Papers by Ivan de Martino
Phys. Rev. D 110, 083519 , 2024
We have probed the capability of third-generation Gravitational Waves (GW) interferometers, such ... more We have probed the capability of third-generation Gravitational Waves (GW) interferometers, such as the Einstein Telescope and Cosmic Explorer, to constrain a cosmological model with an interacting dark sector. We focused on GW events with a detected electromagnetic counterpart being the γ or X emission of Gamma-Ray Burst, and a Kilonova emission. We assume the first one to be detected by the THESEUS satellite, while the second one to be detected by the Vera Rubin Observatory. We probed three different interaction kernels and found that the posterior estimation of the cosmological parameters is biased due to the existing degeneracies between the dark and matter sectors. We also found that introducing an external prior on the matter density parameter breaks the degeneracy, removes the bias results, and improves the accuracy on the dark sector parameters.
Physical Review D, Volume 109, Issue 2, article id.024016, 2024
We consider a static, spherically symmetric space-time with an electric field arising from a quad... more We consider a static, spherically symmetric space-time with an electric field arising from a quadratic metric-affine extension of General Relativity. Such a space-time is free of singularities in the centre of the black holes, while at large distances it quickly boils down to the usual Reissner-Nordström solution. We probe this space-time metric, which is uniquely characterized by two length scales, rq and ℓ, using the astrometric and spectroscopic measurements of the orbital motion of the S2 star around the Galactic Center. Our analysis constrains rq to be below 2.7M for values ℓ < 120AU , strongly favouring a central object that resembles a Schwarzschild black hole.
We investigate whether the oblate, spheroidal morphology of common dwarf spheroidal galaxies (dSp... more We investigate whether the oblate, spheroidal morphology of common dwarf spheroidal galaxies (dSph) may result from the slow relaxation of stellar orbits within a halo of wave dark matter (ψDM) when starting from an initial disc of stars. Stellar orbits randomly walk o v er a Hubble time, perturbed by the perv asi ve 'granular' interference pattern of ψDM, that fully modulates the dark matter density on the de Broglie scale. Our simulations quantify the level of stellar disc thickening over the Hubble time, showing that distribution of stars is predicted to become an oblate spheroid of increasing radius, that plausibly accounts for the morphology of dSph galaxies. We predict a low level of residual rotation remains after a Hubble time at the 1-3 km/s level, depending on orientation, that compares with recent claims of rotation for some well-studied local dSph galaxies. This steady internal dynamical evolution may be witnessed directly with JWST for well-resolved dwarf galaxies, appearing more oblate with look back time and tending to small discs of young stars at high redshift.
A&A 670, L4, 2023
Aims. It is well known that N-body simulations of ultralight bosons display the formation of a so... more Aims. It is well known that N-body simulations of ultralight bosons display the formation of a solitonic dark matter core in the innermost part of the halo. The scale-length of such a soliton depends on the inverse of the mass of the boson. On the other hand, the orbital motion of stars in the Galactic Center depends on the distribution of matter, no matter whether it is baryonic or dark, providing an excellent probe for the gravitational field of the region. In this Letter, we propose the S-stars in the Galactic Center as a new observational tool, complementary to other astrophysical systems, to narrow down the range of allowed values for an ultralight dark matter candidate boson mass. Methods. We built mock catalogs mirroring the forthcoming astrometric and spectroscopic observations of S2 and we used a MCMC analysis to predict the accuracy down to which the mass of an ultralight boson may be bounded. We show that once complementary constraints are considered, this analysis will help to restrict the allowed range of the boson mass. Results. Our analysis forecasts the boundary limit on the mass of an ultralight boson to be <10 −19 eV at a 95% confidence level.
