arXiv subjects

Eric V. Linder

Publications and source records attributed to Eric V. Linder.

At least 37 records · Page 2Linked to original sources

arXiv2023

Connecting Primordial Gravitational Waves and Dark Energy

Cosmic acceleration manifested in the early universe as inflation, generating primordial gravitational waves detectable in the cosmic microwave background (CMB) radiation. Cosmic acceleration is occurring again at present as dark energy, detectable in cosmic distance and structure surveys. We explore the intriguing idea of connecting the two occurrences through quintessential inflation by an $α$-attractor potential without a cosmological constant. For this model we demonstrate robustness of the connection $1+w_0\approx 4/(3N^2r)$ between the present day dark energy equation of state parameter $w_0$ and the primordial tensor to scalar ratio $r$ for a wide range of initial conditions. Analytics and numerical solutions produce current thawing behavior, resulting in a tight relation $w_a\approx-1.53(1+w_0)\approx -0.2\,(4\times 10^{-3}/r)$. Upcoming CMB and galaxy redshift surveys can test this consistency condition. Within this model, lack of detection of a dark energy deviation from $Λ$ predicts a higher $r$, and lack of detection of $r$ predicts greater dark energy dynamics.

astro-ph.CO↗

arXiv2023

Benchmarks of Dark Energy

Dark energy is a premier mystery of physics, both theoretical and experimental. As we look to develop plans for high energy physics over the next decade, within a two decade view, we consider benchmarks for revealing the nature of dark energy. We conclude, based on fundamental physical principles detailed below, that understanding will come from experiments reaching key benchmarks: $\bullet\ σ(w_a)<2.5σ(w_0)$ $\bullet\ σ(w_0)<0.02$ $ \bullet\ σ(ρ_{\rm de}/ρ_{\rm crit})<(1/3)ρ_Λ/ρ_{\rm crit}$ for all redshifts $z<5$ where the dark energy equation of state $w(a)=w_0+w_a(1-a)$. Beyond the cosmic expansion history we also discuss benchmarks for the cosmic growth history appropriate for testing classes of gravity theories. All benchmarks can be achieved by a robust Stage 5 program, using extensions of existing probes plus the highly complementary, novel probe of cosmic redshift drift.

astro-ph.CO↗

arXiv2023

Testing Cosmology with Double Source Lensing

Double source lensing provides a dimensionless ratio of distance ratios, a "remote viewing" of cosmology through distances relative to the gravitational lens, beyond the observer. We use this to test the cosmological framework, particularly with respect to spatial curvature and the distance duality relation. We derive a consistency equation for constant spatial curvature, allowing not only the investigation of flat vs curved but of the Friedmann-Lemaître-Robertson-Walker framework itself. For distance duality, we demonstrate that the evolution of the lens mass profile slope must be controlled to $\gtrsim5$ times tighter fractional precision than a claimed distance duality violation. Using LENSPOP forecasts of double source lensing systems in Euclid and LSST surveys we also explore constraints on dark energy equation of state parameters and any evolution of the lens mass profile slope.

astro-ph.CO↗

arXiv2023

Stopping to Reflect: Asymptotic Static Moving Mirrors as Quantum Analogs of Classical Radiation

Radiation from an accelerating charge is a basic process that can serve as an intersection between classical and quantum physics. We present two exactly soluble electron trajectories that permit analysis of the radiation emitted, exploring its time evolution and spectrum by analogy with the moving mirror model of the dynamic Casimir effect. These classical solutions are finite energy, rectilinear (nonperiodic), asymptotically zero velocity worldlines with corresponding quantum analog beta Bogolyubov coefficients. One of them has an interesting connection to uniform acceleration and Leonardo da Vinci's water pitcher experiment.

quant-ph↗

arXiv2023

A Whole Cosmology View of the Hubble Constant

The Hubble constant $H_0$ is the value of the cosmic expansion rate at one time (the present), and cannot be adjusted successfully without taking into account the entire expansion history and cosmology. We outline some conditions, that if not quite ``no go'' are ``no thanks'', showing that changing the expansion history, e.g. employing dynamical dark energy, cannot reconcile disparate deductions of $H_0$ without upsetting some other cosmological measurement.

