy, which are naturally generated due to the existence of the primordial magnetic fields. We find that such cross power spectra have small amplitudes compared with the auto-power s…
Probing correlations among short and long-wavelength cosmological fluctuations is known to be decisive for deepening the current understanding of inflation at the microphysical level. Spectral distortions of the CMB can be caused by dissipation of cosmological perturbations when they re-enter Hubble after inflation. Correlating spectral distortions with temperature anisotropies will thus provide the opportunity to greatly enlarge the range of scales over which squeezed limits can be tested, opening up a new window on inflation complementing the ones currently probed with CMB and LSS. In this p…
Dark matter comprised of axion-like particles (ALPs) generated by the realignment mechanism in the post-inflationary scenario leads to primordial isocurvature fluctuations. The power spectrum of these fluctuations is flat for small wave numbers, extending to scales accessible with cosmological surveys. We use the latest measurements of Cosmic Microwave Background (CMB) primary anisotropies together with CMB lensing, Baryonic Acoustic Oscillations (BAO) and Sunyaev Zel'dovich (SZ) cluster counts to measure the amplitude and tilt of the isocurvature component. We find preference for a white-nois…
We examine bounds on adiabatic and isocurvature density fluctuations from $μ$-type spectral distortions of the cosmic microwave background (CMB). Studies of such distortion are complementary to CMB measurements of the spectral index and its running, and will help to constrain these parameters on significantly smaller scales. We show that a detection on the order of $μ\sim 10^{-7}$ would strongly be at odds with the standard cosmological model of a nearly scale-invariant spectrum of adiabatic perturbations. Further, we find that given the current CMB constraints on the isocurvature mode amplitu…
Light axions ($m_a \lesssim 10^{-10}$ eV) can form dense clouds around rapidly rotating astrophysical black holes via a mechanism known as rotational superradiance. The coupling between axions and photons induces a parametric resonance, arising from the stimulated decay of the axion cloud, which can rapidly convert regions of large axion number densities into an enormous flux of low-energy photons. In this work we consider the phenomenological implications of a superradiant axion cloud undergoing resonant decay. We show that the low energy photons produced from such events will be absorbed ove…
Axion-like particles (ALPs) rotate the linear polarization of photons through the ALP-photon coupling and convert the cosmic microwave background (CMB) $E$-mode to the $B$-mode. We derive the relation between the ALP dynamics and the rotation angle by assuming that the ALP $ϕ$ has a quadratic potential, $V=m^2ϕ^2/2$. We compute the current and future sensitivities of CMB observations to the ALP-photon coupling $g$, which can reach $g=4\times 10^{-21}\,\mathrm{GeV}^{-1}$ for $10^{-32}\,\mathrm{eV}\lesssim m\lesssim 10^{-28}\,\mathrm{eV}$ and extensively exceed the other searches for any mass $m…
Ultralight axions which couple sufficiently strongly to photons can leave imprints on the sky at diverse frequencies by mixing with cosmic light in the presence of background magnetic fields. We explore such direction dependent grey-body distortions of the CMB spectrum, enhanced by resonant conditions in the IGM plasma. We also find that if such axions are produced in the early universe and represent a subdominant dark radiation component today, they could convert into X-rays in supervoids, and brighten them at X-ray frequencies.
In string theory inspired models of axion-like fields, sub-leading non-perturbative effects, if sufficiently large, can introduce steep cliffs and gentle plateaus onto the underlying scalar potential. During inflation, the motion of a spectator axion $σ$ on this potential becomes temporarily fast, leading to localized amplification of one helicity state of gauge fields. In this model, the tensor and scalar correlators sourced by the vector fields exhibit localized peak(s) in momentum space corresponding to the modes that exit the horizon while the roll of $σ$ is fast. Thanks to the gravitation…
We propose a new mechanism of generating the $μ$ distortion in cosmic microwave background (CMB) originated from primordial gravitational waves. Such $μ$ distortion is generated by the damping of the temperature anisotropies through the Thomson scattering, even on scales larger than that of Silk damping. This mechanism is in sharp contrast with that from the primordial curvature (scalar) perturbations, in which the temperature anisotropies mainly decay by Silk damping effects. We estimate the size of the $μ$ distortion from the new mechanism, which can be used to constrain the amplitude of pri…
Models of inflation based on axions, which owe their popularity to the robustness against UV corrections, have also a very distinct class of signatures. The relevant interactions of the axion are a non-perturbative oscillating contribution to the potential and a shift-symmetric coupling to gauge fields. We review how these couplings affect the cosmological perturbations via a unified study based on the in-in formalism. We then note that, when the inflaton coupling to gauge fields is high enough to lead to interesting observational results, the backreaction of the produced gauge quanta on the i…
We give updated constraints on hypothetical light bosons with a two-photon coupling such as axions or axion-like particles (ALPs). We focus on masses and lifetimes where decays happen near big bang nucleosynthesis (BBN), thus altering the baryon-to-photon ratio and number of relativistic degrees of freedom between the BBN epoch and the cosmic microwave background (CMB) last scattering epoch, in particular such that $N_{\rm eff}^{\rm CMB} < N_{\rm eff}^{\rm BBN}$ and $η^{\rm CMB} < η^{\rm BBN}$. New constraints presented here come from Planck measurements of the CMB power spectrum combined with…
In this work we consider CMB spectral distortions as a probe of dark matter microphysics in the early universe. We demonstrate that future experiments such as PRISM have the potential to distinguish between scenarios which offer solutions to the small-scale problems of CDM cosmology.
