16 research outputs found
Constraining primordial tensor features with the anisotropies of the Cosmic Microwave Background
It is commonly assumed that the stochastic background of gravitational waves
on cosmological scales follows an almost scale-independent power spectrum, as
generically predicted by the inflationary paradigm. However, it is not
inconceivable that the spectrum could have strongly scale-dependent features,
generated, e.g., via transient dynamics of spectator axion-gauge fields during
inflation. Using the temperature and polarisation maps from the \textit{Planck}
and BICEP/Keck datasets, we search for such features, taking the example of a
log-normal bump in the primordial tensor spectrum at CMB scales. We do not find
any evidence for the existence of bump-like tensor features at present, but
demonstrate that future CMB experiments such as LiteBIRD and CMB-S4 will
greatly improve our prospects of determining the amplitude, location and width
of such a bump. We also highlight the role of delensing in constraining these
features at angular scales .Comment: 16 pages, 7 figure
Probing Inflationary Physics with Gravitational Waves
Cosmological observables beyond the two-point function of density perturbations may hold the key to answering fundamental questions about inflation. One such observable is the inflationary gravitational wave (GW) background, expected to arise in all models of inflation. A detection of this GW background may reveal to us the energy scale of inflation and even point us towards the fields and interactions present during the inflationary epoch. In this thesis, I explore the GW signatures of inflationary models beyond the simple single-field scenarios, focusing on their anisotropies, non-Gaussianity and spectral shape.
For the anisotropies, I first study GW backgrounds with a sharply peaked spectral shapes, which can arise in inflationary scenarios involving primordial black hole formation and discuss the implications of this spectral shape for the detection of the anisotropies. I then derive general results for cosmological gravitational wave background anisotropies arising from adiabatic initial conditions. I also discuss the impact of isocurvature initial conditions through the representative example of the curvaton mechanism and show how GW anisotropies and their cross-correlations with the CMB provide an alternative handle on the curvaton dynamics.
On the subject on non-Gaussianity, I show how a sizeable squeezed limit tensor bispectrum can generate large GW anisotropies. Although the direct measurement of tensor non-Gaussianity is not possible at interferometer scales, this method still provides an indirect way to observe tensor non-Gaussianity with interferometers. I then discuss the prospects of doing ``cosmological collider physics'' with such GW anisotropies, showing that the correlators of these anisotropies are particularly sensitive to the spin of additional fields that source the GW.
Finally, I turn to the GW spectral shape, focusing on large scale observations through the temperature and polarisation anisotropies of the CMB. Using current CMB data, I test for GW signatures of axion-gauge field models which typically produce a bump like spectral shape and demonstrate the detectability of such signatures with future experiments such as LiteBIRD and CMB-S4
Measuring kinematic anisotropies with pulsar timing arrays
Recent pulsar timing array (PTA) collaborations show strong evidence for a stochastic gravitational wave background (SGWB) with the characteristic Hellings-Downs interpulsar correlations. The signal may stem from supermassive black hole binary mergers, or early Universe phenomena. The former is expected to be strongly anisotropic, while primordial backgrounds are likely to be predominantly isotropic with small fluctuations. In the case the observed SGWB is of cosmological origin, our relative motion with respect to the SGWB rest frame is a guaranteed source of anisotropy, leading to (10−3) energy density fluctuations of the SGWB. For such cosmological SGWB, kinematic anisotropies are likely to be larger than the intrinsic anisotropies, akin to the cosmic microwave background (CMB) dipole anisotropy. We assess the sensitivity of current PTA data to the kinematic dipole anisotropy, and we also forecast at what extent the magnitude and direction of the kinematic dipole can be measured in the future with an SKA-like experiment. We also discuss how the spectral shape of the SGWB and the location of the pulsars to monitor affect the prospects of detecting the kinematic dipole with PTA. In the future, a detection of this anisotropy may even help resolve the discrepancy in the magnitude of the kinematic dipole as measured by CMB and large-scale structure observations
Testing the early universe with anisotropies of the gravitational wave background
In this work we analyse in detail the possibility of using small and
intermediate-scale gravitational wave anisotropies to constrain the
inflationary particle content. First, we develop a phenomenological approach
focusing on anisotropies generated by primordial tensor-tensor-scalar and
purely gravitational non-Gaussianities. We highlight the quantities that play a
key role in determining the detectability of the signal. To amplify the power
of anisotropies as a probe of early universe physics, we consider
cross-correlations with CMB temperature anisotropies. We assess the size of the
signal from inflationary interactions against so-called induced anisotropies.