astro-ph.CO↗

arXiv2022

Constraining Scale Dependent Growth with Redshift Surveys

Ongoing and future redshift surveys have the capability to measure the growth rate of large scale structure at the percent level over a broad range of redshifts, tightly constraining cosmological parameters. Beyond general relativity, however, the growth rate in the linear density perturbation regime can be not only redshift dependent but scale dependent, revealing important clues to modified gravity. We demonstrate that a fully model independent approach of binning the gravitational strength $G_{\rm eff}(k,z)$ matches scalar-tensor results for the growth rate $fσ_8(k,z)$ to $0.02\%$-$0.27\%$ rms accuracy. For data of the quality of the Dark Energy Spectroscopic Instrument (DESI) we find the bin values can be constrained to 1.4\%-28\%. We also explore the general scalar-tensor form, constraining the amplitude and past and future scalaron mass/shape parameters. Perhaps most interesting is the strong complementarity of low redshift peculiar velocity data with DESI-like redshift space distortion measurements, enabling improvements up to a factor 6-7 on 2D joint confidence contour areas. Finally, we quantify some issues with gravity parametrizations that do not include all the key physics.

astro-ph.CO↗

arXiv2022

Upon the horizon's verge: Thermal particle creation between and approaching horizons

Quantum particle creation from spacetime horizons, or accelerating boundaries in the dynamical Casimir effect, can have an equilibrium, or thermal, distribution. Using an accelerating boundary in flat spacetime (moving mirror), we investigate the production of thermal energy flux despite non-equilibrium accelerations, the evolution between equilibrium states, and the "interference" between horizons. In particular, this allows us to give a complete solution to the particle spectrum of the accelerated boundary correspondence with Schwarzschild-de Sitter spacetime.

gr-qc↗

arXiv2022

Cosmic Acceleration with and without Limits

A novel, interesting class of scalar-tensor gravity theories is those with a limit on the field motion, where the scalar field either goes to a constant acceleration or stops accelerating and goes to a constant velocity. We combine these with the ability to dynamically cancel a high energy cosmological constant, e.g. through the well tempered or self tuning approaches. One can successfully have a cosmic expansion history with a matter dominated epoch and late time acceleration despite a large cosmological constant, although the late time de Sitter limit may be unstable. Pole models, such as in a Dirac-Born-Infeld action, are of particular interest for a cosmic speed limit.

gr-qc↗

arXiv2022

Report of the Topical Group on Dark Energy and Cosmic Acceleration: Complementarity of Probes and New Facilities for Snowmass 2021

The mechanism(s) driving the early- and late-time accelerated expansion of the Universe represent one of the most compelling mysteries in fundamental physics today. The path to understanding the causes of early- and late-time acceleration depends on fully leveraging ongoing surveys, developing and demonstrating new technologies, and constructing and operating new instruments. This report presents a multi-faceted vision for the cosmic survey program in the 2030s and beyond that derives from these considerations. Cosmic surveys address a wide range of fundamental physics questions, and are thus a unique and powerful component of the HEP experimental portfolio.

astro-ph.CO↗

arXiv2022

The MegaMapper: A Stage-5 Spectroscopic Instrument Concept for the Study of Inflation and Dark Energy

In this white paper, we present the MegaMapper concept. The MegaMapper is a proposed ground-based experiment to measure Inflation parameters and Dark Energy from galaxy redshifts at $2<z<5$. In order to achieve path-breaking results with a mid-scale investment, the MegaMapper combines existing technologies for critical path elements and pushes innovative development in other design areas. To this aim, we envision a 6.5-m Magellan-like telescope, with a newly designed wide field, coupled with DESI spectrographs, and small-pitch robots to achieve multiplexing of at least 26,000. This will match the expected achievable target density in the redshift range of interest and provide a 10x capability over the existing state-of the art, without a 10x increase in project budget.

astro-ph.IM↗

arXiv2022

A Spectroscopic Road Map for Cosmic Frontier: DESI, DESI-II, Stage-5

In this white paper, we present an experimental road map for spectroscopic experiments beyond DESI. DESI will be a transformative cosmological survey in the 2020s, mapping 40 million galaxies and quasars and capturing a significant fraction of the available linear modes up to z=1.2. DESI-II will pilot observations of galaxies both at much higher densities and extending to higher redshifts. A Stage-5 experiment would build out those high-density and high-redshift observations, mapping hundreds of millions of stars and galaxies in three dimensions, to address the problems of inflation, dark energy, light relativistic species, and dark matter. These spectroscopic data will also complement the next generation of weak lensing, line intensity mapping and CMB experiments and allow them to reach their full potential.

astro-ph.CO↗

arXiv2022

Double Source Lensing Probing High Redshift Cosmology

Double source lensing, with two sources lensed by the same foreground galaxy, involves the distance between each source and the lens and hence is a probe of the universe away from the observer. The double source distance ratio also reduces sensitivity to the lens model and has good complementarity with standard distance probes. We show that using this technique at high redshifts $z>1$, to be enabled by data from the Euclid satellite and other surveys, can give insights on dark energy, both in terms of $w_0$-$w_a$ and redshift binned density. We find a dark energy figure of merit of 245 from combination of 256 double source systems with moderate quality cosmic microwave background and supernova data. Using instead five redshift bins between $z=1.1$-5, we could detect the dark energy density out to $z\approx5$, or make measurements ranging between 31$σ$ and 2.5$σ$ of its values in the bins.

