Browsing by Autor "Shadab Alam"

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Atacama Cosmology Telescope DR6 and DESI: Structure growth measurements from the cross-correlation of DESI legacy imaging galaxies and CMB lensing from ACT DR6 and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>P</mml:mi><mml:mi>l</mml:mi><mml:mi>a</mml:mi><mml:mi>n</mml:mi><mml:mi>c</mml:mi><mml:mi>k</mml:mi></mml:math> PR4
(American Physical Society, 2025) Frank J. Qu; Qianjun Hang; Gerrit S. Farren; Boris Bolliet; J. Aguilar; S. P. Ahlen; Shadab Alam; D. Brooks; Yan-Chuan Cai; E. Calabrese
We measure the growth of cosmic density fluctuations on large scales and across the redshift range <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mn>0.3</a:mn><a:mo><</a:mo><a:mi>z</a:mi><a:mo><</a:mo><a:mn>0.8</a:mn></a:math> through galaxy clustering and the cross-correlation of the ACT data release 6 cosmic microwave background (CMB) lensing map and galaxies from the Dark Energy Spectroscopic Instrument Legacy Survey, using three galaxy samples spanning the redshifts of <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"><c:mn>0.3</c:mn><c:mo>≲</c:mo><c:mi>z</c:mi><c:mo>≲</c:mo><c:mn>0.45</c:mn></c:math>, <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mn>0.45</e:mn><e:mo>≲</e:mo><e:mi>z</e:mi><e:mo>≲</e:mo><e:mn>0.6</e:mn></e:math>, <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline"><g:mn>0.6</g:mn><g:mo>≲</g:mo><g:mi>z</g:mi><g:mo>≲</g:mo><g:mn>0.8</g:mn></g:math>. We adopt a scale cut where nonlinear effects are negligible, so that the cosmological constraints are derived from the linear regime. We determine the amplitude of matter fluctuations over all three redshift bins using Atacama Cosmology Telescope (ACT) data alone to be <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"><i:msub><i:mi>S</i:mi><i:mn>8</i:mn></i:msub><i:mo>≡</i:mo><i:msub><i:mi>σ</i:mi><i:mn>8</i:mn></i:msub><i:mo stretchy="false">(</i:mo><i:msub><i:mi mathvariant="normal">Ω</i:mi><i:mi>m</i:mi></i:msub><i:mo>/</i:mo><i:mn>0.3</i:mn><i:msup><i:mo stretchy="false">)</i:mo><i:mn>0.5</i:mn></i:msup><i:mo>=</i:mo><i:mn>0.772</i:mn><i:mo>±</i:mo><i:mn>0.040</i:mn></i:math> in a joint analysis combining the three redshift bins and ACT lensing alone. Using a combination of ACT and data we obtain <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:msub><n:mi>S</n:mi><n:mn>8</n:mn></n:msub><n:mo>=</n:mo><n:mn>0.765</n:mn><n:mo>±</n:mo><n:mn>0.032</n:mn></n:math>. The lowest redshift bin used is the least constraining and exhibits a <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mo>∼</p:mo><p:mn>2</p:mn><p:mi>σ</p:mi></p:math> tension with the other redshift bins; thus we also report constraints excluding the first redshift bin, giving <r:math xmlns:r="http://www.w3.org/1998/Math/MathML" display="inline"><r:msub><r:mi>S</r:mi><r:mn>8</r:mn></r:msub><r:mo>=</r:mo><r:mn>0.785</r:mn><r:mo>±</r:mo><r:mn>0.033</r:mn></r:math> for the combination of ACT and . This result is in excellent agreement at the <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline"><t:mn>0.3</t:mn><t:mi>σ</t:mi></t:math> level with measurements from galaxy lensing, but is <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline"><v:mn>1.8</v:mn><v:mi>σ</v:mi></v:math> lower than predictions based on primary CMB data. Understanding whether this hint of discrepancy in the growth of structure at low redshifts arises from a fluctuation, from systematics in data, or from new physics is a high priority for forthcoming CMB lensing and galaxy cross-correlation analyses.
