Home | << 1 2 >> |
Aggarwal, N. et al, & Figueroa, D. G. (2021). Challenges and opportunities of gravitational-wave searches at MHz to GHz frequencies. Living Rev. Relativ., 24(1), 4–74pp.
Abstract: The first direct measurement of gravitational waves by the LIGO and Virgo collaborations has opened up new avenues to explore our Universe. This white paper outlines the challenges and gains expected in gravitational-wave searches at frequencies above the LIGO/Virgo band, with a particular focus on Ultra High-Frequency Gravitational Waves (UHF-GWs), covering the MHz to GHz range. The absence of known astrophysical sources in this frequency range provides a unique opportunity to discover physics beyond the Standard Model operating both in the early and late Universe, and we highlight some of the most promising gravitational sources. We review several detector concepts that have been proposed to take up this challenge, and compare their expected sensitivity with the signal strength predicted in various models. This report is the summary of the workshop “Challenges and opportunities of high-frequency gravitational wave detection” held at ICTP Trieste, Italy in October 2019, that set up the stage for the recently launched Ultra-High-Frequency Gravitational Wave (UHF-GW) initiative.
|
Antusch, S., Figueroa, D. G., Marschall, K., & Torrenti, F. (2022). Characterizing the postinflationary reheating history: Single daughter field with quadratic-quadratic interaction. Phys. Rev. D, 105(4), 043532–36pp.
Abstract: We study the evolution of the energy distribution and equation of state of the Universe from the end of inflation until the onset of either radiation domination (RD) or a transient period of matter domination (MD). We use both analytical techniques and lattice simulations. We consider two-field models where the inflaton (/) has a monomial potential after inflation V((/)) proportional to i(/) – vip (p 4, and of order similar to 50% for p 4. The system goes to MD at late times for p = 2, while it goes to RD for p > 2. In the later case, we can calculate exactly the number of e-folds until RD as a function of g2, and hence predict accurately inflationary observables like the scalar tilt ns and the tensor-to-scalar ratio r. In the scenario (ii), the energy is always transferred completely to X for p > 2, as long as its effective mass m2X = g2((/) – v)2 is not negligible. For p = 2, the final ratio between the energy densities of X and (/) depends strongly on g2. For all p > 2, the system always goes to MD at late times.
|
Antusch, S., Figueroa, D. G., Marschall, K., & Torrenti, F. (2020). Energy distribution and equation of state of the early Universe: Matching the end of inflation and the onset of radiation domination. Phys. Lett. B, 811, 135888–7pp.
Abstract: We study the energy distribution and equation of state of the universe between the end of inflation and the onset of radiation domination (RD), considering observationally consistent single-field inflationary scenarios, with a potential 'flattening' at large field values, and a monomial shape V(phi) proportional to vertical bar phi vertical bar(p) around the origin. As a proxy for (p)reheating, we include a quadratic interaction g(2)phi X-2(2) between the inflaton phi and a light scalar 'daughter' field X, with g(2) > 0. We capture the non-perturbative and non-linear nature of the system dynamics with lattice simulations, obtaining that: i) the final energy transferred to X depends only on p, not on g(2); ii) the final transfer of energy is always negligible for 2 <= p < 4, and of order similar to 50% for p >= 4; iii) the system goes at late times to matter-domination for p = 2, and always to RD for p > 2. In the latter case we calculate the number of e-folds until RD, significantly reducing the uncertainty in the inflationary observables Tl-s and r.
|
Auclair, P., Blanco-Pillado, J. J., Figueroa, D. G., Jenkins, A. C., Lewicki, M., Sakellariadou, M., et al. (2020). Probing the gravitational wave background from cosmic strings with LISA. J. Cosmol. Astropart. Phys., 04(4), 034–50pp.
Abstract: Cosmic string networks offer one of the best prospects for detection of cosmological gravitational waves (GWs). The combined incoherent GW emission of a large number of string loops leads to a stochastic GW background (SGWB), which encodes the properties of the string network. In this paper we analyze the ability of the Laser Interferometer Space Antenna (LISA) to measure this background, considering leading models of the string networks. We find that LISA will be able to probe cosmic strings with tensions G μgreater than or similar to O(10(-17)), improving by about 6 orders of magnitude current pulsar timing arrays (PTA) constraints, and potentially 3 orders of magnitude with respect to expected constraints from next generation PTA observatories. We include in our analysis possible modifications of the SGWB spectrum due to different hypotheses regarding cosmic history and the underlying physics of the string network. These include possible modifications in the SGWB spectrum due to changes in the number of relativistic degrees of freedom in the early Universe, the presence of a non-standard equation of state before the onset of radiation domination, or changes to the network dynamics due to a string inter-commutation probability less than unity. In the event of a detection, LISA's frequency band is well-positioned to probe such cosmic events. Our results constitute a thorough exploration of the cosmic string science that will be accessible to LISA.
|
Babak, S., Caprini, C., Figueroa, D. G., Karnesis, N., Marcoccia, P., Nardini, G., et al. (2023). Stochastic gravitational wave background from stellar origin binary black holes in LISA. J. Cosmol. Astropart. Phys., 08(8), 034–37pp.
