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Abstract We present cosmological constraints on deviations from general relativity (GR) from the first-year of clustering observations from the Dark Energy Spectroscopic Instrument (DESI) in combination with other available datasets including the CMB data from Planck with CMB-lensing from Planck and ACT, BBN constraints on the physical baryon density, the galaxy weak lensing and clustering from DESY3 and supernova data from DESY5. We first consider the  μ(a,k)–Σ(a,k) modified gravity (MG) parameterization (as well asη(a,k)) in a ΛCDM and aw₀w_aCDM cosmological backgrounds. Using a functional form for time-only evolution givesμ₀= 0.11^+0.44_-0.54from DESI(FS+BAO)+BBN and a wide prior onn_s. Using DESI(FS+BAO)+CMB+DESY3+DESY5-SN, we obtainμ₀= 0.05 ± 0.22 and Σ₀= 0.008 ± 0.045 and similarlyμ₀= 0.02^+0.19_-0.24andη₀= 0.09^+0.36_-0.60, in an ΛCDM background. Inw₀w_aCDM we obtainμ₀= -0.24^+0.32_-0.28and Σ₀= 0.006 ± 0.043, consistent with GR, and we still find a preference of the data for a dynamical dark energy withw₀> -1 andw_a< 0. Using functional dependencies in both time and scale givesμ₀and Σ₀with a same level of precision as above but other scale MG parameters remain hard to constrain. We then move to binned parameterizations in a ΛCDM background starting with two bins in redshift and obtain,μ₁= 1.02 ± 0.13,μ₂= 1.04 ± 0.11, Σ₁= 1.021 ± 0.029 and Σ₂= 1.022^+0.027_-0.023, all consistent with the unity value of GR in the binning formalism. We then extend the analysis to combine two bins in redshift and two in scale giving 8 MG parameters that we find all consistent with GR. We note that we find here that the tension reported in previous studies about Σ₀being inconsistent with GR when using Planck PR3 data goes away when we use the recentLoLLiPoP+HiLLiPoPlikelihoods. As noted in previous studies, this seems to indicate that the tension is indeed related to the CMB lensing anomaly in PR3 which is also resolved when using the recent likelihoods. We then constrain the class of Horndeski theory in the effective field theory of dark energy approach. We consider both EFT-basis andα-basis in the analysis. Assuming a power law parameterization for the EFT function Ω, which controls non-minimal coupling, we obtain Ω₀= 0.012^+0.001_-0.012ands₀= 0.996^+0.54_-0.20from the combination of DESI(FS+BAO)+DESY5SN+CMB in a ΛCDM background, which are consistent with GR. Similar results are obtained when using theα-basis and assuming no-braiding (α_B= 0) giving  c_M< 1.14 at 95% CL in a ΛCDM background, also in agreement with GR. However, we see a mild yet consistent indication forc_B> 0 whenα_Bis allowed to vary which will require further study to determine whether this is due to systematics or new physics. 

We conduct an extended analysis of dark energy constraints, in support of the findings of the Dark Energy Spectroscopic Instrument (DESI) second data release cosmology key paper, including DESI data, Planck cosmic microwave background observations, and three different supernova compilations. Using a broad range of parametric and nonparametric methods, we explore the dark energy phenomenology and find consistent trends across all approaches, in good agreement with the $w_0{w}_a\mathrm{CDM}$(cold dark matter) key paper results. Even with the additional flexibility introduced by nonparametric approaches, such as binning and Gaussian processes, we find that extending $\mathrm{\Lambda }\mathrm{CDM}$to include a two-parameter $w\left(z\right)$is sufficient to capture the trends present in the data. Finally, we examine three dark energy classes with distinct dynamics, including quintessence scenarios satisfying $w\ge -1$, to explore what underlying physics can explain such deviations. The current data indicate a clear preference for models that feature a phantom crossing; although alternatives lacking this feature are disfavored, they cannot yet be ruled out. Our analysis confirms that the evidence for dynamical dark energy, particularly at low redshift ( $z\lesssim 0.3$), is robust and stable under different modeling choices. 

Context. In February 2017 the blazar OJ 287, one of the best super-massive binary-black-hole-system candidates, was detected for the first time at very high energies (VHEs; E  > 100 GeV) with the ground-based γ -ray observatory VERITAS. Aims. Very high energy γ rays are thought to be produced in the near vicinity of the central engine in active galactic nuclei. For this reason, and with the main goal of providing useful information for the characterization of the physical mechanisms connected with the observed teraelectronvolt flaring event, we investigate the parsec-scale source properties by means of high-resolution very long baseline interferometry observations. Methods. We use 86 GHz Global Millimeter-VLBI Array (GMVA) observations from 2015 to 2017 and combine them with additional multiwavelength radio observations at different frequencies from other monitoring programs. We investigate the source structure by modeling the brightness distribution with two-dimensional Gaussian components in the visibility plane. Results. In the GMVA epoch following the source VHE activity, we find a new jet feature (labeled K) at ∼0.2 mas from the core region and located in between two quasi-stationary components (labeled S1 and S2). Multiple periods of enhanced activity are detected at different radio frequencies before and during the VHE flaring state. Conclusions. Based on the findings of this work, we identify as a possible trigger for the VHE flaring emission during the early months of 2017 the passage of a new jet feature through a recollimation shock (represented by the model-fit component S1) in a region of the jet located at a de-projected distance of ∼10 pc from the radio core. 

Despite its importance in central nervous system development, development of the human neural tube (NT) remains poorly understood, given the challenges of studying human embryos, and the developmental divergence between humans and animal models. We report a human NT development model, in which NT-like tissues, neuroepithelial (NE) cysts, are generated in a bioengineered neurogenic environment through self-organization of human pluripotent stem cells (hPSCs). NE cysts correspond to the neural plate in the dorsal ectoderm and have a default dorsal identity. Dorsal-ventral (DV) patterning of NE cysts is achieved using retinoic acid and/or sonic hedgehog and features sequential emergence of the ventral floor plate, P3, and pMN domains in discrete, adjacent regions and a dorsal territory progressively restricted to the opposite dorsal pole. This hPSC-based, DV patterned NE cyst system will be useful for understanding the self-organizing principles that guide NT patterning and for investigations of neural development and neural disease.