arXiv subjects

Sêcloka L. Guedezounme

Publications and source records attributed to Sêcloka L. Guedezounme.

6 recordsLinked to original sources

arXiv2026

Beyond ΛCDM with the SKA Observatory -- II: Unveiling the Secrets of the Early Universe

The origins of the universe remain one of the biggest mysteries in modern cosmology. While the Planck satellite has provided a wealth of information about the early universe, there is still much to be discovered. The Square Kilometre Array Observatory (SKAO) offers a unique opportunity to probe the universe's infancy, going beyond the current limitations of our knowledge. By measuring the power spectrum of biased tracers of the dark matter distribution on the largest cosmological scales and exploring beyond 2-point statistics, SKAO will enable us to refine our understanding of the primordial universe, including the shape of the inflationary power spectrum and the presence of primordial non-Gaussianity. In this chapter we will review recent works looking at the potential of SKAO's surveys, and how synergies with other surveys can revolutionize our understanding of the origins of the cosmos.

astro-ph.CO↗

arXiv2026

Unbiased analysis of primordial non-Gaussianity: the multipoles of the full relativistic power spectrum

A major goal of ongoing and future cosmological surveys of the large-scale structure is to measure local type primordial non-Gaussianity in the galaxy power spectrum through the scale-dependent bias. General relativistic effects have been shown to be degenerate with this measurement, therefore requiring a non-Newtonian approach. In this work, we develop a consistent framework to compute integrated effects, including lensing convergence, time delay, and integrated Sachs--Wolfe, along with the local relativistic projection and wide-separation corrections in the multipoles of the power spectrum. We show that, for a \textit{Euclid}-like H$α$-line galaxy survey and a MegaMapper-like Lyman-break galaxy survey, ignoring these effects leads to a bias on the best fit measurement of the amplitude of primordial non-Gaussianity, $f_{\rm NL}$, of around $ 3\,σ$ and $ 20 \, σ$ respectively. When we include these corrections, the uncertainty in our knowledge of the luminosity function leads to further uncertainty in our measurement of $f_{\rm NL}$. In this work, we show that this degeneracy can be partly mitigated by using a bright-faint multi-tracer analysis, where the observed galaxy sample is subdivided into two separate populations based on luminosity, which provides a $15$--$20\%$ improvement on the forecasted constraints of local type $f_{\rm NL}$. In addition, we present a novel calculation of the full multi-tracer covariance with the inclusion of wide-separation corrections~-- all of these results are implemented in the \textit{Python} code \textsc{CosmoWAP}.

astro-ph.CO↗

arXiv2026

Impact of lensing magnification on the power spectrum turnover

The turnover scale $k_0$ of the matter power spectrum -- and consequently of the standard galaxy power spectrum monopole -- encodes a fundamental signature of matter-radiation equality and constitutes an important standard ruler independent of baryon acoustic oscillations. In principle, we can detect the turnover at multiple redshifts and amplify the signal by stacking redshift bins. However, in spectroscopic surveys reaching high redshifts, such as the Euclid H$α$ survey and the proposed MegaMapper Lyman-break galaxy survey, the monopole of the observed galaxy power spectrum receives a scale-dependent correction from lensing magnification. This can modify the signal shape and shift the turnover scale, undermining its use as a standard ruler. Using mock surveys similar to Euclid and MegaMapper, we forecast this shift and the consequent bias in the turnover scale that is recovered from the mock data. The shift in the turnover scale grows with redshift, leading to a maximum bias of $\sim 0.4σ$ (Euclid-like) and $\sim 3.6σ$ (MegaMapper-like). To avoid a bias $>1σ$, the maximum redshift for a MegaMapper-like survey is $z\approx 2.9$. Data in the remaining range $2.9\lesssim z\le 5$ does not directly provide a reliable recovery of the intrinsic turnover. In fact, we find that the turnover vanishes in a MegaMapper-like survey for $z\gtrsim 3.7$. Our results show that the lensing correction to the monopole should be included and carefully modelled when surveys are used to measure the cosmological turnover at high redshifts.

astro-ph.CO↗

arXiv2026

Phantom crossing or dark interaction?