Phys Rev D, 107, 044038, 2023
We investigate a nonsingular black hole spacetime representing a strong deformation of the Schwar... more We investigate a nonsingular black hole spacetime representing a strong deformation of the Schwarzschild solution with mass M by an additional hair l, which may be hierarchically larger than the Planck scale. The spacetime is an exact solution of Einstein's equations sourced by an anisotropic fluid. The model presents a de Sitter core and Oðl 2 =r 2 Þ slow-decaying corrections to the Schwarzschild solution. These solutions are thermodynamically preferred when 0.2 ≲ l=GM ≲ 0.3 and are characterized by strong deviations in the orbits of test particles from the Schwarzschild case. In particular, we find corrections to the perihelion precession angle scaling linearly with l. We test our model using the available data for the orbits of the S2 star around SgrA Ã. These data strongly constrain the value of the hair l, casting an upper bound on it of ∼0.47GM but do not rule out the possible existence of regular black holes with super-Planckian hair.
MNRAS 519, 4424-4433 , 2023
We use the kinematic data of the stars in eight dwarf spheroidal galaxies to assess whether f (R)... more We use the kinematic data of the stars in eight dwarf spheroidal galaxies to assess whether f (R) gravity can fit the observed profiles of the line-of-sight velocity dispersion of these systems without resorting to dark matter. Our model assumes that each galaxy is spherically symmetric and has a constant velocity anisotropy parameter β and constant mass-to-light ratio consistent with stellar population synthesis models. We solve the spherical Jeans equation that includes the Yukaw a-lik e gravitational potential appearing in the weak field limit of f (R) gravity, and a Plummer density profile for the stellar distribution. The f (R) velocity dispersion profiles depends on two parameters: the scale length ξ −1 , below which the Yukawa term is negligible, and the boost of the gravitational field δ > −1. δ and ξ are not universal parameters, but their variation within the same class of objects is expected to be limited. The f (R) velocity dispersion profiles fit the data with a value ξ −1 = 1. 2 + 18. 6 −0. 9 Mpc for the entire galaxy sample. On the contrary, the values of δ show a bimodal distribution that picks at δ = −0. 986 ± 0. 002 and δ = −0. 92 ± 0. 01. These two values disagree at 6 σ and suggest a severe tension for f (R) gravity. It remains to be seen whether an impro v ed model of the dwarf galaxies or additional constraints provided by the proper motions of stars measured by future astrometric space missions can return consistent δ's for the entire sample and remo v e this tension.
MNRAS 519, 1981–1988 , 2023
We have explored a completely new and alternative way to restrict the parameter space of Horndesk... more We have explored a completely new and alternative way to restrict the parameter space of Horndeski theory of gravity. Using its Newtonian limit, it is possible to test the theory at a regime where, given its complexity and the small magnitude of the expected effects, it is poorly probed. At Newtonian level, it gives rise to a generalized Yukaw a-lik e Newtonian potential which we have tested using S2 star orbit data. Our model adds five parameters to the General Relativity model, and the analysis constrains two of them with unprecedented precision to these energy scales, while it only gives an e xclusion re gion for the remaining parameters. We have shown the potential of weak-field tests to constrain Horndeski gravity opening, as a matter of fact, which is a new avenue that deserves to be further, and deeply, explored in the near future.
MNRAS 518, 3372–3385, 2023
We investigate the capability of Einstein Telescope to constrain the cosmological parameters of t... more We investigate the capability of Einstein Telescope to constrain the cosmological parameters of the non-flat CDM cosmological model. Two types of mock data sets are considered depending on whether or not a short gamma-ray burst is detected, and associated with the gravitational wave emitted by binary neutron stars merger, using the THESEUS satellite. Depending on the mock data set, two statistical estimators are applied: one assumes that the redshift is known, while the other marginalizes o v er it assuming a specific redshift prior distribution. We demonstrate that (i) using mock catalogues collecting gravitational wave signals emitted by binary neutron stars systems to which a short gamma-ray burst has been associated, Einstein Telescope may achieve an accuracy on the cosmological parameters of σ H 0 ≈ 0. 40 km s −1 Mpc −1 , σ k, 0 ≈ 0. 09, and σ , 0 ≈ 0. 07; while (ii) using mock catalogues collecting all gra vitational wa ve signals emitted by binary neutron stars systems for which an electromagnetic counterpart has not been detected, Einstein Telescope may achieve an accuracy on the cosmological parameters of σ H 0 ≈ 0. 04 km s −1 Mpc −1 , σ k, 0 ≈ 0. 01, and σ , 0 ≈ 0. 01, once the redshift probability distribution of GW events is known from from population synthesis simulations and/or the measure of the tidal deformability parameter. These results show an impro v ement of a factor 2-75 with respect to earlier results using complementary data sets.
