Ali Kaya
We show that the energy density of the superhorizon modes released in a non-Bunch-Davies vacuum can be arbitrarily large during inflation and it decreases like ln(a)/a^4 in the subsequent radiation dominated era. This may constitute a dark radiation component which can sufficiently alter the early cosmological evolution to alleviate the Hubble tension.
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For a standard $Λ$CDM universe with a power-law primordial power spectrum, the discrepancy between early- and late-universe measurements of the Hubble constant continued to grow and recently reached $5.3σ$. During inflation, local features in the inflationary potential often lead to band-limited features in the primordial power spectrum, hence breaking the power-law assumption in the derivation of the Hubble tension. We investigate whether such inflationary "glitches" can ease the Hubble tension. The recently released \emph{Planck} temperature and polarization data and the 2019 SH0ES+H0LiCOW j…
The inconsistent Hubble constant values derived from cosmic microwave background (CMB) observations and from local distance-ladder measurements may suggest new physics beyond the standard $Λ$CDM paradigm. It has been found in earlier works that, at least phenomenologically, non-standard recombination histories can reduce the $\gtrsim 4σ$ Hubble tension to $\sim 2σ$. Following this path, we vary physical and phenomenological parameters in RECFAST, the standard code to compute ionization history of the universe, to explore possible physics beyond standard recombination. We find that the CMB cons…
An early dark energy component consisting of a cosmic pseudo Nambu-Goldstone boson has been recently proposed to resolve the Hubble tension -- the four-sigma discrepancy between precision measurements of the expansion rate of the universe. Here we point out that such an axion-like component may be expected to couple to electromagnetism by a Chern-Simons term, and will thereby induce an anisotropic cosmic birefringence signal in the polarization of the cosmic microwave background (CMB). We show that observations of the rotation-angle power spectrum and cross-correlation with CMB temperature ani…
Multi-axion like description of the dark sector in light of the Hubble and $σ_8$ tensions
本文提出用多个耦合类轴子场描述暗区部分成分的概念验证模型，通过同时引入早期和晚期对$Λ$CDM的偏离，成功消除哈勃常数与$σ_8$张力，并与DESI巡天及BAO声学视界观测保持一致。
We show how a modified Friedmann equation, originating from a model of the universe built from a certain $W_3$ algebra, has the potential to explain the difference between the Hubble constants extracted from CMB data and from supernova data.
Allowing for a nonvanishing spin tensor for cold dark matter ($ω_{\mathrm{DM}}=0$) has the consequence of giving rise to an effective $\mathrm{FLRW}$ dynamics with a small negative barotropic constant for an effective dark matter density ($-1/3<ω_{\mathrm{eff}}\leq0$). This turns out to solve the Hubble parameter tension in a straightforward way.
We explore the possibility of using a gigaparsec-scale local void to reconcile the Hubble tension. Such a gigaparsec-scale void can be produced by multi-stream inflation where different parts of the observable universe follow different inflationary trajectories. The impact of such a void for cosmological observations is studied, especially those involving supernovae, Baryon Acoustic Oscillations (BAO) and the kinetic Sunyaev-Zel'dovich (kSZ) effect. As a benchmark model, a 1.7Gpc scale with boundary width 0.7Gpc and density contrast -0.14 may ease the Hubble tension.
We revisit D-term inflation with the bounds of the cosmic string tension from gravitational wave observations and consider the possible deviation of the spectral index compared with the $Λ$CDM model in light of prerecombination resolutions of the Hubble tension. D-term inflation requires very small coupling constants under these constraints. We show that natural coupling constants ($g=λ=0.1$) can be achieved in the case of D-term inflation on the brane.
Extended Uncertainty Principle: A Deeper Insight into the Hubble Tension?
