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Eoin Ó Colgáin

Publications and source records attributed to Eoin Ó Colgáin.

At least 19 recordsLinked to original sources

Tracking High-Impact Researchers Through Highly Cited Tails

It is well recognised that field weighted citations are approximately lognormally distributed. This skewness reflects competition for attention, whereby most publications are gradually forgotten and only a minority continue to be recalled years later. Exploiting this observation, we construct a researcher-level indicator based on authorship of top 10% cited papers in All Science Journal Code (ASJC) bins and apply it to publications affiliated with Irish institutions over a typical funding cycle. Restricting attention largely to original research papers, we find that researchers authoring strictly more than one ASJC top-decile paper in a given year exhibit persistent participation in the highly cited tail of the literature in subsequent years, thus the simple track record indicator possesses predictive value. In contrast, the median researcher in cohorts of Research Ireland and European Research Council awardees selected through qualitative peer review either authors no top-decile paper or less than the median researcher in our ranking. These results demonstrate that research excellence as judged by qualitative peer review and influence on the research literature identify substantially different cohorts of researchers. In the absence of evidence, funding bodies and universities may conflate these two. While research reputation may be enhanced through many channels, highly cited papers constitute the most widely observable manifestation of international scholarly influence. Our analysis indicates that literature influence may be improved through greater use of data in track record pre-screening prior to qualitative peer review.

physics.soc-ph↗

A Prediction for DESI Full-Shape: Increasing Tomographic $Ω_m(z)$ Trend

To confirm $Λ$CDM deviations are due to missing physics (not systematics), one should demonstrate that the model fitting parameters exhibit qualitatively similar redshift drift across independent observables. This is the only way one guarantees new physics. Here, we show that a recent Dark Energy Spectroscopic Instrument (DESI) DR2 Full-Shape (FS) modelling Lyman-$α$ constraint at $z_{\rm eff} = 2.33$ combined with earlier DR1 FS modelling constraints with $0.295 \leq z_{\rm eff} \leq 1.491$ leads to a straight line $Ω_m(z) = m z + c$ with slope $m = 0.022 \pm 0.012$, $1.8 σ$ removed from constant $Ω_m$. Akaike Information Criterion and Bayesian evidence confirm that constant $Ω_m$ and increasing $Ω_m(z)$ are statistically indistinguishable. Through the $Om(z)$ diagnostic, we review how increasing and decreasing $Ω_m(z)$ trends map to phantom and quintessence dark energy (DE) regimes, respectively. While FS modelling constraints map to phantom DE, the decreasing and increasing $Ω_m(z)$ trends in DESI BAO and DESI with external data make a phantom crossing inevitable. Since dynamical DE is but one interpretation for $Ω_m(z)$ trends, it is imperative that different datasets converge on their $Ω_m(z)$ trends before one jumps to physical conclusions. We forecast how DESI FS modelling $Ω_m$ constraints will improve up to the final data release and explore the implications for model selection.

astro-ph.CO↗

Crosschecking Cosmic Distances from DESI BAO and DES SNe

We perform a consistency check of DESI DR2 BAO constraints ($D_M/r_d, D_H/r_d)$ by reconstructing the same quantities from DES supernovae (SNe) in bins with the same effective redshift $z_{\textrm{eff}} \in \{ 0.510, 0.706, 0.934 \}$ and a Planck $r_d$ prior. Through mock analysis we show that $D_M(z_{\rm eff})$ and $D_{H}(z_{\rm eff})$ can be locally reconstructed model agnostically from $Λ$CDM and extended models, but only if one employs frequentist methods; purely Bayesian reconstructions from Markov Chain Monte Carlo (MCMC) exhibit bias. We find that the ratio of the three $D_M/r_d$ values at different $z_{\textrm{eff}}$ are consistent with a horizontal, thus confirming that the distance duality relation holds up to calibration. However, the $D_H/r_d$ ratio shows a decreasing trend driven by the $z_{\textrm{eff}} = 0.934$ bin, the significance of which varies from $2.5 σ$ with Bayesian methods down to $1.4 σ$ with frequentist methods. We show that replacing DES with DES-Dovekie SNe reduces the significance to $1.7 σ$ and $1.2 σ$ in Bayesian and frequentist approaches, respectively. We conclude that distances reconstructed from SNe show good agreement with DESI BAO distances across the redshifts studied. We also note that $D_M(z_{\rm eff} = 0.510)/r_d$ reconstructed from SNe favours DESI BAO over transversal BAO against a backdrop of a $3.7 σ$ disagreement.

astro-ph.CO↗

How much has DESI dark energy evolved since DR1?

