arXiv subjects

Ze-Yu Peng

Publications and source records attributed to Ze-Yu Peng.

9 recordsLinked to original sources

arXiv2026

Inverse-k Primordial Oscillations from a Symbolic Regression Search

Oscillatory features in the primordial power spectrum, potential signatures of new physics in the early universe, are usually searched for using fixed templates. In this work, we perform a template-free search for primordial features using symbolic regression. We find that both Planck and the combined Planck+ACT+SPT-3G datasets independently select an inverse-$k$ oscillation, $\cos(B/k)$ with $B\simeq4\,\mathrm{Mpc}^{-1}$, as the leading low-complexity feature. Comparing this inverse-$k$ template with standard linear and logarithmic oscillating templates, we find that it fits the data best, showing a weak preference for a non-zero amplitude. Our results show that symbolic regression as a powerful machine learning technique can provide an interpretable, model-independent approach to cosmological discovery.

astro-ph.CO↗

arXiv2026

Single field slow-roll inflation with step uplift to $n_s=1$

The early dark energy resolution of Hubble tension seems to be suggesting a scale-invariant Harrison-Zeldovich spectrum of primordial scalar perturbation, i.e. $n_s=1$ ($|n_s-1|\sim {\cal O}(0.001)$) for $H_0\sim 73$km/s/Mpc. In this work, we propose a possibility to acquire $n_s=1$ in single field slow-roll models of inflation. In our consideration, the potential of inflaton during inflation still preserve the shape of well-known single field inflation models in deep slow-roll region, but inflation ends suddenly due to a large step of inflaton potential. In particular, we investigate the implication of our scheme for chaotic inflation and Starobinski inflation, and show how they can be compatible with the observation for $n_s=1$.

astro-ph.CO↗

arXiv2026

DeepInflation: an AI agent for research and model discovery of inflation

We present DeepInflation, an AI agent designed for research and model discovery in inflationary cosmology. Built upon a multi-agent architecture, DeepInflation integrates Large Language Models (LLMs) with a symbolic regression (SR) engine and a retrieval-augmented generation (RAG) knowledge base. This framework enables the agent to automatically explore and verify the vast landscape of inflationary potentials while grounding its outputs in established theoretical literature. We demonstrate that DeepInflation can successfully discover simple and viable single-field slow-roll inflationary potentials consistent with the latest observations (with the ACT DR6 results taken as an example) or any given $n_s$ and $r$, and provide accurate theoretical context for obscure inflationary scenarios. DeepInflation serves as a prototype for a new generation of autonomous scientific discovery engines in cosmology, which enables researchers and non-experts alike to explore the inflationary landscape using natural language. This agent is available at https://github.com/pengzy-cosmo/DeepInflation.

astro-ph.CO↗

arXiv2025

Testing $n_s=1$ in light of the latest ACT and SPT data

It is commonly recognized that the primordial scalar spectral index $n_s$ is approximately $0.96-0.975$, depending on the dataset. However, this view is being completely altered by the early dark energy (EDE) resolutions of the Hubble tension, known as the most prominent tension the standard $\Lambda$CDM model is suffering from. In corresponding models with pre-recombination EDE, resolving the Hubble tension (i.e., achieving $H_0\sim 73$km/s/Mpc) must be accompanied by a shift of $n_s$ towards unity to maintain consistency with the cosmological data, which thus implies a scale invariant Harrison-Zel'dovich spectrum with $n_s=1$ $(|n_s-1|\simeq {\cal O}(0.001))$. In this work, we strengthen and reconfirm this result with the latest ground-based CMB data from ACT DR6 and SPT-3G D1, the precise measurements at high multipoles beyond the Planck angular resolution and sensitivity. Our work again highlights the importance of re-examining our understanding on the very early Universe within the broader context of cosmological tensions.

astro-ph.CO↗

arXiv2025

Tightening constraints on primordial oscillations with latest ACT and SPT data

The oscillation feature in primordial power spectrum (PPS), a fingerprint of not only a wide class of models of inflation but new physics, is of significant theoretical interest, and can be imprinted on the cosmic microwave background (CMB). In this work, we present constraints on periodic oscillations in the PPS using the latest ACT DR6 and SPT-3G D1 CMB data with the precise measurements at high multipoles beyond the Planck angular resolution and sensitivity. It is found that the combination of SPT and ACT with Planck CMB dataset significantly tightens the upper bound to $A_\mathrm{log,lin}\lesssim 0.029$ at $95\%$ C.L., showing no hint for primordial oscillations, where $A_\mathrm{log,lin}$ are the amplitudes of logarithmic and linear oscillation in the PPS, respectively. Our work presents state-of-the-art CMB constraints on primordial oscillations, highlighting the power of the ground-based CMB experiments in constraining physics beyond the simplest slow-roll models.

astro-ph.CO↗

arXiv2025

Hint of $r\simeq 0.01$ after DESI DR2 ?

