arXiv subjects

Yo Toda

Publications and source records attributed to Yo Toda.

15 recordsLinked to original sources

arXiv2026

Signatures of Modified Gravity on Linear Scales in a Dynamical Dark Energy Background

Cosmological data from the cosmic microwave background (CMB), baryon acoustic oscillations, and Type Ia supernovae suggest that the component driving the accelerated expansion of the Universe may be dynamical at the $\sim 2.5$-$3\sigma$ CL. The best-fit CPL model produces a level of cosmic structure similar to that of $\Lambda$CDM, with both models exhibiting mild tension with redshift-space distortion data. In this {\it Letter}, we parametrize possible departures of the effective gravitational coupling from Newton's constant in the late Universe, below a comoving scale $\lambda_c$, using two redshift bins, $0 \leq z < 1$ and $1 \leq z \leq 3$. We then determine the optimal values of $\lambda_c$ and the amplitude of these deviations from General Relativity, assuming a background with dynamical dark energy in CPL form. We find that, in order to achieve the required suppression of structure growth at low redshifts while remaining consistent with CMB constraints -- primarily from the late-time ISW effect at low $\ell$ and lensing at high $\ell$ -- we must require modified gravity effects to have a characteristic scale of $\lambda_c \lesssim 150\,\mathrm{Mpc}$ (95\% CL). This places the relevant scales squarely within the range probed by galaxy surveys. The best-fit value is $\lambda_c \simeq 40\,\mathrm{Mpc}$, well below the 95\% CL upper limit. Using Planck PR4, DESI DR2, Pantheon+ (or DES-Dovekie) and redshift-space distortions data we confirm that a CPL background with standard gravity is moderately preferred over $\Lambda$CDM; this preference strengthens to a mildly strong level when modified gravity effects are included. This enhancement leaves the CPL parameters largely unchanged, but shifts them slightly further into the quintom region.

astro-ph.CO↗

arXiv2026

Hamilton-Jacobi Approach to Inflationary Scenarios through Extended Entropies: An Observational Perspective

The slow-roll inflation paradigm can be systematically generalized within the framework of non-standard entropy formalisms, giving rise to a broad class of inflationary models that deviate from the conventional Bekenstein--Hawking case. We adopt a pragmatic observational strategy, employing the Hamilton--Jacobi formalism to establish a direct link between the inflationary potential, the generalized entropy function, and the resulting cosmological observables. In this approach we introduce a novel non-linear parametrization of the Hubble parameter, yielding sensible results, including consistency with recent observational data and new estimates of the cosmological parameters of the generalized entropy framework: the Tsallis parameter $\delta\simeq1.1-1.2$, the R\'enyi parameter $\alpha\sim\mathcal{O}(10^{-14})$, and the Kaniadakis statistics parameter $K\sim\mathcal{O}(10^{-17})$. Our analysis proceeds in two regimes: first, by constraining models directly with the primary inflationary parameters including the scalar spectral index ($n_s$) and the tensor-to-scalar ratio ($r$); second, by exploring the impact of the observational uncertainty on the upper bound of $r$ ($\sigma_r$), which we vary to assess its influence on parameter estimation. This dual approach yields complementary posterior distributions that restrict the viable parameter space of entropy-based inflationary models. We further highlight the implications of the Hamilton--Jacobi method for the dynamics of the inflationary epoch, the reheating process, and, as a secondary objective, the subsequent evolution of cosmic structure in the late universe.

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arXiv2025

Constraints on the varying electron mass and early dark energy in light of ACT DR6 and DESI DR2 and the implications for inflation

Primarily motivated by the Hubble tension, we analyze the varying electron mass model and axionlike early dark energy model (EDE) using baryon acoustic oscillation data from DESI DR2 data and including the recent results from ACT DR6. Our analysis indicates that $m_{e} / m_{e0} = 1.0081 \pm 0.0046 $ and the energy fraction of EDE is constrained as $f_\mathrm{EDE} < 0.016$. Since those cosmological models fit with different spectral index $n_s$, we show the posterior of those models on the ($n_s-r$) plane and point out that, for example, Starobinsky inflation works for varying electron mass model while the standard supersymmetric hybrid inflation is preferred in the EDE model.