本研究拓展海森堡不确定性原理应用于宇宙学的思路，引入含最小基本可测量动量的扩展不确定性原理作为量子引力大尺度效应候选框架，通过推导有效光子静质量与哈勃-勒梅特参数的关联，探究哈勃张力的成因并约束EUP长度尺度。
A current problem within the ΛCDM framework is the tension between late and early time measurements of the Hubble parameter today, H0. We entertain the possibility that dark energy modeled as multiple interacting axion-like-particle species can alleviate the current Hubble tension. We then test these parameters against the milder tension between the CMB and large scale structure (LSS) observations of σ8 to ensure that these models do not exacerbate the tension. We find that there exist parameter spaces for models of two and three axion-like-particles which can potentially alleviate the Hubble …
A new component added to the standard model of cosmology that behaves like a cosmological constant at early times and then dilutes away as radiation or faster can resolve the Hubble tension. We show that a rolling axion coupled to a non-Abelian gauge group exhibits the behavior of such an extra component at the background level and can present a natural particle-physics model solution to the Hubble tension. We compare the contribution of this bottom-up model to the phenomenological fluid approximation and determine that CMB observables sensitive only to the background evolution of the Universe…
Taking advantage of Gaussian process (GP), we obtain an improved estimate of the Hubble constant, $H_0=70.41\pm1.58$ km s$^{-1}$ Mpc$^{-1}$, using Hubble parameter [$H(z)$] from cosmic chronometers (CCH) and expansion rate function [$E(z)$], extracted from type Ia supernovae, data. We also use CCH data, including the ones with full covariance matrix, and $E(z)$ data to obtain a determination of $H_0=72.34_{-1.92}^{+1.90}$ km s$^{-1}$ Mpc$^{-1}$, which implies that the involvement of full covariance matrix results in higher values and uncertainties of $H_0$. These results are higher than those …
Alleviating the Hubble Tension with a Local Void and Transitions of the Absolute Magnitude
本文通过结合局部空洞和绝对星等跃迁，利用Pantheon+ SNIa样本及Planck 2018 CMB数据，有效缓解了局部与高红移观测间的哈勃张力，且观测数据强烈偏好ΛLTB空洞模型。
Holographic complexity and the Hubble tension: a quantum gravity portrayal for the large scale structure of the cosmos
本文提出通过量子引力视角，将哈勃常数与全息复杂度联系起来，以解决哈勃张力问题。
We consider the inverse Seesaw scenario for neutrino masses with the approximate Lepton number symmetry broken dynamically by a scalar with Lepton number two. We show that the Majoron associated to the spontaneous symmetry breaking can alleviate the Hubble tension through its contribution to $ΔN_\text{eff}$ and late decays to neutrinos. Among the additional fermionic states required for realizing the inverse Seesaw mechanism, sterile neutrinos at the keV-MeV scale can account for all the dark matter component of the Universe if produced via freeze-in from the decays of heavier degrees of freed…
The tension between early and late Universe probes of the Hubble constant has motivated various new FLRW cosmologies. Here, we reanalyse the Hubble tension with a recent age of the Universe constraint. This allows us to restrict attention to matter and a dark energy sector that we treat without assuming a specific model. Assuming analyticity of the Hubble parameter $H(z)$, and a generic low redshift modification to flat $Λ$CDM, we find that low redshift data ($z \lesssim 2.5$) and well-motivated priors only permit a dark energy sector close to the cosmological constant $Λ$. This restriction ru…
Gravitational particle production, the cosmological tensions and fast radio bursts
本文修正了引力真空极化对哈勃常数的影响，并探讨其对σ₈张力和快速射电暴测量的贡献，表明引力真空极化不缓解σ₈张力但缓解哈勃张力。
Resolving the Hubble tension with Early Dark Energy
本文通过频率派剖面似然分析规避先验体积效应，结合Planck、BOSS、DES和SH0ES数据约束EDE，证明EDE可将$H_0$提升至与SH0ES相符，是缓解哈勃张力的可行方案。
