arXiv subjects

Matthew C. Johnson

Publications and source records attributed to Matthew C. Johnson.

At least 19 recordsLinked to original sources

arXiv2026

Dark Energy Bubble as Dynamical Dark Energy: Properties and CMB Constraints

Recent DESI results are in tension with the constant dark energy density predicted by the $\Lambda$CDM model. If dark energy is associated with the vacuum energy of a scalar field in a metastable state, it will undergo a first-order phase transition through the nucleation of bubbles containing a reduced dark energy density. In this paper, we explore the consequences of this model, where dark energy density varies in both space and time. We model a single bubble spacetime using the Israel junction conditions and derive each of the usual distance measures in this inhomogeneous cosmology. We find that the model predictions of Alcock-Paczynski distortion have features that align strikingly well with the DESI measurements if the dark energy phase transition occurred at roughly a redshift of 1.4 and if the bubble of lower dark energy density has roughly 10$\%$ less dark energy density than the outer cosmology. Despite this feature, we find that the dark energy bubble is heavily constrained by the CMB which excludes the region of parameter space that reproduces the DESI BAO measurements. Still, the peculiar features in the distance measurements of the dark energy bubble cosmology serve as a useful toy model to motivate and inform future work in the currently poorly explored area of spatially varying dynamical dark energy.

astro-ph.CO↗

arXiv2026

Constraints on the remote quadrupole field from the polarized Sunyaev Zel'dovich effect

The polarized Sunyaev Zel'dovich (pSZ) effect is a cosmic microwave background (CMB) polarization anisotropy induced by Thomson scattering from free-electrons in non-linear structure. The pSZ signal is determined by the distribution of ionized gas tracing the cosmic web and the CMB quadrupole at the location of free-electrons - the remote quadrupole field. Measuring the pSZ effect provides a consistency check of the optical depth to reionization and sheds light on the anomalous nature of the large-scale CMB temperature anisotropies, such as the low observed CMB temperature quadrupole. In this paper, we demonstrate that a CMB-CMB-galaxy bispectrum summarizes several existing pSZ statistics, and that in our observable Universe the ideal galaxy sample to detect pSZ is at $z \sim 1-2$. We evaluate the bispectrum using CMB data from Planck and ACT with galaxy density from the unWISE galaxy redshift catalog as well as Planck cosmic infrared background (CIB) maps. We do not make a statistically significant detection of the pSZ effect, which is consistent with the expected O$(1)$ signal-to-noise from this data combination. The measured amplitude of the pSZ bispectrum provides constraints on the optical depth bias associated with large-scale structure (the amplitude of the pSZ signal) of $b_q=1.02 \pm 2.64$, the optical depth to reionization of $\tau_{\rm rei} = -0.01 \pm 0.14$, and the tensor-to-scalar ratio $r$ of $\sigma_r \sim 150$ ($n_t = 0$) or $\sigma_r \sim 3$ ($n_t = -1$). We forecast that future measurements could tighten the constraints on these quantities by roughly a factor of 3, which is sufficient to provide independent confirmation of the low CMB quadrupole and the optical depth to reionization.

astro-ph.CO↗

arXiv2026

Evidence for renormalized instantons in real-time simulations of vacuum decay

While vacuum decay is traditionally described by Euclidean instanton methods, lattice simulations enable real-time modeling of dynamical observables relevant to cosmology and upcoming cold-atom analog experiments. We investigate the relationship between these approaches by extracting ensemble-averaged bubble profiles from zero-temperature simulations of a relativistic scalar field. Our observed profiles differ markedly from the bare Coleman bounce and classical thermal predictions. However, we find that instanton solutions in an appropriately renormalized potential reproduce both the measured profiles and their dependence on the UV cutoff, and predict decay rates consistent with simulations across the parameter range considered. The fact that a single renormalized Euclidean object captures these independent observables provides strong evidence that renormalization accounts for the discrepancy between the two formalisms, and establishes a quantitative link between instanton predictions, lattice simulations, and forthcoming empirical tests of vacuum decay.

hep-th↗

arXiv2026

Measuring cosmic bulk flow with kinetic Sunyaev-Zel'dovich velocity reconstruction