Recent results from DESI BAO measurements, together with Planck CMB and Pantheon+ data, suggest that there may be a `phantom' phase ($w_{\rm de}<-1$) in the expansion of the Universe. This inference follows when the $w_0, w_a$ parametrization for the dark energy equation of state $w_{\rm de}$ is used to fit the data. Since phantom dark energy in general relativity is unphysical, we investigate the possibility that the phantom behaviour is not intrinsic, but effective -- due to a non-gravitational interaction between dark matter and non-phantom dark energy. To this end, we assume a physically motivated thawing quintessence-like form of the intrinsic dark energy equation of state $w_{\rm de}$. Then we use a $w_0, w_a$ model for the \emph{effective} equation of state of dark energy. We find that the data favours a phantom crossing for the effective dark energy, but only at low significance. The intrinsic equation of state of dark energy is non-phantom, without imposing any non-phantom priors. A nonzero interaction is favoured at more than $3σ$ at $z\sim0.3$. The energy flows from dark matter to dark energy at early times and reverses at later times.

astro-ph.CO↗

arXiv2025

Primordial non-Gaussianity -- the effects of relativistic and wide-angle corrections to the power spectrum

Wide-angle and relativistic corrections to the Newtonian and flat-sky approximations are important for accurate modeling of the galaxy power spectrum of next-generation galaxy surveys. In addition to Doppler and Sachs-Wolfe relativistic corrections, we include the effects of lensing convergence, time delay and integrated Sachs-Wolfe. We investigate the impact of these corrections on measurements of the local primordial non-Gaussianity parameter $f_{\mathrm{NL}}$, using two futuristic spectroscopic galaxy surveys, planned for SKAO2 and MegaMapper. In addition to the monopole, we include the quadrupole of the galaxy Fourier power spectrum. The quadrupole is much more sensitive to the corrections than the monopole. The combination with the quadrupole improves the precision on $f_{\mathrm{NL}}$ by $\sim {45}\%$ and $\sim {63}\%$ for SKAO2 and MegaMapper respectively. {Neglecting the wide-angle and relativistic corrections produces a shift in $f_{\mathrm{NL}}$ which is very sensitive to the magnification bias and the redshift evolution of the comoving number density. In the case of SKAO2, the shift in $f_{\mathrm{NL}}$ is negligible -- since the contributions to the shift from integrated and non-integrated effects nearly cancel. For MegaMapper, there is only partial cancellation of integrated and non-integrated effects and the shift is $\sim {0.6} \, σ$.} We point out that some of the approximations made in the wide-angle and relativistic corrections may artificially suppress the shift in $f_{\mathrm{NL}}$.

astro-ph.CO↗

arXiv2024

Relativistic and wide-angle corrections to galaxy power spectra

Galaxy surveys contain information on the largest scales via wide-angle and relativistic contributions. By combining two different galaxy populations, we can suppress the strong cosmic variance on ultra-large scales and thus enhance the detectability of the signals. The relativistic Doppler and Sachs-Wolfe effects are of a similar magnitude to the leading wide-angle corrections, so that it is important to treat them together, especially since they can partially cancel. The power spectra depend on the choice of line of sight for each galaxy pair and we present results for a general line of sight. Then we estimate the detection significance of the auto- and cross-power spectra for a variety of cases. We use two futuristic galaxy samples based on a `beyond-DESI' survey and a SKA Phase 2 survey, covering 15,000\,deg$^2$ up to $z=1$. We find a detection significance for the total relativistic wide-angle effects that ranges from $\sim 5σ$ to $>15σ$, depending on the line-of-sight configuration.

astro-ph.CO↗