DESI has reported a dynamical dark energy (DE) signal based on the $w_0 w_a$CDM model that is in conflict with Hubble tension. Recalling that the combination of DESI DR1 BAO and DR1 full-shape (FS) modeling are consistent with $Λ$CDM, in this letter we comment on the status of fluctuations in DR1 BAO documented in \cite{DESI:2024mwx, Colgain:2024xqj} in the DR2 update. In particular, we note that neither DR1 BAO nor DR2 BAO nor DR2 BAO+CMB confronted to the $w_0 w_a$CDM model with relaxed model parameter priors confirm late-time accelerated expansion today. Translating DESI BAO constraints into flat $Λ$CDM constraints, we observe that the LRG1 constraint remains the most prominent outlier, a distinction now held jointly with ELG1, LRG2 switches from smaller to larger $Ω_m$ values relative to Planck-$Λ$CDM, and ELG data drive the relatively low $Ω_m$ in the full DR2 BAO. We observe that one cannot restore $w_0 = -1$ within one $1 σ$ by removing either LRG1 or ELG1 or LRG2, but LRG2 in DR2, in contrast to LRG1 in DR1, now has the greatest bearing on $w_0 > -1$. We conclude that BAO has yet to stabilise, but the general trend is towards greater consistency with DESI DR1 FS modeling results, where there may be no dynamical DE signal in DESI data alone.

astro-ph.CO↗

An FWCI decomposition of Science Foundation Ireland funding

In response to the 2008 global financial crisis, Science Foundation Ireland (SFI), now Research Ireland, pivoted to research with potential socioeconomic impact. Given that the latter can encompass higher technology readiness levels, which typically correlates with lower academic impact, it is interesting to understand how academic impact holds up in SFI funded research. Here we decompose SFI \textit{Investigator Awards} - arguably the most academic funding call - into $3,243$ constituent publications and field weighted citation impact (FWCI) values searchable in the SCOPUS database. Given that citation counts are skewed, we highlight the limitation of FWCI as a paper metric, which naively restricts one to comparisons of average FWCI ($\overline{\mathrm{FWCI}}$) in large samples. Neglecting publications with $\textrm{FWCI} < 0.1$ ($8.8\%$), SFI funded publications are well approximated by a lognormal distribution with $μ= -0.0761^{+0.017}_{-0.0039}$ and $ σ= 0.933^{+0.011}_{-0.012}$ at $95 \%$ confidence level. This equates to an $\overline{\mathrm{FWCI}} = 1.433^{+0.029}_{-0.015}$ well above $\overline{\mathrm{FWCI}}=1$ internationally. Broken down by award, we correct $\overline{\mathrm{FWCI}}$ for small samples using simulations and find $\sim 67\%$ exceed \textit{median} international academic interest, thus exhibiting a positive correlation between the potential for socioeconomic impact and academic interest.

cs.DL↗

On frequentist confidence intervals in a non-Gaussian regime

We study frequentist confidence intervals based on graphical profile likelihoods (Wilks' theorem, likelihood integration), and the Feldman-Cousins (FC) prescription, a generalisation of the Neyman belt construction, in a setting with non-Gaussian Markov chain Monte Carlo (MCMC) posteriors. Our simplified setting allows us to recycle the MCMC chain as an input in all methods, including mock simulations underlying the FC approach. We find all methods agree to within $10 \%$ in the close to Gaussian regime, but extending methods beyond their regime of validity leads to greater discrepancies. Importantly, we recover a $\sim 2 σ$ shift in cosmological parameters between low and high redshift cosmic chronometer data with the FC method, but only when one fits all parameters back to the mocks. We observe that fixing parameters, a common approach in the literature, risks underestimating confidence intervals.