MNRAS 516, 3556–3568 (2022) , 2022
We show that measuring the proper motion of ∼2000 stars within a dwarf galaxy, with an uncertaint... more We show that measuring the proper motion of ∼2000 stars within a dwarf galaxy, with an uncertainty of 1 km s −1 at most, can establish whether the dark matter (DM) density profile of the dwarf has a central core or cusp. We derive these limits by building mock star catalogues similar to those expected from future astrometric Theia-like missions and including celestial coordinates, radial velocity and proper motion of the stars. The density field of the DM halo of the dwarf is sampled from an extended Navarro-Frank-White (eNFW) spherical model, whereas the number density distribution of the stars is a Plummer sphere. The velocity field of the stars is set according to the Jeans equations. A Monte Carlo Markov chain algorithm applied to a sample of N 2000 stars returns unbiased estimates of the eNFW DM parameters within 10 per cent of the true values and with 1 σ relative uncertainties ࣠ 20 per cent. The proper motions of the stars lift the de generac y among the eNFW parameters which appears when the line-of-sight velocities alone are available. Our analysis demonstrates that, by estimating the log-slope of the mass density profile estimated at the half-light radius, a sample of N = 2000 stars can distinguish between a core and a cusp at more than 8 σ. Proper motions also return unbiased estimates of the dwarf mass profile with 1 σ uncertainties that decrease, on average, from 2.65 dex to 0.15 dex when the size of the star sample increases from N = 100 to N = 6000 stars. The measure of the proper motions can thus strongly constrain the distribution of DM in nearby dwarfs and provides fundamental contribution to understanding the nature and the properties of DM.
Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 4, pp.4757-4766, 2022
We have obtained the first constraint of the parameter space of Scalar-Tensor-Vector-Gravity usin... more We have obtained the first constraint of the parameter space of Scalar-Tensor-Vector-Gravity using the motion of the S2-star around the supermassive black hole at the centre of the Milky Way, and we did not find any serious tension with General Relativity. We used the Schwarzschild-like metric of Scalar-Tensor-Vector-Gravity to predict the orbital motion of S2-star, and to compare it with the publicly available astrometric data, which include 145 measurements of the positions, 44 measurements of the radial velocities of S2-star along its orbit, and the recent measurement of the orbital precession. We employed a Monte Carlo Markov Chain algorithm to explore the parameter space, and constrained the only one additional parameter of Scalar-Tensor-Vector-Gravity to 0.410 at 99,7% confidence level, where = 0 reduces this modified theory of gravity to General Relativity.