Cosmic bulk flow--the volume-averaged peculiar velocity of matter--serves as a fundamental test of the Cosmological Principle when probed on gigaparsec (Gpc) scales. Historically, however, measurements of cosmic bulk flow have been limited to $R\lesssim 100\ h^{-1}{\rm Mpc}$. We present an application of kinetic Sunyaev-Zel'dovich (kSZ) velocity reconstruction to constrain the bulk flow on cosmological scales, over a volume of effective radius $R\sim2000\ h^{-1} {\rm Mpc}$. We use the WISE$\times$SuperCOSMOS and unWISE galaxy catalogs, combined with CMB temperature maps from Planck to reconstruct large-scale velocities in six tomographic bins spanning $0.1\lesssim z \lesssim 1.5$. We place some of the tightest upper limits to date on bulk velocity at $200 \lesssim R\,[h^{-1}{\rm Mpc}]\lesssim 2000$, finding results fully consistent with the $\Lambda$CDM bulk flow expectation. Our unWISE constraints are in strong tension with the CatWISE quasar number-count dipole measurement if that dipole is due to a coherent bulk flow $\sim 370\ {\rm km\,s^{-1}}$ at $R\sim1000\ h^{-1}{\rm Mpc}$. We also derive constraints on the matter power spectrum at low-$k$ ($k\lesssim10^{-3}\, {\rm Mpc}^{-1}$) with low-$z$ ($z\sim 1$) galaxy samples. Alongside these cosmological constraints, we introduce a novel approach to map the optical depth bias--an inherent astrophysical degeneracy in kSZ velocity reconstruction--across different data combinations. Our work bridges the theoretical gap between bulk flow and kSZ-reconstructed velocities, and expands the horizon of bulk velocity measurements out to Gpc scales.

astro-ph.CO↗

arXiv2026

Predictive Synthesis under Sporadic Participation: Evidence from Inflation Density Surveys

Central banks rely on density forecasts from professional surveys to assess inflation risks and communicate uncertainty. A central challenge in using these surveys is irregular participation: forecasters enter and exit, skip rounds, and reappear after long gaps. In the European Central Bank's Survey of Professional Forecasters, turnover and missingness vary substantially over time, causing the set of submitted predictions to change from quarter to quarter. Standard aggregation rules -- such as equal-weight pooling, renormalization after dropping missing forecasters, or ad hoc imputation -- can generate artificial jumps in combined predictions driven by panel composition rather than economic information, complicating real-time interpretation and obscuring forecaster performance. We develop coherent Bayesian updating rules for forecast combination under sporadic participation that maintain a well-defined latent predictive state for each forecaster even when their forecast is unobserved. Rather than relying on renormalization or imputation, the combined predictive distribution is updated through the implied conditional structure of the panel. This approach isolates genuine performance differences from mechanical participation effects and yields interpretable dynamics in forecaster influence. In the ECB survey, it improves predictive accuracy relative to equal-weight benchmarks and delivers smoother and better-calibrated inflation density forecasts, particularly during periods of high turnover.

stat.AP↗

arXiv2026

Billions-Scale Forecast Reconciliation

The problem of combining multiple forecasts of related quantities that obey expected equality and additivity constraints, often referred to a hierarchical forecast reconciliation, is naturally stated as a simple optimization problem. In this paper we explore optimization-based point forecast reconciliation at scales faced by large retailers. We implement and benchmark several algorithms to solve the forecast reconciliation problem, showing efficacy when the dimension of the problem exceeds four billion forecasted values. To the best of our knowledge, this is the largest forecast reconciliation problem, and perhaps on-par with the largest constrained least-squares-problem ever solved. We also make several theoretical contributions. We show that for a restricted class of problems and when the loss function is weighted appropriately, least-squares forecast reconciliation is equivalent to share-based forecast reconciliation. This formalizes how the optimization based approach can be thought of as a generalization of share-based reconciliation, applicable to multiple, overlapping data hierarchies.

stat.ME↗

arXiv2025

The Atacama Cosmology Telescope: Cross-correlation of kSZ and continuity equation velocity reconstruction with photometric DESI LRGs

Over the last year, kinematic Sunyaev--Zel'dovich (kSZ) velocity reconstruction -- the measurement of the large-scale velocity field using the anisotropic statistics of the small-scale kSZ-galaxy overdensity correlation -- has emerged as a statistically significant probe of the large-scale Universe. In this work, we perform a 2-dimensional tomographic reconstruction using ACT DR6 CMB data and DESI legacy luminous red galaxies (LRGs). We measure the cross-correlation of the kSZ-reconstructed velocity $v^{\mathrm{kSZ}}$ with the velocity inferred from the continuity equation applied to the DESI LRGs $v^{\mathrm{cont}}$ at the $\sim 10 \sigma$ level, detecting the signal with an amplitude with respect to our theory of $b_v = 0.339\pm 0.034$. We fit a scale-dependent galaxy bias model to our measurement in order to constrain local primordial non-Gaussianity $f_{\mathrm{NL}}^{\mathrm{loc}}$, finding {$f_{\mathrm{NL}}^{\mathrm{loc}}=-180^{+61}_{-86}$} at 67\% confidence, with $f_{\mathrm{NL}}^{\mathrm{loc}}$ consistent with zero at 95\% confidence. We also measure an auto spectrum at $2.1\sigma$ significance which provides a constraint on $b_v$ of $b_v=0.26_{-0.05}^{+0.11}$, which is consistent with the measurement from the cross spectrum. Our combined measurement is $b_v=0.33\pm0.03$, an $11\sigma$ measurement. We find a good fit of our model to the data in all cases. Finally, we use different ACT frequency combinations to explore foreground contamination, finding no evidence for foreground contamination in our velocity cross correlation. We compare to a similar measurement where $v^{\mathrm{kSZ}}$ is directly cross correlated with the large-scale galaxy field, and find signs of foreground contamination which is contained in the equal-redshift spectra.