astro-ph.CO↗

On the Analysis Dependence of DESI Dynamical Dark Energy

We continue scientific scrutiny of the DESI dynamical dark energy (DE) claim by explicitly demonstrating that the result depends on the analysis pipeline. Concretely, we define a likelihood that converts the $w_0 w_a$CDM model back into the (flat) $Λ$CDM model, which we fit to DESI constraints on the $Λ$CDM model from DR1 Full-Shape (FS) modelling and BAO. We further incorporate CMB constraints. Throughout, we find that $w_0$ and $w_a$ are within $1 σ$ of the $Λ$CDM model. Our work makes it explicit that, in contrast to DR1 and DR2 BAO, there is no dynamical DE signal in FS modelling, even when combined with BAO and CMB. Moreover, one confirms late-time accelerated expansion today $(q_0 < 0)$ at $ \gtrsim 3.4 σ$ in FS modelling + BAO. On the contrary, DR1 and DR2 BAO fail to confirm $q_0 < 0$ under similar assumptions. Our analysis highlights the fact that trustable scientific results should be independent of the analysis pipeline.

astro-ph.CO↗

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics

The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance model is constructed by a universal cosmological constant and supported by a matter sector described by the standard model of particle physics and a cold dark matter contribution, as well as very early-time inflationary physics, and underpinned by gravitation through general relativity. There have always been open questions about the soundness of the foundations of the standard model. However, recent years have shown that there may also be questions from the observational sector with the emergence of differences between certain cosmological probes. In this White Paper, we identify the key objectives that need to be addressed over the coming decade together with the core science projects that aim to meet these challenges. These discordances primarily rest on the divergence in the measurement of core cosmological parameters with varying levels of statistical confidence. These possible statistical tensions may be partially accounted for by systematics in various measurements or cosmological probes but there is also a growing indication of potential new physics beyond the standard model. After reviewing the principal probes used in the measurement of cosmological parameters, as well as potential systematics, we discuss the most promising array of potential new physics that may be observable in upcoming surveys. We also discuss the growing set of novel data analysis approaches that go beyond traditional methods to test physical models. [Abridged]

astro-ph.CO↗

Does DESI 2024 Confirm $Λ$CDM?

We demonstrate that a $\sim 2 σ$ discrepancy with the Planck-$Λ$CDM cosmology in DESI Luminous Red Galaxy (LRG) data in the redshift range $0.4 < z < 0.6$ with effective redshift $z_{\textrm{eff}} = 0.51$ translates into an unexpectedly large $Ω_m$ value, $Ω_m = 0.67^{+0.18}_{-0.17}$. We independently confirm that this anomaly drives the preference for $w_0 > -1$ in DESI data \textit{alone} confronted to the $w_0 w_a$CDM model. Given that LRG data at $z_{\textrm{eff}} = 0.51$ is at odds with Type Ia supernovae in overlapping redshifts, we expect that this anomaly will decrease in statistical significance with future DESI data releases leaving an increasing $Ω_m$ trend with effective redshift at higher redshifts. We estimate the current significance of the latter in DESI data at $\sim 1.8 σ$ and comment on how it dovetails with independent observations. It is imperative to understand what makes DESI LRG data at $z_{\textrm{eff}} = 0.51$ an outlier when it comes to $Ω_m$ determinations.

astro-ph.CO↗

Do high redshift QSOs and GRBs corroborate JWST?