We present a kinetically mixed dark sector (KMIX) model to address the Hubble and $S_8$ tensions. Inspired from string theory, our model includes two fields: an axion, which plays a role similar to the scalar field in early dark energy models, and a dilaton. This theory differs from other axio-dilaton models aimed at the Hubble tension in that there is necessarily kinetic mixing between the two fields which allows for efficient energy transfer from the axion into the dilaton which has $w\approx1$. As a direct consequence of these dynamics, we find the model does not need to resort to a fine-tu…
Gravitational particle production and the Hubble tension
本文研究了标量粒子的引力粒子产生效应对宇宙能量密度的影响，发现该效应会增加直接测量的哈勃常数$H_0$值，可能解释局部与非局部测量的差异，从而缓解哈勃张力。
In prerecombination resolutions of the Hubble tension, such as early dark energy, new physics before recombination shifts the values of relevant cosmological parameters so that the models can fit with cosmic microwave background and baryon acoustic oscillations observations as well as $Λ$CDM does. In this paper, we clarify how the parameter shifts are related with $δH_0$, particularly we find the shift of primordial scalar spectral index scales as ${δn_s}\simeq 0.4{δH_0\over H_0}$ by performing the Monte Carlo Markov chain analysis with the Planck2018+BAO+Pantheon+R19+Keck Array/BICEP dataset.…
Dark energy era with a resolution of Hubble tension in generalized entropic cosmology
本文提出基于四参数广义熵的暗能量模型，通过推广表观视界熵描述宇宙热历史，并在特定参数下给出更高哈勃常数，从而为缓解哈勃张力提供可行方案。
We show that the cosmic bulk viscosity estimated in our previous works is sufficient to bridge the $H_0$ value inferred from observations of the early universe with the value inferred from the local (late) universe.
The discrepancy between early-Universe inferences and direct measurements of the Hubble constant, known as the Hubble tension, recently became a pressing subject in high precision cosmology. As a result, a large variety of theoretical models have been proposed to relieve this tension. In this work we analyze a conformally-coupled modified gravity (CCMG) model of an evolving gravitational constant due to the coupling of a scalar field to the Ricci scalar, which becomes active around matter-radiation equality, as required for solutions to the Hubble tension based on increasing the sound horizon …
Hubble tension is routinely presented as a mismatch between the Hubble constant $H_0$ determined locally and a value inferred from the flat $Λ$CDM cosmology. In essence, the tension boils down to a disagreement between two numbers. Here, assuming the tension is cosmological in origin, we predict that within flat $Λ$CDM there should be other inferred values of $H_0$, and that a "running of $H_0$ with redshift" can be expected. These additional determinations of $H_0$ may be traced to a difference between the effective equation of state (EoS) of the Universe within the Friedmann-Lemaître-Roberts…
Recently, it has been found that complete resolution of the Hubble tension might point to a scale-invariant Harrison-Zeldovich spectrum of primordial scalar perturbation, i.e. $n_s=1$ for $H_0\sim 73$km/s/Mpc. We show that for well-known slow-roll models, if inflation ends by a waterfall instability with respect to another field in the field space while inflaton is still at a deep slow-roll region, $n_s$ can be lifted to $n_s= 1$. A surprise of our result is that with pre-recombination early dark energy, chaotic $ϕ^2$ inflation, ruled out by Planck+BICEP/Keck in standard $Λ$CDM, can be revived…
Towards a possible solution to the Hubble tension with Horndeski gravity
本文在Horndeski引力框架下构建暗能量模型，通过自相互作用和非最小耦合实现低红移幻影行为及高红移负能量密度，以缓解哈勃张力，并验证其稳定性及与观测数据的契合。
Guide for the Hubble Tension: Mid-Time Solutions and Generalized PAge Parameterizations
该研究针对哈勃张力，提出广义PAge参数化，结合晚期与CMB观测数据，发现中期新物理或为解决哈勃张力的关键，且相关模型优于标准ΛCDM。
In recent years the discrepancy in the value of the Hubble parameter has been growing. Recently, there are works supporting the proposal that the uncertainty principles can solve the Hubble tension. Motivated by this proposal, we work with an isotropic and homogeneous FRW universe, obtain its Hamiltonian equations, and thus, the Hubble parameter through the first Friedmann equation. In the context of GUP and EUP models, the Hubble parameter is modified. Since the fingerprints of quantum gravity are imprinted on the CMB, we consider the GUP/EUP-modified Hubble parameter in the first Friedmann e…
