Dr Deaglan Bartlett: Publications

SYREN-HALOFIT: A fast, interpretable, high-precision formula for the ΛCDM nonlinear matter power spectrum

Astronomy & Astrophysics EDP Sciences 686 (2024) ARTN A150

Authors:

Deaglan J Bartlett, Benjamin D Wandelt, Matteo Zennaro, Pedro G Ferreira, Harry Desmond

Abstract:

Context.Rapid and accurate evaluation of the nonlinear matter power spectrum,P(k), as a function of cosmological parameters and redshift is of fundamental importance in cosmology. Analytic approximations provide an interpretable solution, yet current approximations are neither fast nor accurate relative to numerical emulators.Aims.We aim to accelerate symbolic approximations toP(k) by removing the requirement to perform integrals, instead using short symbolic expressions to compute all variables of interest. We also wish to make such expressions more accurate by re-optimising the parameters of these models (using a larger number of cosmologies and focussing on cosmological parameters of more interest for present-day studies) and providing correction terms.Methods.We use symbolic regression to obtain simple analytic approximations to the nonlinear scale,kσ, the effective spectral index,neff, and the curvature,C, which are required for theHALOFITmodel. We then re-optimise the coefficients ofHALOFITto fit a wide range of cosmologies and redshifts. We then again exploit symbolic regression to explore the space of analytic expressions to fit the residuals betweenP(k) and the optimised predictions ofHALOFIT. Our results are designed to match the predictions ofEUCLIDEMULATOR2, but we validate our methods againstN-body simulations.Results.We find symbolic expressions forkσ,neffandCwhich have root mean squared fractional errors of 0.8%, 0.2% and 0.3%, respectively, for redshifts below 3 and a wide range of cosmologies. We provide re-optimisedHALOFITparameters, which reduce the root mean squared fractional error (compared toEUCLIDEMULATOR2) from 3% to below 2% for wavenumbersk = 9 × 10−3 − 9 h Mpc−1. We introduceSYREN-HALOFIT(symbolic-regression-enhancedHALOFIT), an extension toHALOFITcontaining a short symbolic correction which improves this error to 1%. Our method is 2350 and 3170 times faster than currentHALOFITandHMCODEimplementations, respectively, and 2680 and 64 times faster thanEUCLIDEMULATOR2 (which requires runningCLASS) and theBACCOemulator. We obtain comparable accuracy toEUCLIDEMULATOR2 and theBACCOemulator when tested onN-body simulations.Conclusions.Our work greatly increases the speed and accuracy of symbolic approximations toP(k), making them significantly faster than their numerical counterparts without loss of accuracy.

Constraints on dark matter and astrophysics from tomographic γ-ray cross-correlations

Physical Review D: Particles, Fields, Gravitation and Cosmology American Physical Society 109 (2024) 103517

Authors:

Anya Paopiamsap, David Alonso, Deaglan Bartlett, Maciej Bilicki

Abstract:

We study the cross-correlation between maps of the unresolved 𝛾-ray background constructed from the 12-year data release of the Fermi Large-Area Telescope, and the overdensity of galaxies in the redshift range 𝑧≲0.4 as measured by the 2MASS photometric redshift survey and the WISE-SuperCOSMOS photometric survey. A signal is detected at the 8−10⁢𝜎 level, which we interpret in terms of both astrophysical 𝛾-ray sources, and weakly interacting massive particles (WIMP) dark matter decay and annihilation. The sensitivity achieved allows us to characterise the energy and redshift dependence of the signal, and we show that the latter is incompatible with a pure dark matter origin. We thus use our measurement to place an upper bound on the WIMP decay rate and the annihilation cross section, finding constraints that are competitive with those found in other analyses. Our analysis is based on the extraction of clean model-independent observables that can then be used to constrain arbitrary astrophysical and particle physics models. In this sense we produce measurements of the 𝛾-ray emissivity as a function of redshift and rest-frame energy 𝜖, and of a quantity 𝐹⁡(𝜖) encapsulating all WIMP parameters relevant for dark matter decay or annihilation. We make these measurements, together with a full account of their statistical uncertainties, publicly available.

Constraints on dark matter and astrophysics from tomographic γ -ray cross-correlations

Physical Review D (particles, fields, gravitation, and cosmology) American Physical Society 109:10 (2024) 103517

Authors:

Anya Paopiamsap, David Alonso, Deaglan J Bartlett, Maciej Bilicki

Abstract:

We study the cross-correlation between maps of the unresolved <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>γ</a:mi></a:math>-ray background constructed from the 12-year data release of the Large-Area Telescope, and the overdensity of galaxies in the redshift range <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mi>z</c:mi><c:mo>≲</c:mo><c:mn>0.4</c:mn></c:math> as measured by the 2MASS photometric redshift survey and the WISE-SuperCOSMOS photometric survey. A signal is detected at the <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>8</e:mn><e:mo>−</e:mo><e:mn>10</e:mn><e:mi>σ</e:mi></e:math> level, which we interpret in terms of both astrophysical <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mi>γ</g:mi></g:math>-ray sources, and weakly interacting massive particles (WIMP) dark matter decay and annihilation. The sensitivity achieved allows us to characterise the energy and redshift dependence of the signal, and we show that the latter is incompatible with a pure dark matter origin. We thus use our measurement to place an upper bound on the WIMP decay rate and the annihilation cross section, finding constraints that are competitive with those found in other analyses. Our analysis is based on the extraction of clean model-independent observables that can then be used to constrain arbitrary astrophysical and particle physics models. In this sense we produce measurements of the <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:mi>γ</i:mi></i:math>-ray emissivity as a function of redshift and rest-frame energy <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"><k:mi>ϵ</k:mi></k:math>, and of a quantity <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"><m:mi>F</m:mi><m:mo stretchy="false">(</m:mo><m:mi>ϵ</m:mi><m:mo stretchy="false">)</m:mo></m:math> encapsulating all WIMP parameters relevant for dark matter decay or annihilation. We make these measurements, together with a full account of their statistical uncertainties, publicly available. Published by the American Physical Society 2024

Bye-bye, Local-in-matter-density Bias: The Statistics of the Halo Field Are Poorly Determined by the Local Mass Density

ArXiv 2405.00635 (2024)

Authors:

Deaglan J Bartlett, Matthew Ho, Benjamin D Wandelt

The Inefficiency of Genetic Programming for Symbolic Regression -- Extended Version

ArXiv 2404.17292 (2024)

Authors:

Gabriel Kronberger, Fabricio Olivetti de Franca, Harry Desmond, Deaglan J Bartlett, Lukas Kammerer

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