Journal of Cosmology and Astroparticle Physics, Volume 2022, Issue 03, id.007, 27 pp., 2022
Despite the huge improvements guaranteed by future GRAVITY observations of the S0-2 star, these w... more Despite the huge improvements guaranteed by future GRAVITY observations of the S0-2 star, these will not be able to unveil the fundamental nature, whether black hole or wormhole, of the central supermassive object. Nevertheless, observing stars orbiting closer to the central gravitational source could allow to distinguish between the black hole and wormhole nature of this object at more than 5σ. Firstly, we have used publicly available astrometric and spectroscopic measurements of the S0-2 star to constrain the metric around the supermassive object without finding any evidence either favouring or ruling out the wormhole nature. Secondly, we have designed a mock catalogue of future observations of the S0-2 star mirroring the accuracy and precision of GRAVITY. Afterwards, we firstly tested our methodology showing that our procedure recovers the input model, and subsequently we demonstrated that the constraining power of such a dataset is not enough to distinguish between black hole and wormhole. Finally, we built some toy models representing stars orbiting much closer the central object than S0-2. We used these toy models to investigate which are the ideal orbital features and observational strategies to achieve our aim of unveiling the fundamental nature of the central supermassive object, demonstrating that a star with a period of the order of ~ 5 years and a pericentre distance of ~ 5 AU could identify the nature of the central object at almost 5σ accuracy.
Physical Review D, Volume 105, Issue 4, article id.044014, 2022
In this paper, we introduce the post-Minkowskian approximation of energy-momentum-squared gravity... more In this paper, we introduce the post-Minkowskian approximation of energy-momentum-squared gravity (EMSG). This approximation is used to study the gravitational energy flux in the context of EMSG. As an application of our results, we investigate the EMSG effect on the first time derivative of the orbital period of the binary pulsars. Utilizing this post-Keplerian parameter, the free parameter of the EMSG theory, f 0 , is estimated for six known binary pulsars. Taking the binaries that have the most accurate observations, it turns out that −6 × 10 −37 m s 2 kg −1 < f 0 < +10 −36 m s 2 kg −1. This bound is in agreement with the precedent studies.
Physical Review D, Volume 104, Issue 10, article id.L101502, 2021
The GRAVITY Collaboration achieved the remarkable detection of the orbital precession of the S2 s... more The GRAVITY Collaboration achieved the remarkable detection of the orbital precession of the S2 star around the Galactic centre supermassive black hole, providing yet another proof of the validity of the General Relativity. The departure from the Schwarzschild precession is encoded in the parameter fSP which multiplies the predicted general relativistic precession. Such a parameter results to be fSP = 1.10 ± 0.19, which is consistent with General Relativity (fSP = 1) at 1σ level. Nevertheless, this parameter may also hide an effect of modified theories of gravity. Thus, we consider the orbital precession due to the Yukawa-like gravitational potential arising in the weak field limit of f (R)-gravity, and we use the current bound on the fSP to constrain the strength and the scale length of the Yukawa-like potential. No deviation from GR are revealed at scale of λ < 6300 AU with the strength of the Yukawa potential restricted to δ = −0.01 +0.61 −0.14 .
Monthly Notices of the Royal Astronomical Society, Volume 504, Issue 2, pp.2868-2876, 2021
Dark matter as a Bose-Einstein condensate, such as the axionic scalar field particles of String T... more Dark matter as a Bose-Einstein condensate, such as the axionic scalar field particles of String Theory, can explain the coldness of dark matter on large scales. Pioneering simulations in this context predict a rich wave-like structure, with a ground state soliton core in every galaxy surrounded by a halo of excited states that interfere on the de Broglie scale. This de Broglie scale is largest for low mass galaxies as momentum is lower, providing a simple explanation for the wide cores of dwarf spheroidal galaxies. Here we extend these "wave dark matter" (ψDM) predictions to the newly discovered class of "Ultra Diffuse Galaxies" (UDG) that resemble dwarf spheroidal galaxies but with more extended stellar profiles. Currently the best studied example, DF44, has a uniform velocity dispersion of 33km/s, extending to at least 3 kpc, that we show is reproduced by our ψDM simulations with a soliton radius of 0.5 kpc. In the ψDM context, we show the relatively flat dispersion profile of DF44 lies between massive galaxies with compact dense solitons, as may be present in the Milky Way on a scale of 100pc and lower mass galaxies where the velocity dispersion declines centrally within a wide, low density soliton, like Antlia II, of radius 3 kpc.
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Papers by Ivan de Martino