astro-ph.CO↗

arXiv2025

Reconstruction of Dark Matter and Baryon Density From Galaxies: A Comparison of Linear, Halo Model and Machine Learning-Based Methods

For many analyses in cosmology it is necessary to reconstruct the likely distribution of unobserved fields, such as dark matter or non-luminous baryons, from observed luminous tracers. The dominant approach in cosmology has been to use the so-called halo model, which assumes radially symmetric profiles centered around luminous tracers such as galaxies. More recently, field-level machine learning methods have been proposed that can learn to estimate the unobserved field after being trained on simulations. However, it is unclear whether machine learning methods indeed significantly improve over linear methods or the halo model. In this paper we make a systematic comparison of different approaches to reconstruct dark matter and non-luminous baryons, from galaxy data using the CAMELS simulations. These simulations are in a $25\ \texttt{Mpc/h}$ box, allowing us to compare performance on the mildly non-linear scales $(k\sim 0.4\ \mathrm{h/Mpc})$ down to the size of individual halos. We find the best results using a combined GNN-CNN approach. We also provide a general analysis and visualization of the relationship of matter, non-luminous baryons, halos, and galaxies in these simulations to interpret our results.

astro-ph.CO↗

arXiv2024

Reconstruction of Continuous Cosmological Fields from Discrete Tracers with Graph Neural Networks

We develop a hybrid GNN-CNN architecture for the reconstruction of 3-dimensional continuous cosmological matter fields from discrete point clouds, provided by observed galaxy catalogs. Using the CAMELS hydrodynamical cosmological simulations we demonstrate that the proposed architecture allows for an accurate reconstruction of both the dark matter and electron density given observed galaxies and their features. Our approach includes a learned grid assignment scheme that improves over the traditional cloud-in-cell method. Our method can improve cosmological analyses in situations where non-luminous (and thus unobservable) continuous fields need to be estimated from luminous (observable) discrete point cloud tracers.

astro-ph.CO↗

arXiv2024

The Atacama Cosmology Telescope: Large-scale velocity reconstruction with the kinematic Sunyaev--Zel'dovich effect and DESI LRGs

The kinematic Sunyaev--Zel'dovich (kSZ) effect induces a non-zero density-density-temperature bispectrum, which we can use to reconstruct the large-scale velocity field from a combination of cosmic microwave background (CMB) and galaxy density measurements, in a procedure known as ``kSZ velocity reconstruction''. This method has been forecast to constrain large-scale modes with future galaxy and CMB surveys, improving their measurement beyond what is possible with the galaxy surveys alone. Such measurements will enable tighter constraints on large-scale signals such as primordial non-Gaussianity, deviations from homogeneity, and modified gravity. In this work, we demonstrate a statistically significant measurement of kSZ velocity reconstruction for the first time, by applying quadratic estimators to the combination of the ACT DR6 CMB+kSZ map and the DESI LRG galaxies (with photometric redshifts) in order to reconstruct the velocity field. We do so using a formalism appropriate for the 2-dimensional projected galaxy fields that we use, which naturally incorporates the curved-sky effects important on the largest scales. We find evidence for the signal by cross-correlating with an external estimate of the velocity field from the spectroscopic BOSS survey and rejecting the null (no-kSZ) hypothesis at $3.8\sigma$. Our work presents a first step towards the use of this observable for cosmological analyses.

