arXiv subjects

Alisha Marriott-Best

Publications and source records attributed to Alisha Marriott-Best.

5 recordsLinked to original sources

arXiv2026

Impact of Scale-dependent Primordial Non-Gaussianity on Scalar-induced Gravitational Waves

Scalar-induced gravitational waves (SIGWs) probe primordial curvature perturbations beyond cosmic microwave background scales, while primordial black holes (PBHs) probe the rare tail of the same statistics. We ask whether SIGW morphology can reveal scale-dependent primordial non-Gaussianity. We adopt the internal-leg separable kernel, $\mathcal F_{\rm NL}(\mathbf{k};\mathbf q,\mathbf{k}-\mathbf q)=\bar f_{\rm NL}f(q)f(\lVert\mathbf{k}-\mathbf q\rVert)$, and compute Gaussian, reducible, and connected contributions through $\mathcal O(\bar f_{\rm NL}^{4})$ in the second-order tensor-source approximation. We compare persistent power-law running with a UV-matched tanh weight that saturates at high scalar momentum. Across narrow, finite-width, asymmetric, and multi-slope scalar spectra, running produces more than amplitude renormalization. Power-law running shifts the scalar support sampled by non-Gaussian convolutions, generating peak displacement, asymmetric shoulders, and persistent ultraviolet deformations. The tanh template instead produces a transition-localized modification and approaches a momentum-independent ultraviolet plateau. Analytical estimates of the perturbative hierarchy, weighted slopes, log-normal saddle displacement, peak shifts, and infrared scaling explain the trends and the enhanced sensitivity of the $\mathcal O(\bar f_{\rm NL}^{4})$ sector. For localized sources with finite weighted moments, smooth running preserves the leading $k^3$ infrared behavior up to logarithmic corrections. Since the PBH mass scales as $M\propto k^{-2}$, preferential high-wavenumber weighting conditionally favors lower PBH masses in a narrow-support interpretation. Peak position, spectral curvature, shoulders, and ultraviolet slopes are diagnostics for PTAs, LISA, and third-generation observations, providing finite-order templates for primordial interactions on otherwise inaccessible scales.

astro-ph.CO↗

arXiv2025

Exploring cosmological gravitational wave backgrounds through the synergy of LISA and ET

The gravitational wave (GW) interferometers LISA and ET are expected to be functional in the next decade(s), possibly around the same time. They will operate over different frequency ranges, with similar integrated sensitivities to the amplitude of a stochastic GW background (SGWB). We investigate the synergies between these two detectors, in terms of a multi-band detection of a cosmological SGWB characterised by a large amplitude, and a broad frequency spectrum. We develop the notion of integrated sensitivity and propose a novel signal-to-noise (SNR) optimal for characterization of the geometrical properties of the interferometer systems of LISA and ET operating simultaneously. By investigating various examples of SGWBs, such as those arising from cosmological phase transition, cosmic string, primordial inflation, we show that LISA and ET operating together will have the opportunity to assess more effectively the characteristics of the GW spectrum produced by the same cosmological source, but at separate frequency scales. Moreover, the two experiments in tandem can be sensitive to features of early universe cosmic expansion before big-bang nucleosynthesis (BBN), which affects the SGWB frequency profile, and which would not be possible to detect otherwise, since two different frequency ranges correspond to two different pre-BBN (or post-inflationary) epochs. Besides considering the GW spectrum, we additionally undertake a preliminary study of the sensitivity of LISA and ET to soft limits of higher order tensor correlation functions. Given that these experiments operate at different frequency bands, their synergy constitutes an ideal direct probe of squeezed limits of higher order GW correlators, which can not be measured operating with a single instrument only.

astro-ph.CO↗

arXiv2025

Inflationary magnetogenesis beyond slow-roll and its induced gravitational waves

The origin of magnetic fields observed on both astrophysical and cosmological scales is a compelling problem that has the potential to shed light on the early Universe. We analytically investigate inflationary magnetogenesis in scenarios where a brief departure from slow-roll inflation - akin to mechanisms proposed for primordial black hole formation - leads to enhanced magnetic field generation with a growing power spectrum. Focusing on the Ratra model, we derive an analytic bound on the growth of the magnetic field power spectrum in this context, showing that the spectral index can reach $d \ln {\cal P}_B / d \ln k = 4.75$ during the growth phase. This growth enables amplification from CMB-safe large-scale amplitudes to values of astrophysical relevance. We further compute the stochastic gravitational wave background sourced by the resulting magnetic fields, incorporating their rich spectral features. Under suitable conditions, the induced signal exhibits a characteristic frequency dependence and amplitude within reach of future gravitational wave observatories, providing a distinctive signature of this mechanism and a specific class of templates for upcoming gravitational wave searches.

astro-ph.CO↗

arXiv2025

New gravitational wave probe of vector dark matter

The longitudinal components of massive vector fields generated during inflation constitute a well-motivated dark matter candidate, with interesting phenomenological implications. During the epoch of radiation domination following inflation, their spectrum exhibits a peak at small scales, whose amplitude and position are governed by the parameters of the dark matter model. We calculate the stochastic gravitational wave spectrum induced at second order in fluctuations by such a longitudinal vector peak. We demonstrate that the amplitude of the gravitational wave spectrum can, in principle, reach significant values at nano-Hertz frequencies or lower. This result suggests a novel gravitational wave probe to test inflationary vector dark matter scenarios, independent from assumptions on the coupling of dark vectors to the Standard Model. Additionally, we derive new analytical formulas for the longitudinal vector transfer functions during radiation domination, offering a valuable tool for characterising the convolution integrals that govern the properties of the induced gravitational waves.

astro-ph.CO↗

arXiv2022

Quantum Cosmology of the Nothing

Quantum cosmology uses a wave function to model the universe, but finding solutions for this poses a problem as it is difficult to define the boundary conditions or identify the correct path for a path integral. We begin the discussion by going over various proposals and look at how bubble universe nucleation can be used as an analogy for the tunneling wave function. We review how the Hartle-Hawking wave function and tunneling wave functions are equivalent. This leads into how the transition between the decelerated and accelerated expansion is formulated as a bounce in connection space. This is done in a toy model Universe that contains only radiation and a cosmological constant $Λ$. The wave function is a superposition on an incident wave, a reflected wave, and an evanescent wave; when it is constructed from wave packets. Using the toy model, we introduce the new concept of the universe tunneling to a different classical region during this bounce in connection space. This concept is explored by deriving the wave function of the evanescent wave $ψ_{ev}$ in order to calculate $|ψ|^2$ to give an indication of the probability of the universe tunneling to another classical region.

gr-qc↗