The James Webb Space Telescope (JWST) is reporting massive high redshift galaxies that appear challenging from the $Λ$CDM perspective. Interpreted as a cosmological problem, this necessitates the Planck collaboration underestimating either matter density $Ω_m$ or physical matter density $Ω_m h^2$ at higher redshifts. Through standard frequentist profile likelihoods, we identify corroborating quasar (QSO) and gamma-ray burst (GRB) data sets where $Ω_m$ increases with effective redshift $z_{\textrm{eff}}$ and remains anomalously large at higher redshifts. We relax the traditional priors by allowing for $Ω_m > 1$, consistent with negative dark energy density, to locate profile likelihood peaks where possible. While the variation of $Ω_m$ with $z_{\textrm{eff}}$ is at odds with the $Λ$CDM model, demarcating frequentist confidence intervals through differences in $χ^2$ in profile likelihoods, the prevailing technique in the literature, points to $3.9 σ$ and $7.9 σ$ tensions between GRBs and QSOs, respectively, and Planck-$Λ$CDM. We explain the approximations inherent in the existing profile likelihood literature, and highlight fresh methodology that generalises the prescription. We show that alternative methods, including Bayesian approaches, lead to similar tensions. Finally, in the large sample limit, we show that Feldman-Cousins prescription for frequentist confidence intervals in the presence of a boundary (prior) leads to confidence intervals that are bounded above by Wilks' theorem.

astro-ph.CO↗

Implications of DES 5YR SNe Dataset for $Λ$CDM

Dark Energy Survey five-year supernovae data (DES 5YR SNe) in conjunction with Planck CMB and Dark Energy Spectroscopic Instrument (DESI) BAO data has detected a strong dynamical dark energy (DE) deviation from the $Λ$CDM model.Here we shift the focus of DES data to the pressureless matter sector in the $Λ$CDM model by studying the matter density parameter $Ω_m$. Employing primarily frequentist profile likelihoods, supported by complementary Bayesian methods, we demonstrate that $Ω_m$ increases with effective redshift in the DES data up to a point that there is a $2.5 σ$ discrepancy with Planck. We relax the traditional $Ω_m \leq 1$ prior to demonstrate negative DE densities $Ω_m > 1$ at the highest effective redshift probed. Nevertheless, the largest discrepancy with Planck occurs for profile likelihoods and posteriors peaked at $Ω_m < 1$ in the traditional $Λ$CDM regime. Our findings corroborate earlier observations in Pantheon and Pantheon+ datasets with an independent SNe dataset with a higher effective redshift. In an appendix, we confirm that curvature $Ω_k$ decreases with effective redshift disfavouring a flat Universe in higher redshift DES SNe at $> 3 σ$. Our choice of $Ω_k$ prior leads to an underestimation of the tension with a flat Universe.

astro-ph.CO↗

DESI and SNe: Dynamical Dark Energy, $Ω_m$ Tension or Systematics?

Dark Energy Spectroscopic Instrument (DESI) observations, when combined with Cosmic Microwave Background (CMB) and Type Ia supernovae (SNe), have led to statistically significant dynamical dark energy (DDE) claims. In this letter we reconstruct the $Λ$CDM parameter $Ω_m$ from the $w_0 w_a$CDM cosmologies advocated by the DESI collaboration. We identify i) a mild increasing $Ω_m$ trend at high redshift and ii) a sharp departure from $Λ$CDM at low redshift. The latter, which is statistically significant, is driven by SNe that are $1.9 σ- 2.5 σ$ discrepant with DESI full-shape galaxy clustering in overlapping redshift ranges. We identify a low redshift subsample of the Dark Energy Survey (DES) SNe sample that is discrepant with DESI at $3.4 σ$ despite both observables probing the same effective redshift. SNe and BAO/full-shape modeling should not disagree on $Ω_m$ at the same effective redshift. This ``$Ω_m$ tension'' most likely points to unexplored systematics. In general, any \textit{bona fide} DDE signal should be confirmed independently across observables, so the DDE claims are premature.

astro-ph.CO↗

A comparison of Bayesian and frequentist confidence intervals in the presence of a late Universe degeneracy