astro-ph.CO↗

arXiv2024

Revisiting Dark Photon Constraints from CMB Spectral Distortions

Spectral distortions of the cosmic microwave background (CMB) provide stringent constraints on energy and entropy production in the post-BBN (Big Bang Nucleosynthesis) era. This has been used to constrain dark photon models with COBE/FIRAS and forecast the potential gains with future CMB spectrometers. Here, we revisit these constraints by carefully considering the photon to dark photon conversion process and evolution of the distortion signal. Previous works only included the effect of CMB energy density changes but neglected the change to the photon number density. We clearly define the dark photon distortion signal and show that in contrast to previous analytic estimates the distortion has an opposite sign and a $\simeq 1.5$ times larger amplitude. We furthermore extend the treatment into the large distortion regime to also cover the redshift range $\simeq 2\times 10^6-4\times 10^7$ between the $\mu$-era and the end of BBN using CosmoTherm. This shows that the CMB distortion constraints for dark photon masses in the range $10^{-4}\,{\rm eV}\lesssim m_{\rm dp}\lesssim 10^{-3}\,{\rm eV}$ were significantly underestimated. We demonstrate that in the small distortion regime the distortion caused by photon to dark photon conversion is extremely close to a $\mu$-type distortion independent of the conversion redshift. This opens the possibility to study dark photon models using CMB distortion anisotropies and the correlations with CMB temperature anisotropies as we highlight here.

astro-ph.CO↗

arXiv2024

Constraints on axions from patchy screening of the cosmic microwave background

The resonant conversion of cosmic microwave background (CMB) photons into axions within large-scale structure induces an anisotropic spectral distortion in CMB temperature maps. Applying state-of-the-art foreground cleaning techniques to $\textit{Planck}$ CMB observations, we construct maps of axion-induced "patchy screening" of the CMB. We cross-correlate these maps with data from the $\textit{unWISE}$ galaxy survey and find no evidence of axions. We constrain the axion-photon coupling, $g_{a\gamma\gamma} \lesssim 2 \times 10^{-12}~{\rm GeV}^{-1}$, at the 95% confidence level for axion masses in the range $10^{-13}~{\rm eV} \lesssim m_a \lesssim 10^{-12}~{\rm eV}$. These constraints are competitive with the tightest astrophysical axion limits in this mass range and are inferred from robust population-level statistics, which makes them complementary to existing searches that rely on modeling of individual systems.

astro-ph.CO↗

arXiv2024

Constraints on cosmology beyond $\Lambda$CDM with kinetic Sunyaev Zel'dovich velocity reconstruction

Kinetic Sunyaev Zel'dovich velocity reconstruction uses the statistically anisotropic cross-correlation between cosmic microwave background (CMB) temperature anisotropies and a galaxy survey to reconstruct the remotely observed CMB dipole. Using a reconstruction based on data from $\textit{Planck}$ and unWISE, we rule out non-linear Gpc-scale voids, provide the tightest constraint on the intrinsic dipole ($<14 \ {\rm km/s}$ at $68\%$ confidence), rule out matter-radiation isocurvature as an explanation of discrepancies between the measured CMB and galaxy number count dipoles, and constrain the amplitude of local-type primordial non-Gaussianity ($-220\lesssim f_{\rm NL}\lesssim 136$ at $68\%$ confidence) and compensated isocurvature ($-147\lesssim A_{\rm CIP} \lesssim 281$ at $68\%$ confidence). This representative set of constraints on beyond-$\Lambda$CDM scenarios demonstrates the breadth of fundamental science possible with measurements of secondary CMB anisotropies such as the kinetic Sunyaev Zel'dovich effect.

astro-ph.CO↗

arXiv2024

Dark photon limits from patchy dark screening of the cosmic microwave background

Dark photons that kinetically mix with the Standard Model photon give rise to new spectral anisotropies (patchy dark screening) in the cosmic microwave background (CMB) due to conversion of photons to dark photons within large-scale structure. We utilize predictions for this patchy dark screening signal to provide the tightest constraints to date on the dark photon kinetic mixing parameter ($\varepsilon \lesssim 4\times 10^{-8}$ (95% confidence level)) over the mass range $10^{-13} \,\, {\rm eV} \lesssim m_{A^\prime} \lesssim 10^{-11}$ eV, almost an order of magnitude stronger than previous limits, by applying state-of-the-art component separation techniques to the cross-correlation of $\textit{Planck}$ CMB and $\textit{unWISE}$ galaxy survey data.

