We present a novel scenario, in which light ($\sim$ few \rm{eV}) dark fermions (sterile neutrinos) interact with a scalar field like in mass varying neutrino dark energy theories. As the $\rm{eV}$ sterile states naturally become non-relativistic before the Matter Radiation Equality (MRE), we show that the neutrino-scalar fluid develops strong perturbative instability followed by the formation of neutrino-nuggets and the early dark energy behaviour disappears around MRE. The stability of the nugget is achieved when the Fermi pressure balances the attractive scalar force and we numerically find the mass and radius of heavy cold nuggets by solving for the static configuration for the scalar field. We find that for the case when DM nugget density is sub-dominant and most of the early DE energy goes into scalar field dynamics, it can in principle relax the Hubble anomaly. Especially when a kinetic energy dominated phase appears after the phase transition, the DE density dilutes faster than radiation and satisfy the requirements for solving $H_0$ anomaly. In our scenario, unlike in originally proposed early dark energy theory, the dark energy density is controlled by ($\rm{eV}$) neutrino mass and it does not require a fine tuned EDE scale. We perform a MCMC analysis and confront our model with Planck + SHOES and BAO data and find an evidence for non-zero neutrino-scalar EDE density during MRE. Our analysis shows that this model is in agreement of nearly 1.3$σ$ with SHOES measurement which is $H_0 = 74.03 \pm 1.42$ km/s/Mpc.
By means of a semiclassical analysis we show that the trace anomaly does not affect the cosmological constant. We calculate the evolution of the Hubble parameter in quasi de Sitter spacetime, where the Hubble parameter varies slowly in time, and in FLRW spacetimes. We show dynamically that a Universe consisting of matter with a constant equation of state, a cosmological constant and the quantum trace anomaly evolves either to the classical de Sitter attractor or to a quantum trace anomaly driven one. There is no dynamical effect that influences the effective value of the cosmological constant.
Technische Universität München（慕尼黑工业大学）；Nordita, KTH Royal Institute of Technology and Stockholm University（诺迪塔，皇家理工学院和斯德哥尔摩大学）；University of Southern Denmark（南丹麦大学）
The recently announced result by EDGES points an unexpected excess in the 21 cm global brightness temperature from cosmic dawn at $z\sim 17$, potentially indicating new phenomena beyond the $Λ$CDM model. A generic cosmological model which allows conformal and disformal couplings between dark matter and dark energy is employed to investigate the impact on the 21cm absorption signal and understand the EDGES anomaly. After exploring a wide range of parameter space for couplings, we find that the coupling effects can lead to a moderate change in the Hubble parameter while a negligible change in th…
We present a dark sector model addressing both the Hubble tension and the core-cusp problem. The model is based on a hidden Abelian gauge symmetry group with some chiral fermions required by the anomaly cancellation conditions, producing a candidate for the decaying fermion dark matter as a solution to the Hubble tension. Moreover, the sub-keV mass regime and the thermal history of the dark sector help the dark matter candidate resolve the core-cusp problem occurring in the standard $Λ$CDM cosmology.