In order to arrive at realistic estimates, we obtain the projected constraints
on the non-linear primordial parameter for several upcoming
gravitational wave probes in the presence of the astrophysical gravitational
wave background. We further illustrate our findings by considering a concrete
inflationary realisation and use it to underscore a few subtleties in the
phenomenological analysis.Comment: 47 pages, 16 figure
Cosmology with the Laser Interferometer Space Antenna
254 pags:, 44 figs.The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate of the universe, and to understand stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational-wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational-wave observations by LISA to probe the universe.This work is partly supported by: A.G. Leventis Foundation; Academy of Finland
Grants 328958 and 345070; Alexander S. Onassis Foundation, Scholarship ID: FZO 059-1/2018-2019;
Amaldi Research Center funded by the MIUR program “Dipartimento di Eccellenza” (CUP:
B81I18001170001); ASI Grants No. 2016-24-H.0 and No. 2016-24-H.1-2018; Atracción de Talento
Grant 2019-T1/TIC-15784; Atracción de Talento contract no. 2019-T1/TIC-13177 granted by the
Comunidad de Madrid; Ayuda ‘Beatriz Galindo Senior’ by the Spanish ‘Ministerio de Universidades’,
Grant BG20/00228; Basque Government Grant (IT-979-16); Belgian Francqui Foundation; Centre national
d’Etudes spatiales; Ben Gurion University Kreitman Fellowship, and the Israel Academy of Sciences and
Humanities (IASH) & Council for Higher Education (CHE) Excellence Fellowship Program for
International Postdoctoral Researchers; Centro de Excelencia Severo Ochoa Program SEV-2016-0597;
CERCA program of the Generalitat de Catalunya; Cluster of Excellence “Precision Physics, Fundamental
Interactions, and Structure of Matter” (PRISMA? EXC 2118/1); Comunidad de Madrid, Contrato de
Atracción de Talento 2017-T1/TIC-5520; Czech Science Foundation GAČR, Grant No. 21-16583M; Delta
ITP consortium; Department of Energy under Grant No. DE-SC0008541, DE-SC0009919 and DESC0019195; Deutsche Forschungsgemeinschaft (DFG), Project ID 438947057; Deutsche Forschungsgemeinschaft under Germany’s Excellence Strategy - EXC 2121 Quantum Universe - 390833306; European
Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project
CoGraDS - CZ.02.1.01/0.0/0.0/15 003/0000437); European Union’s H2020 ERC Consolidator Grant
“GRavity from Astrophysical to Microscopic Scales” (Grant No. GRAMS-815673); European Union’s
H2020 ERC, Starting Grant Agreement No. DarkGRA-757480; European Union’s Horizon 2020
programme under the Marie Sklodowska-Curie Grant Agreement 860881 (ITN HIDDeN); European
Union’s Horizon 2020 Research and Innovation Programme Grant No. 796961, “AxiBAU” (K.S.);
European Union’s Horizon 2020 Research Council grant 724659 MassiveCosmo ERC-2016-COG; FCT
through national funds (PTDC/FIS-PAR/31938/2017) and through project “BEYLA – BEYond LAmbda”
with Ref. Number PTDC/FIS-AST/0054/2021; FEDER-Fundo Europeu de Desenvolvimento Regional
through COMPETE2020 - Programa Operacional Competitividade e Internacionalização (POCI-01-0145-
FEDER-031938) and research Grants UIDB/04434/2020 and UIDP/04434/2020; Fondation CFM pour la
Recherche in France; Foundation for Education and European Culture in Greece; French ANR project
MMUniverse (ANR-19-CE31-0020); FRIA Grant No.1.E.070.19F of the Belgian Fund for Research, F.R.
S.-FNRS Fundação para a Ciência e a Tecnologia (FCT) through Contract No. DL 57/2016/CP1364/
CT0001; Fundação para a Ciência e a Tecnologia (FCT) through Grants UIDB/04434/2020, UIDP/04434/
2020, PTDC/FIS-OUT/29048/2017, CERN/FIS-PAR/0037/2019 and “CosmoTests – Cosmological tests of
gravity theories beyond General Relativity” CEECIND/00017/2018; Generalitat Valenciana Grant
PROMETEO/2021/083; Grant No. 758792, project GEODESI; Government of Canada through the
Department of Innovation, Science and Economic Development and Province of Ontario through the
Ministry of Colleges and Universities; Grants-in-Aid for JSPS Overseas Research Fellow (No.