DESI DR2 results. II. Measurements of baryon acoustic oscillations and cosmological constraints
(American Physical Society, 2025) M. Abdul Karim; J. Aguilar; S. P. Ahlen; Shadab Alam; L. Allen; Carlos Allende Prieto; O. Alves; Abhijeet Anand; U. Andrade; E. Armengaud
We present baryon acoustic oscillation (BAO) measurements from more than 14 million galaxies and quasars drawn from the Dark Energy Spectroscopic Instrument (DESI) Data Release 2 (DR2), based on three years of operation. For cosmology inference, these galaxy measurements are combined with DESI Lyman- <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mi>α</a:mi> </a:math> forest BAO results presented in a companion paper (M. Abdul-Karim , companion paper, .). The DR2 BAO results are consistent with DESI DR1 and the Sloan Digital Sky Survey, and their distance-redshift relationship matches those from recent compilations of supernovae (SNe) over the same redshift range. The results are well described by a flat <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi mathvariant="normal">Λ</c:mi> </c:math> cold dark matter ( <f:math xmlns:f="http://www.w3.org/1998/Math/MathML" display="inline"> <f:mi mathvariant="normal">Λ</f:mi> <f:mi>CDM</f:mi> </f:math> ) model, but the parameters preferred by BAO are in mild, <i:math xmlns:i="http://www.w3.org/1998/Math/MathML" display="inline"> <i:mn>2.3</i:mn> <i:mi>σ</i:mi> </i:math> tension with those determined from the cosmic microwave background (CMB), although the DESI results are consistent with the acoustic angular scale <k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline"> <k:msub> <k:mi>θ</k:mi> <k:mo>*</k:mo> </k:msub> </k:math> that is well measured by Planck. This tension is alleviated by dark energy with a time-evolving equation of state parametrized by <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline"> <m:msub> <m:mi>w</m:mi> <m:mn>0</m:mn> </m:msub> </m:math> and <o:math xmlns:o="http://www.w3.org/1998/Math/MathML" display="inline"> <o:msub> <o:mi>w</o:mi> <o:mi>a</o:mi> </o:msub> </o:math> , which provides a better fit to the data, with a favored solution in the quadrant with <q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline"> <q:msub> <q:mi>w</q:mi> <q:mn>0</q:mn> </q:msub> <q:mo>></q:mo> <q:mo>−</q:mo> <q:mn>1</q:mn> </q:math> and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline"> <s:msub> <s:mi>w</s:mi> <s:mi>a</s:mi> </s:msub> <s:mo><</s:mo> <s:mn>0</s:mn> </s:math> . This solution is preferred over <u:math xmlns:u="http://www.w3.org/1998/Math/MathML" display="inline"> <u:mi mathvariant="normal">Λ</u:mi> <u:mi>CDM</u:mi> </u:math> at <x:math xmlns:x="http://www.w3.org/1998/Math/MathML" display="inline"> <x:mn>3.1</x:mn> <x:mi>σ</x:mi> </x:math> for the combination of DESI BAO and CMB data. When also including SNe, the preference for a dynamical dark energy model over <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline"> <z:mi mathvariant="normal">Λ</z:mi> <z:mi>CDM</z:mi> </z:math> ranges from <cb:math xmlns:cb="http://www.w3.org/1998/Math/MathML" display="inline"> <cb:mn>2.8</cb:mn> <cb:mo>−</cb:mo> <cb:mn>4.2</cb:mn> <cb:mi>σ</cb:mi> </cb:math> depending on which SNe sample is used. We present evidence from other data combinations which also favor the same behavior at high significance. From the combination of DESI and CMB we derive 95% upper limits on the sum of neutrino masses, finding <eb:math xmlns:eb="http://www.w3.org/1998/Math/MathML" display="inline"> <eb:mo>∑</eb:mo> <eb:msub> <eb:mi>m</eb:mi> <eb:mi>ν</eb:mi> </eb:msub> <eb:mo><</eb:mo> <eb:mn>0.064</eb:mn> <eb:mtext> </eb:mtext> <eb:mtext> </eb:mtext> <eb:mi>eV</eb:mi> </eb:math> assuming <gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline"> <gb:mi mathvariant="normal">Λ</gb:mi> <gb:mi>CDM</gb:mi> </gb:math> and <jb:math xmlns:jb="http://www.w3.org/1998/Math/MathML" display="inline"> <jb:mo>∑</jb:mo> <jb:msub> <jb:mi>m</jb:mi> <jb:mi>ν</jb:mi> </jb:msub> <jb:mo><</jb:mo> <jb:mn>0.16</jb:mn> <jb:mtext> </jb:mtext> <jb:mtext> </jb:mtext> <jb:mi>eV</jb:mi> </jb:math> in the <lb:math xmlns:lb="http://www.w3.org/1998/Math/MathML" display="inline"> <lb:msub> <lb:mi>w</lb:mi> <lb:mn>0</lb:mn> </lb:msub> <lb:msub> <lb:mi>w</lb:mi> <lb:mi>a</lb:mi> </lb:msub> </lb:math> model. Unless there is an unknown systematic error associated with one or more datasets, it is clear that <nb:math xmlns:nb="http://www.w3.org/1998/Math/MathML" display="inline"> <nb:mi mathvariant="normal">Λ</nb:mi> <nb:mi>CDM</nb:mi> </nb:math> is being challenged by the combination of DESI BAO with other measurements and that dynamical dark energy offers a possible solution.