Exploring new physics in the late Universe’s expansion through non-parametric inference

Abstract

AbstractIn this study, we investigate deviations from the Planck-$$\Lambda $$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math>CDM model in the late universe ($$z \lesssim 2.5$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>2.5</mml:mn> </mml:mrow> </mml:math>) using the Gaussian Processes method, with minimal assumptions. Our goal is to understand where exploring new physics in the late universe is most relevant. We analyze recent Cosmic Chronometers (CC), Type Ia Supernovae (SN), and Baryon Acoustic Oscillations (BAO) data. By examining reconstructions of the dimensionless parameter $$\delta (z)$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>δ</mml:mi> <mml:mo>(</mml:mo> <mml:mi>z</mml:mi> <mml:mo>)</mml:mo> </mml:mrow> </mml:math>, which measures deviations of the Hubble parameter from the Planck-$$\Lambda $$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math>CDM predictions, we identify intriguing features at low ($$z \lesssim 0.5$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:math>) and high ($$z \gtrsim 2$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>≳</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math>) redshifts. Deviations from the Planck-$$\Lambda $$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math>CDM model were not significant between $$0.5\lesssim z \lesssim 2$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>0.5</mml:mn> <mml:mo>≲</mml:mo> <mml:mi>z</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math>. Using the combined CC+SN+BAO dataset, we gain insights into dark energy (DE) dynamics, resembling characteristics of omnipotent DE, extending beyond quintessence and phantom models. DE exhibits n-quintessence traits for $$z\gtrsim 2$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>≳</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math>, transitioning with a singularity around $$z\sim 2$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math> to usual phantom traits in $$1\lesssim z\lesssim 2$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>≲</mml:mo> <mml:mi>z</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math>. DE characteristics differ between scenarios ($$H_0$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>H</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math>-SH0ES and $$H_0$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>H</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math>-$$\Lambda $$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math> &amp;CMB), with $$H_0$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>H</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math>-SH0ES leaning towards phantom traits and $$H_0$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>H</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math>-$$\Lambda $$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>Λ</mml:mi> </mml:math> &amp;CMB towards quintessence. We suggest exploring new physics at $$z\lesssim 0.5$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:math> and $$1.5\lesssim z\lesssim 2.5$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1.5</mml:mn> <mml:mo>≲</mml:mo> <mml:mi>z</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>2.5</mml:mn> </mml:mrow> </mml:math>, particularly around $$z = 2$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>=</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:math>, to understand cosmological tensions such as $$H_0$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>H</mml:mi> <mml:mn>0</mml:mn> </mml:msub> </mml:math> and $$S_8$$<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>S</mml:mi> <mml:mn>8</mml:mn> </mml:msub> </mml:math>.