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arXiv2025

Constraints on the simultaneous variation of the fine structure constant and electron mass in light of DESI BAO data

We study the cosmological constraints of the time variation of the electron mass $m_e$ and the fine-structure constant $\alpha$, using data of cosmic microwave background, supernovae light curve and baryon acoustic oscillation (BAO) data including the recent DESI BAO DR2 measurements. The results are slightly depending on the BAO data set included in the analysis. The latest DESI BAO DR2 data strongly indicates that $m_e$ or $\alpha$ is slightly larger than the previous data from 6DF+SDSS and DESI BAO DR1. We also compare the varying $m_e$ model, the varying $\alpha$ model, and the simultaneous variation of $m_e$ and $\alpha$. When considering the Hubble tension, a larger electron mass is the most promising option and the variation of the fine-structure constants does not alleviate the tension.

astro-ph.CO↗

arXiv2024

Redshift-space distortion constraints on the neutrino mass and models to alleviate the Hubble tension

We discuss the neutrino mass and Hubble tension solutions and examine their effects on the redshift-space distortion (RSD) observations. An analysis with RSD data indicates smaller amplitude of perturbation. Including RSD data results in a slightly weaker upper limit on the neutrino mass than that derived for data without RSD, which is common in other extended models too. We have evaluated the impacts of RSD observations on some extended models, including the varying electron mass model, a time-dependent dark energy model with two parameter equations of state (EOS), and a model where the number of neutrino species is free. When we estimate the cosmological parameters for data including RSD, we found that the EOS parameter for dark energy is larger than that of the cosmological constant, and the effective number of neutrino species is smaller than the standard value, which infers a smaller present Hubble parameter $H_0$. From the viewpoint of cosmological tensions, the varying electron mass model with nonzero neutrino mass option looks promising to relax the Hubble tension and the $S_8$ tension simultaneously.

astro-ph.CO↗

arXiv2024

Efficient Compression of Redshift-Space Distortion Data for Late-Time Modified Gravity Models

Current cosmological observations allow for deviations from the standard growth of large-scale structures in the universe. These deviations could indicate modifications to General Relativity on cosmological scales or suggest the dynamical nature of dark energy. It is important to characterize these departures in a model-independent manner to understand their significance objectively and explore their fundamental causes more generically across a wider spectrum of theories and models. In this paper, we compress the information from redshift-space distortion data into 2-3 parameters $\mu_i$, which control the ratio between the effective gravitational coupling in Poisson's equation and Newton's constant in several redshift bins in the late universe. We test the efficiency of this compression using mock final-year data from the Dark Energy Spectroscopic Instrument (DESI) and considering three different models within the class of effective field theories of dark energy. The constraints on the parameters of these models, obtained from both the direct fit to the data and the projection of the compressed parameters onto the parameters of the models, are fully consistent, demonstrating the method's good performance. Then, we apply it to current data and find hints of a suppressed matter growth in the universe at $\sim 2.7\sigma$ C.L., in full accordance with previous works in the literature. Finally, we perform a forecast with DESI data and show that the uncertainties on the parameters $\mu_1$ at $z<1$ and $\mu_2$ at $1<z<3$ are expected to decrease by approximately $40\%$ and $20\%$, respectively, compared to those obtained with current data. Additionally, we project these forecasted constraints onto the parameters of the aforesaid models.

astro-ph.CO↗

arXiv2024

Combining pre- and post-recombination new physics to address cosmological tensions: case study with varying electron mass and sign-switching cosmological constant

