arXiv subjects

Eric V. Linder

Publications and source records attributed to Eric V. Linder.

At least 19 recordsLinked to original sources

arXiv2026

Mass-Varying Neutrinos from an Inverse Symmetron

Neutrinos enter cosmology in different ways and are constrained by distinct observational probes across different epochs: as a relativistic species at high redshift, as a massive but clustering-suppressing component at low redshift, and as a particle physics observable in laboratory experiments. Low (verging on negative) bounds on neutrino mass from galaxy surveys motivate exploration of models where neutrinos may couple to dark energy, causing their mass to vary over cosmic evolution. If the coupling involves an inverse phase transition (symmetry broken, rather than restored, as neutrinos become nonrelativistic) this can tame instabilities in neutrino growth, appear as a lower neutrino mass in galaxy surveys, and add extra suppression to the matter power spectrum. We find that the late-time decoupling shuts down the fifth force and inhibits the excessive growth of neutrino perturbations, thereby eliminating linear-regime instabilities. The model may potentially address the Hubble tension via an early dark energy component localized around the time of recombination.

astro-ph.CO↗

arXiv2026

Planckian Gravitons from an Imaginary-Time Clock

We present a simple derivation of the exact Planck spectrum of the quadrupole radiation from point masses moving apart nonrelativistically, essentially an analog for gravitational radiation. The standard Einstein quadrupole radiation formula gives emitted power proportional to the square of the third derivative of $x(t)^2$. In our moving-mass picture, imaginary-time periodicity appears as a product-log trajectory of a quadrupole source. In the frequency domain, the power becomes proportional to the Planck distribution, $\omega^3/(e^{2\pi c\omega/\kappa}-1)$. The resulting Planckian graviton energy spectrum has finite total energy and finite graviton number. The emitted spectrum is purely kinematic in origin: no equilibrium, horizon, or stochastic source is assumed.

gr-qc↗

arXiv2026

Charging Across the Phantom Divide with Modified Gravity

Cosmology where the effective dark energy crosses $w=-1$ can be realized in Horndeski gravity with shift symmetric terms plus a linear potential. We highlight the special role of the nearly conserved scalar charge. The theory is highly predictive for the early phantom behavior and we identify three ways to cross $w=-1$. None of them recreate conditions indicated by current data very well. The major lesson is that such modified gravity with a potential lacking a cosmological constant and only crossing $w=-1$ once (hence the less elaborate models) has difficulty fitting current data. We provide an online interactive application solving the system of evolution equations, for the reader to explore various scenarios at will.

gr-qc↗

arXiv2026

Finding Strongly Lensed Supernovae from Blended Light Curves

We present a model-independent, photometry-only framework for identifying strongly lensed supernovae when multiple images are unresolved and blended into a single point source. Building on the simulation-based methodology of Bag et al. (2021), we apply this approach to real Zwicky Transient Facility (ZTF) data using a validation sample of spectroscopically confirmed Type Ia supernovae. The method models the observed flux as a superposition of two time-shifted components, and Bayesian inference is used to estimate the relative scaling and time delay. Applying this framework to 445 well-converged supernovae, we find that only a single object satisfies the selection criteria when adopting a conservative threshold of $Δt \ge 12$ days, corresponding to a false positive fraction of $1/445 \approx 0.22\%$. A laxer threshold of $Δt \ge 10$ days yields fourteen objects, for a false positive fraction of $3.15\%$. The method provides a scalable and model-independent first-stage filter for identifying lens-like candidates in large time-domain surveys such as the Rubin Observatory's Legacy Survey of Space and Time (LSST).

astro-ph.IM↗

arXiv2026

Self-Reflection in a Moving Mirror

We present an analytic flat-spacetime accelerating boundary analog of Hawking-type emission that possesses infinite asymptotic acceleration (and radial acceleration in the black hole analog) but finite total radiated energy (and zero surface gravity in the black hole analog). We perform a unified study of its scattering symmetry, horizon formation, asymptotically extreme acceleration, finite total radiated energy, and the distinction between local energy flux and global particle production within a single closed-form model. The particle spectrum, energy spectrum, and equivalent spacetime metric are derived, revealing an interesting mix of normal and extremal black hole properties.