astro-ph.CO↗

arXiv2022

Deep Learning Unresolved Lensed Lightcurves

Gravitationally lensed sources may have unresolved or blended multiple images, and for time varying sources the lightcurves from individual images can overlap. We use convolutional neural nets to both classify the lightcurves as due to unlensed, double, or quad lensed sources and fit for the time delays. Focusing on lensed supernova systems with time delays $Δt\gtrsim6$ days, we achieve 100\% precision and recall in identifying the number of images and then estimating the time delays to $σ_{Δt}\approx1$ day, with a $1000\times$ speedup relative to our previous Monte Carlo technique. This also succeeds for flux noise levels $\sim10\%$. For $Δt\in[2,6]$ days we obtain 94--98\% accuracy, depending on image configuration. We also explore using partial lightcurves where observations only start near maximum light, without the rise time data, and quantify the success.

astro-ph.IM↗

arXiv2022

A novel approach for calculating galaxy rotation curves using spaxel cross-correlation and iterative smoothing

Precise measurements of the internal dynamics of galaxies have proven of great importance for understanding the internal dark matter distribution of galaxies. We present a novel method for measuring the line-of-sight (LOS) velocities across the face of galaxies by cross-correlation of spectral pixels (spaxels) and an iterative method of smoothing. On simulated data the method can accurately recover the input LOS velocities for different types of spectra (absorption line dominated, emission line dominated, and differing shapes of the continuum), and can handle stellar population radial gradients. Most important of all, it continues to provide reliable measurements of LOS velocities with reasonable uncertainties even when the spectra are very low signal-to-noise (approaching $\sim 1$), which is a challenge for traditional template-fitting approaches. We apply our method to data from a real MaNGA galaxy as a demonstration and find promising results with good precision. This novel approach can be complementary to existing methods primarily based on template fitting.

astro-ph.CO↗

arXiv2022

Isogrowth Cosmology (and How to Map the Universe)

While general relativity ties together the cosmic expansion history and growth history of large scale structure, beyond the standard model these can have independent behaviors. We derive expressions for cosmologies with identical growth histories but different expansion histories, or other deviations. This provides a relation for isogrowth cosmologies, but also highlights in general the need for observations to measure each of the growth, expansion, gravity, and dark matter property histories.

astro-ph.CO↗

arXiv2022

Out of One, Many: Distinguishing Time Delays from Lensed Supernovae

Gravitationally lensed Type Ia supernovae are an emerging probe with great potential for constraining dark energy, spatial curvature, and the Hubble constant. The multiple images and their time delayed and magnified fluxes may be unresolved, however, blended into a single lightcurve. We demonstrate methods without a fixed source template matching for extracting the individual images, determining whether there are one (no lensing) or two or four (lensed) images, and measuring the time delays between them that are valuable cosmological probes. We find 100% success for determining the number of images for time delays greater than $\sim10$ days.

astro-ph.CO↗

arXiv2022

Well Tempered Cosmology: Scales

Well tempered cosmology provides a well defined path for obtaining cosmology with a low energy cosmic acceleration despite a high (Planck) energy cosmological constant $Λ$, through a scalar field dynamically canceling $Λ$. We explore relations between the mass scales entering the various Horndeski gravity terms, and focus on the cases of only one or only two mass scales, obtaining general solutions for the form of the action. The resulting cosmology can be natural and viable, and as one of the only paths to dealing with the cosmological constant problem it has a rationale to be a benchmark cosmology.

gr-qc↗

arXiv2021

Horndessence: $Λ$CDM Cosmology from Modified Gravity

Rather than obtaining cosmic acceleration with a scalar field potential (quintessence) or noncanonical kinetic term (k-essence), we can do it purely through a modified gravity braiding of the scalar and metric, i.e. the $G_3$ Horndeski action term. Such "Horndessence" allows an exact $Λ$CDM cosmological expansion without any cosmological constant, and by requiring shift symmetry we can derive the exact form of $G_3$. We find that this route of deriving $G_3(X)$ leads to a functional form far from the usual simple assumptions such as a power law. Horndessence without any kinetic term or potential has the same number of parameters as $Λ$CDM and makes an exact prediction for the expansion history ($Λ$CDM) and modified gravity cosmic growth history; we show the viable gravitational strength $G_{\rm eff}(a)$ and growth rate $fσ_8(a)$. The simplest versions of the theory fail soundness criteria, but we learn interesting lessons along the way, in particular about robust parametrization, and indicate possible sound extensions.

gr-qc↗