It has recently been argued that the Hubble tension may call for a combination of both pre- and post-recombination new physics. Motivated by these considerations, we provide one of the first concrete case studies aimed at constructing such a viable combination. We consider models that have individually worked best on either end of recombination so far: a spatially uniform time-varying electron mass leading to earlier recombination (also adding non-zero spatial curvature), and a sign-switching cosmological constant inducing an AdS-to-dS transition within the $\Lambda_{\rm s}$CDM model. When confronted against Cosmic Microwave Background (CMB), Baryon Acoustic Oscillations, and Type Ia Supernovae data, we show that no combination of these ingredients can successfully solve the Hubble tension. We find that the matter density parameter $\Omega_m$ plays a critical role, driving important physical scales in opposite directions: the AdS-to-dS transition requires a larger $\Omega_m$ to maintain the CMB acoustic scale fixed, whereas the varying electron mass requires a smaller $\Omega_m$ to maintain the redshift of matter-radiation equality fixed. Despite the overall failure, we use our results to draw general model-building lessons, highlighting the importance of assessing tension-solving directions in the parameter space of new physics parameters and how these correlate with shifts in other standard parameters, while underscoring the crucial role of $\Omega_m$ in this sense.

astro-ph.CO↗

arXiv2024

DESI constraints on the varying electron mass model and axion-like early dark energy

Baryon acoustic oscillation (BAO) is one of the important standard rulers in cosmology. The results of the latest BAO measurements by Dark Energy Spectroscopic Instrument (DESI) survey have been reported. Cosmology with the varying electron mass model and the early dark energy models are regarded as interesting models to resolve the Hubble tension. We present constraints on the varying electron mass model and early dark energy models in new DESI data as well as cosmic microwave background by Planck and the conventional BAO data from 6dF, MGS, and DR12 and supernovae light curve data into analysis. Since new DESI BAO data indicate a slightly longer sound horizon $r_dh$ than the other BAO observations, for the varying electron mass model, the larger $H_0 =69.44\pm 0.84 $ km$/$s$/$Mpc is indicated.

astro-ph.CO↗

arXiv2023

Constraints on sterile neutrinos and the cosmological tensions

We investigate cosmological bounds on sterile neutrino masses in the light of the Hubble and $S_8$ tensions. We argue that non-zero masses for sterile neutrinos are inferred at 2$\sigma$ level in some extended models such as varying dark energy equation of state, when a direct measurement of the Hubble constant $H_0$ and weak lensing measurement of dark energy survey (DES) are taken into account. Furthermore, the Hubble and $S_8$ tensions are also reduced in such a framework. We also consider the case where a non-flat Universe is allowed and show that a slightly open Universe may be favored in models with sterile neutrinos in the context of the cosmological tensions.

astro-ph.CO↗

arXiv2023

Impact of big bang nucleosynthesis on the H0 tension

We investigate the impact of big bang nucleosynthesis (BBN) on the Hubble tension, focusing on how the treatment of the reaction rate and observational data affect the evaluation of the tension. We show that the significance of the tension can vary by $0.8 \sigma$ in some early dark energy model, depending on the treatment of the reaction rate and observational data. This indicates that how we include the BBN data in the analysis can give a significant impact on the Hubble tension, and we need to carefully consider the assumptions of the analysis to evaluate the significance of the tension when the BBN data is used.

astro-ph.CO↗

arXiv2023

Variation of the fine structure constant in the light of recent helium abundance measurement

We point out that the recent result of primordial helium-4 ($^4$He) abundance measurement by EMPRESS, which has reported a smaller $^4$He abundance than other measurements, can be well fitted by assuming a time-variation of the fine structure constant $\alpha$ which is slightly smaller than the present value during big bang nucleosynthesis (BBN). We find that the EMPRESS result in combination with deuterium abundance measurement indicates $-2.6\% <\Delta\alpha/\alpha <-1.4 \%$ (68\% C.L.) where $\Delta \alpha$ is the difference between the values of $\alpha$ at the BBN and present epochs, while $-1.2\% <\Delta\alpha/\alpha <0.4 \%$ (68\% C.L.) is obtained from other previous $^4$He abundance data. We also investigate its effects in the framework where the effective number of neutrino species and the lepton asymmetry, which are other typical interpretations of the EMPRESS result, are allowed to vary. Once a smaller $\alpha$ is adopted, the EMPRESS result can be explained without assuming any non-standard values for the effective number of neutrino species and lepton asymmetry.