In the report by BICEP/Keck collaborations, the tensor-to-scalar ratio is $r_{0.05}<0.036$ (95\% C.L.). However, recent datasets have preferred the evolving dark energy, which thus have significantly shifted the bestfit values of standard $\Lambda$CDM cosmological parameters. In this paper, we perform the joint analysis of BICEP/Keck cosmic microwave background (CMB) B-mode data, latest DESI DR2 baryon acoustic oscillations and supernova data, combined with Planck PR3 and PR4 CMB data respectively, and find $r_{0.05}=0.0159^{+0.0057}_{-0.014}$ and $r_{0.05}=0.0164^{+0.0063}_{-0.014}$. The constraints on $r$ are further tightened compared to the result of BICEP/Keck collaborations. Though there might be still systematic uncertainties in B-mode measurements due to the foreground contamination, our work is to not say what the value of $r$ is, but present the state-of-the-art constraints on $r$ and emphasize that the detection for $r$ depends potentially on our insight into the dark universe, highlighting the important role of cosmological surveys in comprehending our very early universe.

astro-ph.CO↗

arXiv2025

Dark energy and lensing anomaly in Planck CMB data

In this paper, we investigate the impact of the lensing anomaly in Planck cosmic microwave background (CMB) data on the nature of dark energy (DE). We constrain the state equation ($w_0,w_a$) of DE with the lensing scaling parameter $A_L=1$ and varying $A_L$, using the Planck PR3 and two updated Planck PR4 likelihoods, CamSpec and HiLLiPoP respectively, combined with DESI baryon acoustic oscillation (BAO) and Pantheon+ supernova data. As expected, when $A_L$ is allowed to vary, the evolving DE is not preferred due to the degeneracy between $w_0,w_a$ and $A_L$. In particular, we also consider replacing DESI BAO data with pre-DESI BAO in our analysis, and observe that DESI BAO appears to exacerbate the lensing anomaly, which is caused by the smaller matter density $\Omega_m$ it prefers, however, this effect can be offset by the shifts in $w_0$ and $w_a$ preferring the evolving DE. Our work indicates that the lensing anomaly in Planck data is worth carefully reconsidering when new cosmological survey data is combined with CMB.

astro-ph.CO↗

arXiv2024

Can recent DESI BAO measurements accommodate a negative cosmological constant?

Anti-de Sitter vacuum, which correspond to a negative cosmological constant (CC), is theoretically important and well-motivated. However, whether it exists in reality or not has always been a controversial issue. In this paper, we perform the search for the negative CC using recent Dark Energy Spectroscopic Instrument (DESI) baryon acoustic oscillation measurements combined with Planck cosmic microwave background and Pantheon Plus supernova data. Though we did not find the evidence for negative CC, we observed the indication for it, the negative CC is preferred at $>68\%$ significance level, while such a negative CC can make the state equation of evolving dark energy component (coexisting with negative CC) $w\geqslant -1$. Our work highlights the potential of upcoming cosmological surveys to search for the negative CC.

astro-ph.CO↗

arXiv2023

Testing the $n_s-H_0$ scaling relation with Planck-independent CMB data

In early dark energy (EDE) resolution of Hubble tension, the spectral index $n_s$ of primordial scalar perturbation follows a scaling relation ${\delta n_s}\simeq 0.4\frac{\delta H_0}{H_0}$, where $H_0$ is the Hubble constant. However, this $n_s-H_0$ relation was obtained based on the datasets including Planck cosmic microwave background (CMB) data. In this paper, we investigate this scaling relation with Planck-independent CMB data, i.e. ACT and SPT-3G combined with WMAP(+BAO+Pantheon), respectively. Our results show that the WMAP+SPT-3G dataset also follows this scaling relation, while the WMAP+ACT dataset seems to favor smaller $n_s$, which is related to the fact that the critical redshift $z_c$, at which EDE is excited, favored by the WMAP+ACT dataset is lower and closer to the recombination time.

astro-ph.CO↗