gr-qc↗

arXiv2026

When One-Parameter Dark Energy Makes Neutrinos Physical Again

A puzzling implication of current data interpreted in the $Λ$CDM cosmology is the preference for a negative sum of neutrino masses. Moving to $w_0w_a$CDM brings an appreciable fraction of the neutrino mass posterior back to positive values, while the constant equation-of-state dark energy case $w$CDM does not. We investigate a variety of one-parameter dark energy equations of state (DE EoS), each variation with particular physical properties, to understand whether a two-parameter DE EoS is required to bring the neutrino mass positive. The conclusion is that certain one-parameter DE EoS can suffice, implying that the data are pointing toward physical characteristics rather than a broad degeneracy. The required characteristics are identified as phantom dark energy at high redshift, crossing $w=-1$ at lower redshift.

astro-ph.CO↗

arXiv2025

Cosmology after Phantom Crossing by Horndeski Gravity

One possible way to explain the observed effective dark energy equation of state crossing $w=-1$ (the phantom divide) is through modified gravity. A key point is to not view the expansion history in isolation but to take into account the other gravitational impacts on growth of large scale structure, lensing, etc. Within shift symmetric Horndeski gravity this implies three main paths for the late time cosmic expansion. All require unusual kinetic structure and we analyze their various implications for how $w$ should behave after phantom crossing.

astro-ph.CO↗

arXiv2025

Null Impact of the Null Energy Condition in Current Cosmology

We clarify the role of the oft-misunderstood Null Energy Condition (NEC) in the context of the current cosmological data. In particular, the NEC implies the sum of the total energy density and pressure satisfies $ρ_{tot}+P_{tot} \ge 0$; the energy conditions do not apply separately to individual components of the cosmological fluid. Consequently, we show that under the current best-fit cosmological model no violation of the NEC takes place, past or future. Further, growth in the energy density of an individual component cannot be used to signal violation of the NEC. We illustrate these points with a worked example whereby misestimation of the matter density leads to a phase during which $ρ_{de} + P_{de} < 0$ for the effective dark energy, followed by a phantom crossing and subsequent $ρ_{de} + P_{de} > 0$. At no time is the NEC violated. We also introduce ``elephant'' and ``chimera'' classes of physics for crossing $w_{de}=-1$.

astro-ph.CO↗

arXiv2025

Particle creation from entanglement entropy

We investigate how entanglement entropy can drive particle creation, deriving explicit relations between entropy and the radiated particle spectrum, the total number of particles, and the total energy. Particle production is computed for scenarios that include accelerated motion, black hole evaporation, and beta decay, validating against known results while also extending them. We focus primarily on the low-entropy limit (analogous to non-relativistic motion), but also examine cases of significant particle production arising from harmonic cycles. The results establish an explicit operational link between information flow and matter creation, providing a concrete demonstration of 'it from bit'.

quant-ph↗

arXiv2025

Uplifting, Depressing, and Tilting Dark Energy

Current data in the form of baryon acoustic oscillation, supernova, and cosmic microwave background distances prefer a cosmology that accelerates more strongly than $Λ$CDM at $z\approx0.5-1.5$, and more weakly at $z\lesssim0.5$. We examine dark energy physics that can accommodate this, showing that interactions (decays, coupling to matter, nonminimal coupling to gravity) fairly generically tend not to give a satisfactory solution (in terms of fitting both distances and growth) even if they enable the effective dark energy equation of state to cross $w=-1$. To fit the cosmological data it appears the dark energy by itself must cross $w=-1$, a highly unusual physical behavior.

astro-ph.CO↗

arXiv2025

Through the Looking-Glass, and What AdS Found There: quantum particle production with a Whittaker spectrum

Parity-inverted anti-de Sitter space -- ``flipped AdS'' -- is studied through the accelerating boundary correspondence of a moving mirror trajectory. The particle production exhibits positive energy flux and a finite total energy (both unlike AdS). The particle spectrum is of Whittaker form, with some similarities to a Planck thermal spectrum. We also derive the corresponding spacetime metric, with similarities to regular de Sitter space, but exhibiting a tower of repeated causal regions with horizons.

hep-th↗

arXiv2025

Cosmic Acceleration from Nothing

We demonstrate that if the universe started as a vacuum fluctuation rather than from a singular Big Bang state, the universe must have a late-time cosmic acceleration. This is required by a ``cosmological sum rule'' derived using the Schwarzian form of the Friedmann equations. We discuss possible connections to conformal and Möbius transformations, and also compute that the best fit present cosmic data is consistent with the necessary crossing of the Schwarzian through zero having occurred (while it would not yet have happened in a $Λ$CDM cosmology).

