Detection of Early-Universe Gravitational Wave Signatures and Fundamental Physics (original) (raw)
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Signatures of Primordial Gravitational Waves on the Large-Scale Structure of the Universe
Physical Review Letters
We study the generation and evolution of second-order energy-density perturbations arising from primordial gravitational waves. Such "tensor-induced scalar modes" approximately evolve as standard linear matter perturbations and may leave observable signatures in the Large-Scale Structure of the Universe. We study the imprint on the matter power spectrum of some primordial models which predict a large gravitational-wave signal at high frequencies. This novel mechanism in principle allows us to constrain or detect primordial gravitational waves by looking at specific features in the matter or galaxy power spectrum and allows us to probe them on a range of scales which are unexplored so far.
Detectability of the primordial origin of the gravitational wave background in the Universe
1999
The appearance of peaks in various primordial fluctuation Fourier power spectra is a generic prediction of the inflationary scenario. We investigate whether future experiments, in particular the satellite experiment PLANCK, will be able to detect the possible appearance of these peaks in the B-mode polarization multipole power spectrum. This would yield a conclusive proof of the presence of a primordial background of gravitational waves.
Constraining inflation through joint observations of the primordial gravitational wave background
2016
The standard cosmological model leaves many questions unanswered. An early period of accelerated expansion of the Universe, referred to as inflation, resolves these issues. It provides a means to generate perturbations in matter and density that lead to the formation of structure as well as in gravitational waves. Inflation preserves fluctuations by driving them beyond the causal horizon. Their wavelengths trace the time they exit and their amplitude reveals the expansion rate and inflationary potential energy at exit. Measurements of these fluctuations is therefore a powerful probe of the inflationary Universe. After providing the necessary overview of background cosmology and inflation, I explore our ability to constrain viable models using joint measurements at vastly separated length scales and frequencies. Particular attention is paid to observations of the tensor power spectrum at large scales through measurements of the B-mode polarization of the cosmic microwave background a...
Primordial gravitational waves and cosmology
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The observation of primordial gravitational waves could provide a new and unique window on the earliest moments in the history of the universe, and on possible new physics at energies many orders of magnitude beyond those accessible at particle accelerators. Such waves might be detectable soon in current or planned satellite experiments that will probe for characteristic imprints in the polarization of the cosmic microwave background (CMB), or later with direct space-based interferometers. A positive detection could provide definitive evidence for Inflation in the early universe, and would constrain new physics from the Grand Unification scale to the Planck scale.
Physical Review D, 2021
In all inflationary scenarios of primordial black holes (PBH) formation, amplified scalar perturbations inevitably accompany an induced stochastic gravitational waves background (ISGWB) at smaller scales. In this paper, we study the ISGWB originating from the inflationary model, introduced in our previous paper [1] wherein PBHs can be produced with a nearly monochromatic mass fraction in the asteroid mass window accounting for the total dark matter in the universe. We numerically calculate the ISGWB in our scenario for frequencies ranging from nanoHz to KHz that covers the observational scales corresponding to future space based GW observatories such as IPTA, LISA, DECIGO and ET. Interestingly, we find that ultralight PBHs (M PBH ∼ 10 −20 M) which shall completely evaporate by today with exceedingly small contribution to dark matter, would still generate an ISGWB that may be detected by a future design of the ground based Advanced LIGO detector. Using a model independent approach, we obtain a stringent lower mass limit for ultralight PBHs which would be valid for a large class of ultra slow roll inflationary models. Further, we extend our formalism to study the imprints of a reheating epoch on both the ISGWB and the derived lower mass bound. We find that any non-instantaneous reheating leads to an even stronger lower bound on PBHs mass and an epoch of a prolonged matter dominated reheating shifts the ISGWB spectrum to smaller frequencies. In particular, we show that an epoch of an early matter dominated phase leads to a secondary amplification of ISGWB at much smaller scales corresponding to the smallest comoving scale leaving the horizon during inflation or the end of inflation scale. Finally, we discuss the prospects of the ISGWB detection by the proposed and upcoming GW observatories.