Hubble tension is a problem in one-dimensional (1D) posteriors, since local $H_0$ determinations are only sensitive to a single parameter. Projected 1D posteriors for $Λ$CDM cosmological parameters become more non-Gaussian with increasing effective redshift when the model is fitted to redshift-binned data in the late Universe. We explain mathematically why this non-Gaussianity arises and show using observational Hubble data (OHD) that Markov Chain Monte Carlo (MCMC) marginalisation leads to 1D posteriors that fail to track the $χ^2$ minimum at $68\%$ confidence level in high redshift bins. To gain a second perspective, we resort to profile likelihoods as a complementary technique. Doing so, we observe that $z \gtrsim 1$ cosmic chronometer (CC) data currently prefers a non-evolving (constant) Hubble parameter over a Planck-$Λ$CDM cosmology at $\sim 2 σ$. Within the Hubble tension debate, it is imperative that subsamples of data sets with differing redshifts yield similar $H_0$ values. In addition, we confirm that MCMC degeneracies observed in 2D posteriors are not due to curves of constant $χ^2$. Finally, on the assumption that the Planck-$Λ$CDM cosmological model is correct, using profile likelihoods we confirm a $>2 σ$ discrepancy with Planck-$Λ$CDM in a combination of CC and baryon acoustic oscillations (BAO) data beyond $ z \sim 1.5$. This confirms a discrepancy reported earlier with fresh methodology.

astro-ph.CO↗

Further support for $S_8$ increasing with effective redshift

In Adil et al. 2023, we reported an increasing trend in $S_8$ with effective redshift $z_{\textrm{eff}}$ based on $f σ_8(z)$ constraints over the redshift range $0 \lesssim z \lesssim 2$, and predicted that this trend would be observable in independent datasets. Recently, the studies by Artis et al. and the ACT+DESI collaboration appeared, presenting data that aligns with the expected trends. In this letter, we quantify the statistical significance of the increasing $S_8$ trends in recent studies by fitting a linear model to estimate the slope $Δ\,S_8/Δ\, z_{\textrm{eff}}$, and comparing the results to mock simulations. We find probabilities of $p = 0.0163$ and $p = 0.01893$, corresponding to approximately $2.1σ$ for each dataset. Using Fisher's method to combine the independent probabilities, we obtained $p=0.0027$ ($2.8 σ$). When we incorporate our earlier findings, the combined statistical significance reaches between $3σ$ and $3.7σ$. Finally, we discuss how ``scatter" in $σ_8$/$S_8$ constraints from recent DESI full-shape galaxy clustering fits this picture at low statistical significance. This letter continues a series of studies initiated in 2020 that explore redshift-dependent $Λ$CDM parameters as an indication of a breakdown in the standard cosmological model.

astro-ph.CO↗

$Λ$CDM Tensions: Localising Missing Physics through Consistency Checks

$Λ$CDM tensions are by definition model dependent; one sees anomalies through the prism of $Λ$CDM. Thus, progress towards tension resolution necessitates checking the consistency of the $Λ$CDM model to localise missing physics either in redshift or scale. Since the Universe is dynamical and redshift is a proxy for time, it is imperative to first perform consistency checks involving redshift, then consistency checks involving scale, as the next steps to settle the ``systematics versus new physics" debate and foster informed model building. We present a review of the hierarchy of assumptions underlying the $Λ$CDM cosmological model and comment on whether relaxing them can address the tensions. We focus on the lowest lying fruit of identifying missing physics through the identification of redshift dependent $Λ$CDM model fitting parameters. We highlight recent progress made on ${S_8:= σ_8 \sqrt{Ω_{\rm m}/0.3}}$ tension and elucidate how similar progress can be made on $H_0$ tension. Our discussions indicate that $H_0$ tension, equivalently a redshift dependent $H_0$, and a redshift dependent $S_8$ imply a problem with background $Λ$CDM cosmology.