astro-ph.CO↗

arXiv2022

Big Bang Nucleosynthesis constraints on varying electron mass solution to the Hubble tension

A cosmological model with a time-varying mass of electrons seems a promising solution for the so-called Hubble tension. We examine the big bang nucleosynthesis (BBN) constraints on the time-varying electron mass model, because a larger electron mass gives rise to the smaller neutron decay rate which could affect the light element abundance. Additionally, different inferred cosmological parameters, primarily baryon asymmetry, to keep the cosmic background power spectrum unchanged could affect the abundance of light element. We find that the predicted helium fraction becomes larger and the deuterium abundance becomes smaller as the electron mass at the BBN time becomes larger. Thus, we conclude that an acceptable electron mass at the BBN time would be only approximately 1% greater than the current electron mass.

astro-ph.CO↗

arXiv2022

Electron mass variation from dark sector interactions and compatibility with cosmological observations

We investigate the model where electrons and dark matter interact with dark energy through the rolling of a scalar field which comes from extra dimensional theories such as the braneworld theory and Brans-Dicke theory. In this model, dark energy couples to dark matter and electrons, which leads to larger values of the mass energies of dark matter and electrons in the early universe. We also fit our model to the cosmological data. By analyzing the data from Planck, baryon acoustic oscillation (BAO), light curves (Pantheon), and type-Ia supernovae (SH0ES), it can be seen that the Hubble tension is relieved in our model and the coupling parameter prefers a non-zero value with a significance of over 2{\sigma}.

astro-ph.CO↗

arXiv2021

Comparing early dark energy and extra radiation solutions to the Hubble tension with BBN

The shorten sound horizon scale at the recombination epoch by introducing extra energy components such as the extra radiation or early dark energy (EDE) is a simple approach to so-called the Hubble tension. We compare EDE models, an extra radiation model and an EDE and extra radiation co-existing model with paying attention to the fit to big bang nucleosynthesis (BBN). We find that a fit to BBN in EDE models also is somewhat poorer than that in the $Λ$CDM model, because the increased inferred baryon asymmetry leads to smaller deuterium abundance. We find that an extra radiation-EDE co-existing model indicates the largest present Hubble parameter $H_0$ between models studied. We also the examine data sets dependence, whether we include BBN or not. The difference in an extra radiation model is $3.22 < N_\mathrm{eff} < 3.49 \,(68 \%)$ for data sets without BBN and $3.16 < N_\mathrm{eff} < 3.40 \,(68 \%)$ for data sets with BBN, and is so large that the $1σ$ border of the larger side becomes the $2σ$ border.

astro-ph.CO↗

arXiv2021

Hubble tension in lepton asymmetric cosmology with an extra radiation

We study the fit of cosmological models with two additional free parameters $N_\mathrm{eff}$ and $ξ_e$ in addition to the parameters of $Λ$CDM. We introduce extra radiation components such as hot axions or sterile neutrinos in addition to the energy density of neutrinos with large neutrino degeneracy. Then, a larger $N_\mathrm{eff}$ is allowed without spoiling Big Bang Nucleosynthesis (BBN), as positive neutrino degeneracy $ξ_e$ could improve BBN fit. By analysing the data from Planck, baryon acoustic oscillation (BAO), BBN and type-Ia supernovae (SNeIa), it can be seen that the Hubble tension can be ameliorated for $ξ_{e}\simeq 0.04$ and $0.3 \lesssim ΔN_\mathrm{eff} \lesssim 0.6$.

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