Probing Fundamental Physics with Gravitational Waves
arXiv: General Relativity and Quantum Cosmology, 2020
The explosive coalescence of two black holes 1.3 billion light years away has for the very first time allowed us to peer into the extreme gravity region of spacetime surrounding these events. With these maximally compact objects reaching speeds up to 60% the speed of light, collision events such as these create harsh spacetime environments where the fields are strong, non-linear, and highly dynamical -- a place yet un-probed in human history. On September 14, 2015, the iconic chirp signal from such an event was registered simultaneously by both of the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors -- by an unparalleled feat of modern engineering. Dubbed "GW150914", this gravitational wave event paved the way for an entirely new observing window into the universe, providing for the unique opportunity to probe fundamental physics from an entirely new viewpoint. Since this historic event, the LIGO/Virgo collaboration (LVC) has further identified ten addi...
Relic High Frequency Gravitational waves from the Big Bang and How to Detect Them
AIP Conference Proceedings, 2009
This paper shows how entropy generation from numerical density calculations of relic gravitons can be measured via the Li-Baker high-frequency gravity wave (HFGW) detector, and suggests the implications this has for the physics of early-universe phase transitions. This paper indicates the role of Ng's revised statistics in gravitational wave physics detection and the application of Baumann et al. (2007) formalism of reduction of rank-two tensorial contributions to density wave physics, using the HFGW approximation directly at the beginning as well as Li's treatment of energy density explicitly. This formalism is a way to refine and add more capacity to the Li-Baker HFGW detector in reconstructing early-universe conditions at the onset of the big bang. Furthermore, we bring up how the HFGW detector can have its data sets compared and swapped with ice cube relic neutrino physics data taken at the south pole. This will enable us to begin to get criteria to falsify different inflation models as alluded to at the end of this manuscript.
2022
The imprint of gravitational waves (GWs) on large-scale structures (LSS) is a useful and promising way to detect or to constrain them. Tensor fossils have been largely studied in the literature as an indirect way to detect primordial GWs. In this paper we analyze a new effect induced by primordial GWs: a correction to the density contrast of the underlying matter distribution of LSS, as well as its radiation counterpart, induced by the energy density fluctuation of the gravitational radiation. We perform our derivation of the full analytical solution of the density contrast for waves entering the horizon during radiation dominance. We account for two phases in the radiation era, depending on the main contributor to the perturbed energy density of the Universe. By comparing the density contrast of cold dark matter and radiation-sourced by linear gravitational waves only-we conclude that the former overcomes the latter at some time in the radiation era, a behaviour analogous to their linear counterpart. Then we conclude by discussing the case of density perturbations produced by GWs entering the Hubble radius during the matter era as well as their evolution in the late dark-energy dominated phase. Appendix B General solution during deep radiation dominance, without subhorizon approximation 34 Appendix C Calculation of δ r in the second phase 36 Appendix D Setup of the initial conditions 42
Primordial gravitational wave signals in modified cosmologies
Journal of Cosmology and Astroparticle Physics, 2020
Modified expansion rates in the early Universe prior to big bang nucleosynthesis are common in modified gravity theories, and can have a significant impact on the generation of dark matter, matter-antimatter asymmetry, primordial black holes and the primordial gravitational wave (PGW) spectrum. Here we study the PGW spectrum in modified gravity theories, in early Universe cosmology. In particular, we consider scalar-tensor and extradimensional scenarios, investigating the detection prospects in current and future GW observatories. For the scalar-tensor case, PGW could be potentially observed by laser interferometers operating in the high-frequency range, while for the extradimensional case they could be detected even at low frequencies with pulsar timing arrays. We find that data from the planned network of several GW detectors operating across various frequency ranges could be able to distinguish between various modified gravity scenarios.