Acceleration of the Universe without the Hubble tension with Kaniadakis holographic dark energy using the Hubble horizon as the IR cut-off
本文提出以哈勃视界为红外截断、含一阶 Kaniadakis 熵的全息暗能量模型，利用超新星与哈勃数据约束参数，得到 $H_0=72.8$ 并缓解哈勃张力。
The Dilaton: A Natural Resolution to the Hubble Tension via Spontaneous Scale Symmetry Breaking
稀释子通过自发尺度对称性破缺自然解决哈勃张力，产生所需的晚期方程状态演变并保护场质量。
We consider a low redshift $(z<0.7)$ cosmological dataset comprising megamasers, cosmic chronometers, type Ia SNe and BAO, which we bin according to their redshift. For each bin, we read the value of $H_0$ by fitting directly to the flat $Λ$CDM model. Doing so, we find that $H_0$ descends with redshift, allowing one to fit a line with a \textit{non-zero} slope of statistical significance $2.1 \, σ$. Our analysis rests on the use of cosmic chronometers to break a degeneracy in BAO data and it will be imperative to revisit this feature as data improves. Nevertheless, our results provide the firs…
The $Λ$CDM model provides a good fit to most astronomical observations but harbors large areas of phenomenology and ignorance. With the improvements in the precision and number of observations, discrepancies between key cosmological parameters of this model have emerged. Among them, the most notable tension is the 4$σ$ to 6$σ$ deviation between the Hubble constant ($H_{0}$) estimations measured by the local distance ladder and the cosmic microwave background (CMB) measurement. In this review, we revisit the $H_{0}$ tension based on the latest research and sort out evidence from solutions to th…
We consider some background tests of standard cosmology in the context of Horava gravity with different scaling dimensions for space and time, which has been proposed as a renormalizable, higher-derivative, Lorentz-violating quantum gravity model without ghost problems. We obtain the "very strong" and "strong" Bayesian evidence for our two cosmology models A and B, respectively, depending on the choice of parametrization based on Horava gravity, against the standard, spatially-flat, LCDM cosmology model based on general relativity. An MCMC analysis with observational data, including BAO, shows…
Impact of the Hubble tension on the $r$-$n_s$ contour
本文利用最新CMB、BAO和SN数据研究早期暗能量对暴胀参数的影响，证实其会推动$n_s$趋近1并收紧$r$上限，并探讨未来CMB-S4和LiteBIRD实验对暴胀模型的区分能力。
Anti-de Sitter (AdS) vacua, being theoretically important, might have an unexpected impact on the observable universe. We find that in early dark energy (EDE) scenarios the existence of AdS vacua around recombination can effectively lift the CMB-inferred $H_0$ value. As an example, we study a phenomenological EDE model with an AdS phase starting at the redshift $z\sim2000$ and ending shortly after recombination (hereafter the universe will settle down in a $Λ>0$ phase until now), and obtain a best-fit $H_0=72.74$ km/s/Mpc without degrading the CMB fit compared with the standard $Λ$CDM model.
Revisiting the Hubble tension with an inverse power-law early dark energy
该研究提出带逆幂律渐近尾部势的新型早期暗能量模型，拟合CMB+BAO+SN+H0DN数据集得到H0相关值，可通过未来CMB和物质功率谱数据检验，还讨论了模型的精细调节问题以缓解哈勃张力。
Partial Relief of the Hubble Tension and a Natural Self-Interacting Dark Matter Candidate From Staged Symmetry Breaking
通过暗部门中的自发对称破缺触发暗物质子成分衰变，部分缓解哈勃张力并产生自相互作用暗物质候选者。
The Hubble tension as an effect of the renormalization of fundamental constants and cosmological parameters
本文提出用 $G$、$Λ$ 等基本常数和宇宙学参数的尺度跑动解释哈勃张力，认为 CMB 与超新星测得的不同 $H_0$ 源于探测尺度差异。
Testing the coupling of dark radiations in light of the Hubble tension
本文研究自相互作用暗辐射对宇宙演化及哈勃张力的影响，通过混合或不混合自由流动暗辐射的情形分析$H_0$约束，并利用Fisher方法预测Planck、AliCPT与CMB-S4联合测量可达7.64σ。
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