Abstract: We use the latest constraints on the population of stellar origin binary black holes (SOBBH) from LIGO/Virgo/KAGRA (LVK) observations, to estimate the stochastic gravitational wave background (SGWB) they generate in the frequency band of LISA. In order to account for the faint and distant binaries, which contribute the most to the SGWB, we extend the merger rate at high redshift assuming that it tracks the star formation rate. We adopt different methods to compute the SGWB signal: we perform an analytical evaluation, we use Monte Carlo sums over the SOBBH population realisations, and we account for the role of the detector by simulating LISA data and iteratively removing the resolvable signals until only the confusion noise is left. The last method allows the extraction of both the expected SGWB and the number of resolvable SOBBHs. Since the latter are few for signal-to-noise ratio thresholds larger than five, we confirm that the spectral shape of the SGWB in the LISA band agrees with the analytical prediction of a single power law. We infer the probability distribution of the SGWB amplitude from the LVK GWTC-3 posterior of the binary population model: at the reference frequency of 0.003 Hz it has an interquartile range of h2ΩGW(f = 3 × 10-3 Hz) ∈ [5.65, 11.5] × 10-13, in agreement with most previous estimates. We then perform a MC analysis to assess LISA's capability to detect and characterise this signal. Accounting for both the instrumental noise and the galactic binaries foreground, with four years of data, LISA will be able to detect the SOBBH SGWB with percent accuracy, narrowing down the uncertainty on the amplitude by one order of magnitude with respect to the range of possible amplitudes inferred from the population model. A measurement of this signal by LISA will help to break the degeneracy among some of the population parameters, and provide interesting constraints, in particular on the redshift evolution of the SOBBH merger rate.
|
Cosme, C., Figueroa, D. G., & Loayza, N. (2023). Gravitational wave production from preheating with trilinear interactions. J. Cosmol. Astropart. Phys., 05(5), 023–30pp.
Abstract: We investigate the production of gravitational waves (GWs) during preheating with monomial/polynomial inflationary potentials, considering a trilinear coupling & phi;x2 between a singlet inflaton & phi; and a daughter scalar field x. For sufficiently large couplings, the trilinear interaction leads to an exponential production of x particles and, as a result, a large stochastic GW background (SGWB) is generated throughout the process. We study the linear and non-linear dynamics of preheating with lattice simulations, following the production of GWs through all relevant stages. We find that large couplings lead to SGWBs with amplitudes today that can reach up to h2 �(0) GW <^> 5 & BULL; 10-9. These backgrounds are however peaked at high frequencies fp > 5 & BULL; 106 Hz, which makes them undetectable by current/planned GW observatories. As the amount of GWs produced is in any case remarkable, we discuss the prospects for probing the SGWB indirectly by using constraints on the effective number of relativistic species in the universe Neff.
|
Figueroa, D. G., Florio, A., Loayza, N., & Pieroni, M. (2022). Spectroscopy of particle couplings with gravitational waves. Phys. Rev. D, 106(6), 063522–8pp.
Abstract: We discuss the possibility to measure particle couplings with stochastic gravitational wave backgrounds (SGWBs). Under certain circumstances a sequence of peaks of different amplitude and frequency-a stairway-emerges in a SGWB spectrum, with each peak probing a different coupling. The detection of such signature opens the possibility to reconstruct couplings (spectroscopy) of particle species involved in high energy phenomena generating SGWBs. Stairwaylike signatures may arise in causally produced backgrounds in the early Universe, e.g., from preheating or first order phase transitions. As a proof of principle we study a preheating scenario with an inflaton 0 coupled to multiple daughter fields f chi jg with different coupling strengths. As a clear stairway signature is imprinted in the SGWB spectrum, we reconstruct the relevant couplings with various detectors.
|
Figueroa, D. G., Florio, A., Opferkuch, T., & Stefanek, B. (2023). Lattice simulations of non-minimally coupled scalar fields in the Jordan frame. SciPost Phys., 15(3), 077–28pp.
Abstract: The presence of scalar fields with non-minimal gravitational interactions of the form & xi;|& phi;|2R may have important implications for the physics of the early universe. We propose a procedure to solve the dynamics of non-minimally coupled scalar fields directly in the Jordan frame, where the non-minimal couplings are maintained explicitly. Our algorithm can be applied to lattice simulations that include minimally coupled fields and an arbitrary number of non-minimally coupled scalars, with the expansion of the universe sourced by all fields present. This includes situations when the dynamics become fully inhomogeneous, fully non-linear (due to e.g. backreaction or mode rescattering effects), and/or when the expansion of the universe is dominated by non-minimally coupled species. As an example, we study geometric preheating with a non-minimally coupled scalar spectator field when the inflaton oscillates following the end of inflation.
|
Figueroa, D. G., Florio, A., Torrenti, F., & Valkenburg, W. (2023). CosmoLattice: A modern code for lattice simulations of scalar and gauge field dynamics in an expanding universe. Comput. Phys. Commun., 283, 108586–13pp.