hep-ph↗

arXiv2024

Axion-Induced Patchy Screening of the Cosmic Microwave Background

Cosmic Microwave Background (CMB) photons can undergo resonant conversion into axions in the presence of magnetized plasma distributed inside non-linear large-scale structure (LSS). This process leads to axion-induced patchy screening: secondary temperature and polarization anisotropies with a characteristic non-blackbody frequency dependence that are strongly correlated with the distribution of LSS along our past light cone. We compute the axion-induced patchy screening contribution to two- and three- point correlation functions that include CMB anisotropies and tracers of LSS within the halo model. We use these results to forecast the sensitivity of existing and future surveys to photon-axion couplings for axion masses between $2\times 10^{-13}$ eV and $3\times 10^{-12}$ eV, using a combination of empirical estimates from Planck data of the contribution from instrumental noise and foregrounds as well as modeled contributions on angular scales only accessible with future datasets. We demonstrate that an analysis using Planck and the unWISE galaxy catalogue would be complementary to the most sensitive existing astrophysical axion searches, probing couplings as small as $3\times 10^{-12} \, {\rm GeV}^{-1}$, while observations from a future survey such as CMB-S4 could extend this reach by almost an additional order of magnitude.

hep-ph↗

arXiv2024

Kinetic Sunyaev Zel'dovich velocity reconstruction from Planck and unWISE

The kinetic Sunyaev Zel'dovich (kSZ) effect is a blackbody cosmic microwave background (CMB) temperature anisotropy induced by Thomson scattering off free electrons in bulk motion with respect to the CMB rest frame. The statistically anisotropic cross-correlation between the CMB and galaxy surveys induced by the kSZ effect encodes the radial bulk velocity (more generally, the remote dipole field), which can be efficiently reconstructed using a quadratic estimator. Here, we develop a quadratic estimator for the remote dipole field for use with data from the Planck satellite and the unWISE galaxy redshift catalog. With this data combination, we forecast a signal-to-noise of order unity within $\Lambda$CDM assuming a simple model for the distribution of free electrons. Using reconstructions based on individual frequency temperature maps and a variety of component separated CMB maps, we characterize the impact of foregrounds and systematics. The dominant contaminant is a coupling between the cosmic infrared background and large-scale galaxy survey systematics. We develop a method to minimize this effect, and demonstrate that after doing so the reconstructions are consistent with the expected level and properties of reconstruction noise. We use this reconstruction to constrain the multiplicative optical depth bias characterizing the amplitude of the remote dipole field to $b_v < 1.04$ at $68 \%$ confidence. Our fiducial signal model with $b_v =1$ is consistent with this measurement. Our results support an optimistic future for kSZ velocity reconstruction with near-term datasets.

astro-ph.CO↗

arXiv2024

Improving Photometric Galaxy Clustering Constraints With Cross-Bin Correlations

Clustering studies in current photometric galaxy surveys focus solely on auto-correlations, neglecting cross-correlations between redshift bins. We evaluate the potential advantages and drawbacks of incorporating cross-bin correlations in Fisher forecasts for the Dark Energy Survey (DES) and the forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST). Our analysis considers the impact of including redshift space distortions (RSD) and magnification in model predictions, as well as systematic uncertainties in photometric redshift distributions (photo-$z$). While auto-correlations alone suffer from a degeneracy between the amplitude of matter fluctuations ($\sigma_8$) and galaxy bias parameters, accounting for RSD and magnification in cross-correlations helps break this degeneracy - although more weakly than the degeneracy breaking expected from a combined analysis with other observables. Incorporating cross-bin correlations does not significantly increase sensitivity to photo-$z$ systematics, addressing previous concerns, and self-calibrates photo-$z$ systematics, reducing errors on photo-$z$ nuisance parameters. We suggest that the benefits of including cross-correlations in future photometric galaxy clustering analyses outweigh the risks, but caution that careful evaluation is necessary as more realistic pictures of surveys' precision and systematic error budgets develop.

astro-ph.CO↗

arXiv2024

Analog vacuum decay from vacuum initial conditions

Ultracold atomic gases can undergo phase transitions that mimic relativistic vacuum decay, allowing us to empirically test early-Universe physics in tabletop experiments. We investigate the physics of these analog systems, going beyond previous analyses of the classical equations of motion to study quantum fluctuations in the cold-atom false vacuum. We show that the fluctuation spectrum of this vacuum state agrees with the usual relativistic result in the regime where the classical analogy holds, providing further evidence for the suitability of these systems for studying vacuum decay. Using a suite of semiclassical lattice simulations, we simulate bubble nucleation from this analog vacuum state in a 1D homonuclear potassium-41 mixture, finding qualitative agreement with instanton predictions. We identify realistic parameters for this system that will allow us to study vacuum decay with current experimental capabilities, including a prescription for efficiently scanning over decay rates, and show that this setup will probe the quantum (rather than thermal) decay regime at temperatures $T\lesssim10\,\mathrm{nK}$. Our results help lay the groundwork for using upcoming cold-atom experiments as a new probe of nonperturbative early-Universe physics.

cond-mat.quant-gas↗