gr-qc↗

arXiv2024

Model independent approach for calculating galaxy rotation curves for low $S/N$ MaNGA galaxies

Internal kinematics of galaxies, traced through the stellar rotation curve or two dimensional velocity map, carry important information on galactic structure and dark matter. With upcoming surveys, the velocity map may play a key role in the development of kinematic lensing as an astrophysical probe. We improve techniques for extracting velocity information from integral field spectroscopy at low signal-to-noise ($S/N$), without a template, and demonstrate substantial advantages over the standard Penalized PiXel-Fitting method (pPXF) approach. Robust rotation curves can be derived down to $S/N\approx 2$ using our method.

astro-ph.GA↗

arXiv2024

Interpreting Dark Energy Data Away from $Λ$

Dark energy away from a cosmological constant $Λ$ -- like early universe inflation that ends -- can be understood in terms of well defined physical behaviors. These guide dark energy into thawing or freezing classes, with $w_0$--$w_a$ arising as a physical calibration of the phase space. Other regions of phase space -- zones of avoidance -- require violation of some basic principle. We explore these cases, drawing a direct analogy with how nonGaussianity in inflation can add physics beyond standard dynamics. We examine the physics implications if the best fit of current data is taken to be truth, outlining four properties, and investigate the reality of phantom crossing $w=-1$, finding it significantly favored.

astro-ph.CO↗

arXiv2024

Testing $α$-attractor quintessential inflation against CMB and low-redshift data

Due to universality and attractor properties, $α$-attractor quintessential inflation establishes direct relations between inflationary observables such as the scalar tilt $n_s$ and the tensor-to-scalar ratio $r$, and late-time dark energy equation of state parameters $w_0$ and $w_a$. In this work, we examine three different physically motivated regimes, considering complete freedom in the parameter $α$, models inspired by supergravity where $α$ takes on values up to $α=7/3$, and Starobinsky inflation ($α=1$). We investigate the consistency and constraints imposed by Cosmic Microwave Background measurements from the Planck satellite, B-mode polarization data from the BICEP/Keck collaboration, and low-redshift observations. Additionally, we consider small-scale CMB measurements released by the Atacama Cosmology Telescope, which give results approaching the Harrison-Zel'dovich spectrum ($n_s \approx 1$). Here $α$-attractors lead to an improved fit over $Λ$CDM. For the large-scale CMB measurements, $α\gtrsim2$ models can provide equally good fits as $Λ$CDM.

astro-ph.CO↗

arXiv2024

IR-finite thermal acceleration radiation

A charge accelerating in a straight line following the Schwarzschild-Planck moving mirror motion emits thermal radiation for a finite period. Such a mirror motion demonstrates quantum purity and serves as a direct analogy of a black hole with unitary evolution and complete evaporation. Extending the analog to classical electron motion, we derive the emission spectrum, power radiated, and finite total energy and particle count, with particular attention to the thermal radiation limit. This potentially opens the possibility of a laboratory analog of black hole evaporation.

gr-qc↗

arXiv2023

Model Independent Dark Matter Properties from Cosmic Growth

Dark matter dominates the matter budget of the universe but its nature is unknown. Deviations from the standard model, where dark matter clusters with the same gravitational strength as baryons, and has the same pressureless equation of state as baryons, can be tested by cosmic growth measurements. We take a model independent approach, allowing deviations in bins of redshift, and compute the constraints enabled by ongoing cosmic structure surveys through redshift space distortions and peculiar velocities. These can produce constraints at the $3-14\%$ level in four independent redshift bins over $z=[0,4]$.

astro-ph.CO↗

arXiv2023

Model Independent Reconstruction of Galaxy Stellar Velocity Map

We develop a model independent, robust method for determining galaxy rotation velocities across a 2D array of spaxels from an integral field spectrograph. Simulations demonstrate the method is accurate down to lower spectral signal-to-noise than standard methods: 99\% accurate when median $S/N=4$. We apply it to MaNGA data to construct the galaxy velocity map and galaxy rotation curve. We also develop a highly efficient cubic smoothing approach that is $25\times$ faster computationally and only slightly less accurate. Such model independent methods could be useful in studying dark matter properties without assuming a galaxy model.

astro-ph.CO↗