201960698); I?D Grant PID2020-118159GB-C41 of the Spanish Ministry of Science and Innovation;
INFN iniziativa specifica TEONGRAV; Israel Science Foundation (Grant No. 2562/20); Japan Society for
the Promotion of Science (JSPS) KAKENHI Grant Nos. 20H01899 and 20H05853; IFT Centro de
Excelencia Severo Ochoa Grant SEV-2; Kavli Foundation and its founder Fred Kavli; Minerva
Foundation; Ministerio de Ciencia e Innovacion Grant PID2020-113644GB-I00; NASA Grant
80NSSC19K0318; NASA Hubble Fellowship grants No. HST-HF2-51452.001-A awarded by the Space
Telescope Science Institute with NASA contract NAS5-26555; Netherlands Organisation for Science and
Research (NWO) Grant Number 680-91-119; new faculty seed start-up grant of the Indian Institute of
Science, Bangalore, the Core Research Grant CRG/2018/002200 of the Science and Engineering; NSF
Grants PHY-1820675, PHY-2006645 and PHY-2011997; Polish National Science Center Grant 2018/31/D/
ST2/02048; Polish National Agency for Academic Exchange within the Polish Returns Programme under
Agreement PPN/PPO/2020/1/00013/U/00001; Pró-Reitoria de Pesquisa of Universidade Federal de Minas
Gerais (UFMG) under Grant No. 28359; Ramón y Cajal Fellowship contract RYC-2017-23493; Research
Project PGC2018-094773-B-C32 [MINECO-FEDER]; Research Project PGC2018-094773-B-C32
[MINECO-FEDER]; ROMFORSK Grant Project. No. 302640; Royal Society Grant URF/R1/180009
and ERC StG 949572: SHADE; Shota Rustaveli National Science Foundation (SRNSF) of Georgia (Grant
FR/18-1462); Simons Foundation/SFARI 560536; SNSF Ambizione grant; SNSF professorship Grant
(No. 170547); Spanish MINECO’s “Centro de Excelencia Severo Ochoa” Programme Grants SEV-2016-
0597 and PID2019-110058GB-C22; Spanish Ministry MCIU/AEI/FEDER Grant (PGC2018-094626-BC21); Spanish Ministry of Science and Innovation (PID2020-115845GB-I00/AEI/10.13039/
501100011033); Spanish Proyectos de I?D via Grant PGC2018-096646-A-I00; STFC Consolidated
Grant ST/T000732/1; STFC Consolidated Grants ST/P000762/1 and ST/T000791/1; STFC Grant ST/
S000550/1; STFC Grant ST/T000813/1; STFC Grants ST/P000762/1 and ST/T000791/1; STFC under the
research Grant ST/P000258/1; Swiss National Science Foundation (SNSF), project The Non-Gaussian
Universe and Cosmological Symmetries, Project Number: 200020-178787; Swiss National Science
Foundation Professorship Grants No. 170547 and No. 191957; SwissMap National Center for Competence
in Research; “The Dark Universe: A Synergic Multi-messenger Approach” Number 2017X7X85K under
the MIUR program PRIN 2017; UK Space Agency; UKSA Flagship Project, Euclid.Peer reviewe
Third EuCAPT Annual Symposium
The anisotropies of the stochastic gravitational wave background, as produced in the early phases of cosmological evolution, can act as a key probe of the primordial universe particle content. We point out a universal property of gravitational wave anisotropies of cosmological origin: for adiabatic initial conditions, their angular power spectrum is insensitive to the equation of state of the cosmic fluid driving the expansion before BBN. Any deviation from this universal behaviour points to the presence of non-adiabatic sources of primordial fluctuations. In this work we prove this general result, and we illustrate its consequences for a representative realisation of initial conditions based on the curvaton scenario. In the case of the simplest curvaton setup, we also find a fourfould enhancement in the cross-correlation between gravitational wave anisotropies and the CMB temperature fluctuations, vis-à-vis the purely adiabatic scenario
Enhancing gravitational wave anisotropies with peaked scalar sources
Gravitational wave (GW) backgrounds of cosmological origin are expected to be
nearly isotropic, with small anisotropies resembling those of the cosmic
microwave background. We analyse the case of a scalar-induced GW background and
clarify in the process the relation between two different approaches to
calculating GW anisotropies. We focus on GW scenarios sourced by a
significantly peaked scalar spectrum, which are frequently considered in the
context of primordial black holes production. We show that the resulting GW
anisotropies are characterised by a distinct frequency dependence. We explore
the observational consequences concentrating on a GW background enhanced in the
frequency band of space-based GW detectors. We study the detectability of the
signal through both cross-correlations among different space-based GW
detectors, and among GW and CMB experiments.Comment: 28 pages, 6 figure
Enhancing gravitational wave anisotropies with peaked scalar sources
Gravitational wave (GW) backgrounds of cosmological origin are expected to be nearly isotropic, with small anisotropies resembling those of the cosmic microwave background. We analyse the case of a scalar-induced GW background and clarify in the process the relation between two different approaches to calculating GW anisotropies. We focus on GW scenarios sourced by a significantly peaked scalar spectrum, which are frequently considered in the context of primordial black holes production. We show that the resulting GW anisotropies are characterised by a distinct frequency dependence. We explore the observational consequences concentrating on a GW background enhanced in the frequency band of space-based GW detectors. We study the detectability of the signal through both cross-correlations among different space-based GW detectors, and among GW and CMB experiments