astro-ph.CO↗

On Redshift Evolution & Negative Dark Energy Density in Pantheon+ Supernovae

Within the Friedmann-Lemaître-Robertson-Walker (FLRW) framework, the Hubble constant $H_0$ is an integration constant. Thus, consistency of the model demands observational constancy of $H_0$. We demonstrate redshift evolution of best fit $Λ$CDM parameters $(H_0, Ω_{m})$ in Pantheon+ supernove (SNe). Redshift evolution of best fit cosmological parameters is a prerequisite to finding a statistically significant evolution as well as identifying alternative models that are competitive with $Λ$CDM in a Bayesian model comparison. To assess statistical significance, we employ three different methods: i) Bayesian model comparison, ii) mock simulations and iii) profile distributions. The first shows a marginal preference for the vanilla $Λ$CDM model over an ad hoc model with 3 additional parameters and an unphysical jump in cosmological parameters at $z=1$. From mock simulations, we estimate the statistical significance of redshift evolution of best fit parameters and negative dark energy density ($Ω_m > 1$) to be in the $1-2 σ$ range, depending on the criteria employed. Importantly, in direct comparison to the same analysis with the earlier Pantheon sample we find that statistical significance of redshift evolution of best fit parameters has increased, as expected for a physical effect. Our profile distribution analysis demonstrates a shift in $(H_0, Ω_m)$ in excess of $95\%$ confidence level for SNe with redshifts $z > 1$ and also shows that a degeneracy in MCMC posteriors is not equivalent to a curve of constant $χ^2$. Our findings can be interpreted as a statistical fluctuation or unexplored systematics in Pantheon+ or $Λ$CDM model breakdown. The first two possibilities are disfavoured by similar trends in independent probes.

astro-ph.CO↗

Putting Flat $Λ$CDM In The (Redshift) Bin

Flat $Λ$CDM cosmology is specified by two constant fitting parameters at the background level in the late Universe, the Hubble constant $H_0$ and matter density (today) $Ω_m$. Mathematically, $H_0$ and $Ω_m$ are either integration constants arising from solving ordinary differential equations or are directly related to integration constants. Seen in this context, if fits of the $Λ$CDM model to cosmological probes at different redshifts lead to different $(H_0, Ω_m)$ parameters, this is a mismatch between mathematics and observation. Here, in mock observational Hubble data (OHD) (geometric probes of expansion history) we demonstrate evolution in distributions of best fit parameters with effective redshift. As a result, considerably different $(H_0, Ω_m)$ best fits from Planck-$Λ$CDM cannot be precluded in high redshift bins. We explore if OHD, Type Ia supernovae and standardisable quasar samples exhibit redshift evolution of best fit $Λ$CDM parameters. In all samples, we confirm a decreasing $H_0$ and increasing $Ω_m$ trend with increasing bin redshift. Through comparison with mocks, we confirm that similar behaviour can arise randomly within the flat $Λ$CDM model with probabilities as low as $p = 0.0021$ ($3.1 \, σ$). We present complementary profile distribution analysis confirming the shifts in cosmological parameters in high redshift bins. In particular, we identify a redshift range where Planck $(H_0, Ω_m)$ values are disfavoured at $99.6 \%$ ($2.9 σ$) confidence level in a combination of OHD and supernovae data.

astro-ph.CO↗

$S_8$ increases with effective redshift in $Λ$CDM cosmology

Hubble constant $H_0$ and weighted amplitude of matter fluctuations $S_8$ determinations are biased to higher and lower values, respectively, in the late Universe with respect to early Universe values inferred by the Planck collaboration within flat $Λ$CDM cosmology. If these anomalies are physical, i.e. not due to systematics, they naively suggest that $H_0$ decreases and $S_8$ increases with effective redshift. Here, subjecting matter density today $Ω_{m}$ to a prior, corresponding to a combination of Planck CMB and BAO data, we perform a consistency test of the Planck-$Λ$CDM cosmology and show that $S_8$ determinations from $f σ_8(z)$ constraints increase with effective redshift. Due to the redshift evolution, a $\sim 3 σ$ tension in the $S_8$ parameter with Planck at lower redshifts remarkably becomes consistent with Planck within $1 σ$ at high redshifts. This provides corroborating support for an $S_8$ discrepancy that is physical in origin. We further confirm that the flat $Λ$CDM model is preferred over a theoretically ad hoc model with a jump in $S_8$ at a given redshift. In the absence of the CMB+BAO $Ω_m$ prior, we find that $> 3 σ$ tensions with Planck in low redshift data are ameliorated by shifts in the parameters in high redshift data. Results here and elsewhere suggest that the $Λ$CDM cosmological parameters are redshift dependent. Fitting parameters that evolve with redshift is a recognisable hallmark of model breakdown.

astro-ph.CO↗