Lensing amplitude anomaly and varying electron mass alleviate the Hubble and $S_8$ tensions
Key Laboratory of Dark Matter and Space Astronomy, Purple Mountain Observatory, Chinese Academy of Sciences（中国科学院紫金山天文台暗物质与空间天文重点实验室）；School of Astronomy and Space Science, University of Science and Technology of China（中国科学技术大学天文与空间科学学院）
Updated Cosmological Constraints in Extended Parameter Space with Planck PR4, DESI Baryon Acoustic Oscillations, and Supernovae: Dynamical Dark Energy, Neutrino Masses, Lensing Anomaly, and the Hubble Tension
本文在12参数扩展宇宙学模型中结合 Planck PR4、DESI BAO 和超新星数据更新了约束，发现暗能量动力学性质不稳健，中微子质量上限为0.3 eV，透镜异常不显著，哈勃张力未解决，$S_8$ 张力有所降低。
Self-interacting neutrinos that begin to free-stream at close to matter-radiation equality can reduce the physical size of photon sound horizon at last scattering surface. This mechanism can be the reason why standard $Λ$CDM cosmology sees a lower value of the Hubble constant than local measurements from distance ladder. We propose a new realization of self-interacting Dirac neutrinos (SID$ν$) with light-dark-photon mediator for a viable interaction mechanism. Our model is UV completed by a Dirac seesaw with anomaly-free dark $U(1)_X^{}$ gauge group which charges the right-handed neutrinos. Th…
We study the generation and evolution of magnetic field in the presence of chiral imbalance and gravitational anomaly which gives an additional contribution to the vortical current. The contribution due to gravitational anomaly is proportional to $T^2$ which can generate a seed magnetic field irrespective of plasma being hirally charged or neutral. We estimate the order of magnitude of the magnetic field to be $10^{30}$~G at $T\sim 10^9$ GeV, with a typical length scale of the order of $10^{-18}$ cm, which is much smaller than the Hubble radius at that temperature ($10^{-8}$ cm). Moreover, suc…
Recently anomalous flux in the cosmic optical background (COB) has been reported by the New Horizon observations. The COB flux is $16.37\pm 1.47\, \rm nW m^{-2} sr^{-1}$, at the LORRI pivot wavelength of $0.608\,\rm μm$, which is $\sim 4σ$ level above the expected flux from the Hubble Space Telescope (HST) galaxy count. It would be great if this were a hint for the eV scale dark matter decaying into photons. In this paper, we point out that such a decaying dark matter model predicts a substantial amount of anisotropy in the COB flux, which is accurately measured by the HST. The data of the HST…
Gravitational lens flux-ratio anomalies provide a powerful technique for measuring dark matter substructure in distant galaxies. However, before using these flux-ratio anomalies to test galaxy formation models, it is imperative to ascertain that the given anomalies are indeed due to the presence of dark matter substructure and not due to some other component of the lensing galaxy halo or to propagation effects. Here we present the case of CLASS~B1555+375, which has a strong radio-wavelength flux-ratio anomaly. Our high-resolution near-infrared Keck~II adaptive optics imaging and archival Hubbl…
Dark Acoustic Oscillations as an Early-Universe Explanation of the DESI Anomaly
Technische Universität München（慕尼黑工业大学）；Nordita, KTH Royal Institute of Technology and Stockholm University（诺迪塔，皇家理工学院与斯德哥尔摩大学）；University of Southern Denmark（南丹麦大学）
The standard cosmological paradigm narrates a reassuring story of a universe currently dominated by an enigmatic dark energy component. Disquietingly, its universal explaining power has recently been challenged by, above all, the $\sim4σ$ tension in the values of the Hubble constant. Another, less studied anomaly is the repeated observation of integrated Sachs-Wolfe imprints $\sim5\times$ stronger than expected in the $Λ$CDM model from R>100 $Mpc/h$ super-structures. Here we show that the inhomogeneous AvERA model of emerging curvature is capable of telling a plausible albeit radically differe…
We present new constraints on extended cosmological scenarios using the recent data from the Planck 2018 Legacy release. In addition to the six parameters of the standard LCDM model, we also simultaneously vary the dark energy equation of state, the neutrino mass, the neutrino effective number, the running of the spectral index and the lensing amplitude $A_L$. We confirm that a resolution of the Hubble tension is given by a dark energy equation of state with w<-1, ruling out quintessence models at high statistical significance. This solution is, however, not supported by BAO and Pantheon data.…
The Tajmar anomaly is an unexplained acceleration observed by gyroscopes close to, but isolated from, rotating rings cooled to 5K. The observed ratio between the gyroscope and ring accelerations was 3+/-1.2*10^-8 for clockwise rotations and about half this size for anticlockwise ones. Here, this anomaly is predicted using a new model that assumes that the inertial mass of the gyroscope is caused by Unruh radiation that appears as the ring and the fixed stars accelerate relative to it, and that this radiation is subject to a Hubble-scale Casimir effect. The model predicts that the sudden accele…