Abstract: This paper describes CosmoGattice, a modern package for lattice simulations of the dynamics of interacting scalar and gauge fields in an expanding universe. CosmoGattice incorporates a series of features that makes it very versatile and powerful: i) it is written in C++ fully exploiting the object oriented programming paradigm, with a modular structure and a clear separation between the physics and the technical details, ii) it is MPI-based and uses a discrete Fourier transform parallelized in multiple spatial dimensions, which makes it specially appropriate for probing scenarios with well -separated scales, running very high resolution simulations, or simply very long ones, iii) it introduces its own symbolic language, defining field variables and operations over them, so that one can introduce differential equations and operators in a manner as close as possible to the continuum, iv) it includes a library of numerical algorithms, ranging from O(delta t(2)) to O(delta t(10)) methods, suitable for simulating global and gauge theories in an expanding grid, including the case of 'self-consistent' expansion sourced by the fields themselves. Relevant observables are provided for each algorithm (e.g. energy densities, field spectra, lattice snapshots) and we note that, remarkably, all our algorithms for gauge theories (Abelian or non-Abelian) always respect the Gauss constraint to machine precision. Program summary Program Title:: CosmoGattice CPC Library link to program files: https://doi .org /10 .17632 /44vr5xssc6 .1 Developer's repository link: http://github .com /cosmolattice /cosmolattice Licensing provisions: MIT Programming language: C++, MPI Nature of problem: The phenomenology of high energy physics in the early universe is typically characterized by non-linear dynamics, which cannot be captured accurately with analytical techniques. In order to fully understand the non-linearities developed in a given scenario, one needs to carry out lattice simulations. A number of public packages for lattice simulations have appeared over the years, but most of them are only capable of simulating scalar fields. However, realistic models of particle physics do contain other kind of field species, such as (Abelian or non-Abelian) gauge fields, whose non-linear dynamics can also play a relevant role in the early universe. Tensor modes representing gravitational waves are also naturally expected in many scenarios. Solution method: CosmoGattice represents a modern code for lattice simulations of scalar-gauge field theories in an expanding universe. It allows for the simulation of the evolution of interacting (singlet) scalar fields, charged scalar fields under U(1) and/or SU(2) gauge groups, and the corresponding associated Abelian and/or non-Abelian gauge fields. From version 1.1 onward, CosmoGattice also allows to simulate the production of gravitational waves. Simulations can be done either in a flat space-time background, or in a homogeneous and isotropic (spatially flat) expanding FLRW background. CosmoGattice provides symplectic integrators, with accuracy ranging from O (delta t(2)) up to O(delta t(10)), to simuate the non-linear dynamics of the appropriate fields in comoving three-dimensional lattices. The code is parallelized with MPI, and uses a discrete Fourier Transform parallelized in multiple spatial dimensions, which makes it a very powerful code for probing physical problems with well-separated scales. Moreover, the code has been designed as a `platform' to implement any system of dynamical equations suitable for discretization on a lattice.
|
Figueroa, D. G., Florio, A., Torrenti, F., & Valkenburg, W. (2021). The art of simulating the early universe. Part I. Integration techniques and canonical cases. J. Cosmol. Astropart. Phys., 04(4), 035–108pp.
Abstract: We present a comprehensive discussion on lattice techniques for the simulation of scalar and gauge field dynamics in an expanding universe. After reviewing the continuum formulation of scalar and gauge field interactions in Minkowski and FLRW backgrounds, we introduce the basic tools for the discretization of field theories, including lattice gauge invariant techniques. Following, we discuss and classify numerical algorithms, ranging from methods of O(delta t(2)) accuracy like staggered leapfrog and Verlet integration, to Runge-Kutta methods up to O(delta t(4)) accuracy, and the Yoshida and Gauss-Legendre higher-order integrators, accurate up to O(delta t(10)) We adapt these methods for their use in classical lattice simulations of the non-linear dynamics of scalar and gauge fields in an expanding grid in 3+1 dimensions, including the case of 'self-consistent' expansion sourced by the volume average of the fields' energy and pressure densities. We present lattice formulations of canonical cases of: i) Interacting scalar fields, ii) Abelian U(1) gauge theories, and iii) Non-Abelian SU(2) gauge theories. In all three cases we provide symplectic integrators, with accuracy ranging from O(delta t(2)) up to O(delta t(10)) For each algorithm we provide the form of relevant observables, such as energy density components, field spectra and the Hubble constraint. We note that all our algorithms for gauge theories always respect the Gauss constraint to machine precision, including when 'self-consistent' expansion is considered. As a numerical example we analyze the post-inflationary dynamics of an oscillating inflaton charged under SU(2) x U(1). We note that the present manuscript is meant to be part of the theoretical basis for the code CosmoLattice, a multi-purpose MPI-based package for simulating the non-linear evolution of field theories in an expanding universe, publicly available at http://www.cosrnolattice.net.
|