Axions with mass greater than 0.7 eV are excluded by cosmological precision data because they provide too much hot dark matter. While for masses above 20 eV the axion lifetime drops below the age of the universe, we show that the cosmological exclusion range can be extended from 0.7 eV till 300 keV, primarily by the cosmic deuterium abundance: axion decays would strongly modify the baryon-to-photon ratio at BBN relative to the one at CMB decoupling. Additional arguments include neutrino dilution relative to photons by axion decays and spectral CMB distortions. Our new cosmological constraints …
We perform for the first time a dedicated analysis of cosmological constraints on DFSZ QCD axion models. Such constructions are especially interesting in light of the recent Xenon-1T excess and of hints from stellar cooling. In DFSZ models, for $m_a\gtrsim 0.1$ eV, scatterings of pions and muons can produce a sizable cosmic background of thermal axions, that behave similarly to massive neutrinos. However, the pion coupling depends on the alignment between the vevs of two Higgs doublets, and can be significantly suppressed or enhanced with respect to the KSVZ scenario. Using the latest Planck a…
CMB Constraints on Pre-Inflationary Axion Dark Matter Isocurvature
Harvard-Smithsonian Center for Astrophysics（哈佛-史密森天体物理中心）；Brown University（布朗大学）；CERN（欧洲核子研究组织）；Nanjing Normal University（南京师范大学）；University of Chinese Academy of Sciences（中国科学院大学）
The measurements of COBE/FIRAS have shown that the CMB spectrum is extremely close to a perfect blackbody. There are, however, a number of processes in the early Universe that should create spectral distortions at a level which is within reach of present day technology. In this talk, I will give a brief overview of recent theoretical and experimental developments, explaining why future measurements of the CMB spectrum will open up an unexplored window to early-universe and particle physics with possible non-standard surprises but also several guaranteed signals awaiting us.
Spectral Distortions from Axion Monodromy Inflation
Universidad Autónoma de Chiapas（奇亚帕斯自治大学）；Universidad de El Salvador（萨尔瓦多大学）；Consejo Nacional de Ciencia y Tecnología（国家科学技术委员会）；Instituto de Física, Universidad Nacional Autónoma de México（墨西哥国立自治大学物理研究所）
Some inflationary models predict the existence of isocurvature primordial fluctuations, in addition to the well known adiabatic perturbation. Such mixed models are not yet ruled out by available data sets. In this paper we explore the possibility of obtaining better constraints on the isocurva- ture contribution from future astronomical data. We consider the axion and curvaton inflationary scenarios, and use Planck satellite experimental specifications together with SDSS galaxy survey to forecast for the best parameter error estimation by means of the Fisher information matrix formal- ism. In …
Silk damping at redshifts 1.5 x 10^4 < z < 2 x 10^6 erases CMB anisotropies on scales corresponding to the comoving wavenumbers 8 < k < 10^4 Mpc^-1 (10^5 < \ell < 10^8). This dissipated energy is gained by the CMB monopole, creating distortions from a blackbody in the CMB spectrum of the μ-type and the i-type. We study, using Fisher matrices, the constraints we can get from measurements of these spectral distortions on the primordial power spectrum from future experiments such as Pixie, and how these constraints change as we change the frequency resolution and the sensitivity of the experiment…
We constrain the coupling of thermally-produced axion-like particles (here axions) with photons and gluons, using data from the cosmic microwave background (CMB) spectra and baryon acoustic oscillations. The axion possesses an explicit soft breaking mass term and it is produced thermally in the early Universe from either axion-photon or axion-gluon processes, accounting for the recent progresses in the field. We derive the most stringent bounds on the axion-gluon coupling to date on the mass range considered $10^{-4} \lesssim m_a/{\rm eV} \lesssim 100$, superseding the current bounds from SN19…
Measuring spectral distortions of the cosmic microwave background (CMB) is attracting considerable attention as a probe of high energy particle physics in the cosmological context, since PIXIE and PRISM have recently been proposed. In this paper, CMB distortions due to resonant conversions between CMB photons and light axion like particles (ALPs) are investigated, motivated by the string axiverse scenario which suggests the presence of a plenitude of light axion particles. Since these resonant conversions depend on the strength of primordial magnetic fields, constraints on CMB distortions can …
Prior to recombination, Silk damping causes the dissipation of energy from acoustic waves into the monopole of the Cosmic Microwave Background (CMB), resulting in spectral distortions. These can be used to probe the primordial scalar power spectrum on smaller scales than it is possible with CMB anisotropies. An enhancement of power on these scales is nevertheless required for the resulting distortions to be detectable by future experiments like PIXIE. In this paper, we examine all 49 single-field inflation models listed by Martin et al. in the Encyclopaedia Inflationaris [1] and find that only…
Spectral distortion of the cosmic microwave background provides a unique opportunity to probe primordial perturbations on very small scales by performing large-scale measurements. We discuss in a systematic and pedagogic way all the relevant physical phenomena involved in the production and evolution of the mu-type spectral distortion. Our main results agree with previous estimates (in particular we show that a recently found factor of 3/4 arises from relativistic corrections to the wave energy). We also discuss several subleading corrections such as adiabatic cooling and the effects of bulk v…
Distortions to the cosmic microwave background~(CMB) blackbody spectrum are calculated in the framework of cosmological perturbation theory. The second order Boltzmann equation is explicitly solved, with the spectral $y$ distortion and the frequency independent second order temperature perturbation. We also solve higher order Boltzmann equations systematically and find new type spectral distortions in the low energy limit of electrons. As an example, we concretely construct a solution to the cubic order Boltzmann equation and show that it can be characterized by three parameters: a cubic order…