We notice that nearby galaxies having high negative peculiar velocities are distributed over the sky very inhomogeneously. A part of this anisotropy is caused by the "Local Velocity Anomaly", i.e. by the bulk motion of nearby galaxies away from the Local Void. But a half of the fast-flying objects reside within a small region RA = [11.5h, 13.0h], Dec. = [+20\circ, +40\circ], known as the Coma I cloud. According to Makarov & Karachentsev (2011), this complex contains 8 groups, 5 triplets, 10 pairs and 83 single galaxies with the total mass of 4.7\star10^13M\odot. We use 122 galaxies in the Coma…
Cosmology in Extended Parameter Space with DESI Data Release 2 Baryon Acoustic Oscillations: A 2$σ$+ Detection of Nonzero Neutrino Masses with an Update on Dynamical Dark Energy and Lensing Anomaly
Institute of Astronomy and Astrophysics, Academia Sinica（中央研究院天文及天文物理研究所）
In this paper, we explore in detail the cosmological implications of an abelian $L_μ-L_τ$ gauge extension of the Standard Model featuring a light and weakly coupled $Z'$. Such a scenario is motivated by the longstanding $\sim \, 4 σ$ discrepancy between the measured and predicted values of the muon's anomalous magnetic moment, $(g-2)_μ$, as well as the tension between late and early time determinations of the Hubble constant. If sufficiently light, the $Z'$ population will decay to neutrinos, increasing the overall energy density of radiation and altering the expansion history of the early uni…
The long-standing $4.2 \, σ$ muon $g-2$ anomaly may be the result of a new particle species which could also couple to dark matter and mediate its annihilations in the early universe. In models where both muons and dark matter carry equal charges under a $U(1)_{L_μ-L_τ}$ gauge symmetry, the corresponding $Z^\prime$ can both resolve the observed $g-2$ anomaly and yield an acceptable dark matter relic abundance, relying on annihilations which take place through the $Z^\prime$ resonance. Once the value of $(g-2)_μ$ and the dark matter abundance are each fixed, there is very little remaining freed…
Light new vector bosons can be produced gravitationally through quantum fluctuations during inflation; if these particles are feebly coupled and cosmologically metastable, they can account for the observed dark matter abundance. However, in minimal anomaly free $U(1)$ extensions to the Standard Model, these vectors generically decay to neutrinos if at least one neutrino mass eigenstate is sufficiently light. If these decays occur between neutrino decoupling and CMB freeze out, the resulting radiation energy density can contribute to $ΔN_{\rm eff}$ at levels that can ameliorate the Hubble tensi…
We consider a minimal extension of the Standard Model with a hidden sector charged under a dark local $U(1)'$ gauge group, accounting simultaneously for light neutrino masses and the observed Dark Matter relic abundance. The model contains two copies of right-handed neutrinos which give rise to light neutrino-masses via an extended seesaw mechanism. The presence of a stable Dark-Matter candidate and a massless state naturally arise by requiring the simplest anomaly-free particle content without introducing any extra symmetries. We investigate the phenomenology of the hidden sector considering …
An alternative to the postulate of dark energy required to explain the accelerated expansion of the universe is to adopt an inhomogeneous cosmological model to explain the supernovae data without dark energy. We adopt a void cosmology model, based on the inhomogeneous Lemaître-Tolman-Bondi solution of Einstein's field equations. The model can resolve observational anomalies in the $ΛCDM$ model, such as the discrepancy between the locally measured value of the Hubble constant, $H_0=73.24\pm 1.74\,{\rm km}\,{\rm s}^{-1}\,{\rm Mpc}^{-1}$, and the $H_0=66.93\pm 0.62\,{\rm km}\,{\rm s}^{-1}\,{\rm M…
Cosmological magnetic fields are being observed with ever increasing correlation lengths, possibly reaching the size of superclusters, therefore disfavouring the conventional picture of generation through primordial seeds later amplified by galaxy-bound dynamo mechanisms. In this paper we put forward a fundamentally different approach that links such large-scale magnetic fields to the cosmological vacuum energy. In our scenario the dark energy is due to the Veneziano ghost (which solves the $U(1)_A$ problem in QCD). The Veneziano ghost couples through the triangle anomaly to the electromagneti…
Is the $w_0w_a$CDM cosmological parameterization evidence for dark energy dynamics partially caused by the excess smoothing of Planck PR4 CMB anisotropy data?
Universidad de Granada（格拉纳达大学）；Jeonbuk National University（全北国立大学）；Kansas State University（堪萨斯州立大学）
