arXiv subjects

Muhsin Aljaf

Publications and source records attributed to Muhsin Aljaf.

10 recordsLinked to original sources

arXiv2026

On the orbital eccentricities of primordial black hole binaries inside and outside of dark matter halos

Primordial black hole (PBH) binaries in the stellar mass range may still contribute a fraction of the detectable compact object binaries by LIGO and future GW observatories. PBH binaries at formation typically have very high eccentricities. In this paper, we study the eccentricity of stellar mass range PBH binaries from all formation channels and account for all evolutionary pathways. We simulate large samples of PBH binaries, tracking their full orbital evolution up to their merger or to the present day. For those that merge, we compute their GW strain, detectability, and eccentricity distributions for LISA, DECIGO, ET, CE, and aLIGO. We find that PBH binaries that evolve in isolation completely circularize by the time their GWs enter any GW band except for LISA's, where residual eccentricities of order $O(10^{-2})$ can exist. Binaries that become part of dark matter halos can have multiple binary-single interactions with other PBHs, especially if they reside in the more dense environments among them and can have higher eccentricities even at their late inspiral phase, probed by the GW observatories. Considering the current limits on the abundance of stellar mass range PBHs, we predict that LISA and DECIGO together would be able to probe $O(10^2)$ such binaries with $e>0.01$. If these future GW observatories in space can exclude such eccentric binaries, then limits on the PBH abundance can be improved by an order of magnitude.

astro-ph.CO↗

arXiv2026

Binary Black Holes population synthesis based on the current LVK observations

The ongoing observations from ground based gravitational-wave observatories have led to the detection of more than a hundred merger events between black holes. We use the LIGO-Virgo-KAGRA (LVK) observations from 2015 to early 2024, to test the population synthesis of these merging binaries; which will allow us to probe the formation mechanisms and environments of these black holes. We test if the current sample of binary black holes can be explained only by the merger of black holes coming from the collapse of the cores of massive stars, i.e. as just first generation black holes merging with each other. Those black holes' masses will roughly follow a power-law distribution. We also test if in addition to the merger between first generation black holes, there is evidence for a second population of black hole binaries in which at least one the binaries' members is the product of an earlier merger between black holes. These binaries are typically referred to as signals of hierarchical mergers. Such a population can possibly explain the observation of very massive black hole binaries by the LVK collaboration. We find that the LVK observations give a statistical preference in log-likelihood of up to $- 2 \Delta ln\mathcal{L} = -150$ or in log-Bayes factor of up to $ln\textrm{BF} = 71$, for the full sample of black hole binaries originating from a combination of black holes following a power-law distribution and black holes from hierarchical mergers. The ratio of black holes following a power-law mass-distribution to a mass-distribution expected from hierarchical mergers is found to be as high as one-to-one. We also consider that some of the LVK black hole merging binaries are the result of primordial black holes (PBHs), merging inside dark matter halos and in the intergalactic medium. Adding a third population is preferred. [abridged]

astro-ph.CO↗

arXiv2025

The Merger Rate of Primordial Black Holes

The merger rate of primordial black hole (PBH) binaries can be used to understand the source population of the merging black hole binaries observable through gravitational-waves (GWs) and also to constrain the possible contribution of PBHs to dark matter. In the literature, the PBH merger rate is calculated analytically, assuming that PBH binaries stay in isolation (i.e. are unperturbed) and evolve solely via GW emission during their entire lifetime. However, if some or all of dark matter consists of PBHs, then as cosmic structures grow, PBH binaries and single PBHs fall inside dark matter halos. In those halos, the PBH binaries' interactions with their environment significantly affect the subsequent evolution of their orbital properties. In this paper, we present a numerical framework that accurately calculates the total PBH merger rate by combining the evolution of isolated binaries outside halos with the dynamics of binaries inside halos. In our work we have found that the isolated binary channel is suppressed at low redshifts and dynamical interactions in halos reshape the merger rate evolution with time, accelerating some mergers. At redshifts of $\lesssim 2$ the total merger rate is a factor of $\simeq 50 \%$ higher than the results assuming that all PBH binaries effectively stay unperturbed until their merger. Our simulations provide a definitive calculation on the total PBH merger rates, that are currently being probed and constrained from gravitational-wave observations. We make our merger rates publicly available at Zenodo

astro-ph.HE↗

arXiv2025

Conservative limits on primordial black holes from the LIGO-Virgo-KAGRA observations

Primordial black holes (PBH) may constitute a considerable fraction of dark matter. In this work we use the recent observations by the LIGO-Virgo-KAGRA (LVK) collaborations to set direct limits on stellar-mass range PBHs. We evaluate the merger rates of PBH binaries by accounting for the binaries formed by two-body captures inside dark matter halos and by studying the evolution of PBH binaries inside such halos through binary-single interactions. Those type of interactions contribute to what is a minimum of PBH merger rates at low redshifts detectable by LVK. Thus, they allow us to derive what is the most conservative upper limits on the presence of merging PBH binaries in the gravitational-wave observations. We study both the case where PBHs have a monochromatic mass-distribution and the case where that distribution is described by a log-normal function. Our derived limits on the mass fraction of dark matter composed of PBHs is in the range of $10^{-4}$ to $2\times 10^{-2}$, depending on the exact assumptions relating to the PBH binaries properties. For reasonable assumptions on those PBH binaries' properties before their evolution inside dark matter halos, we get that fraction to be in the range of $10^{-3} - 10^{-2}$, for PBH masses of 5-80 $M_{\odot}$. Our work provide some of the most competitive limits in the mass range of 5-50 $M_{\odot}$. [abridged]

astro-ph.CO↗

arXiv2024

Simulating Binary Primordial Black Hole Mergers in Dark Matter Halos

Primordial black holes (PBHs), possibly constituting a non-negligible fraction of dark matter (DM), might be responsible for a number of gravitational wave events detected by LIGO/Virgo/KAGRA. In this paper, we simulate the evolution of PBH binaries in DM halos and calculate their merger rate up to redshift of 10. We assume that DM halos are made entirely by a combination of single PBHs and PBH binaries. We present the resulting merger rates from the two main channels that lead to merging PBH binaries: two-body captures and binary-single interactions. We account for alternative assumptions on the dark matter halo mass-concentration relationship versus redshift. We also study what impact the PBH mass distribution, centered in the stellar-mass range, has on the PBH merger rate that the ground-based gravitational-wave observatories can probe. We find that under reasonable assumptions on the abundance of PBH binaries relative to single PBHs, the binary-single interaction rates can be dominant over the two-body capture channel. Our work studies in detail the dynamics of PBHs inside DM halos, advancing our understanding on how the current gravitational-wave events constrain the properties of PBHs. Moreover, we make predictions in a redshift range to be probed by future observatories.

astro-ph.GA↗

arXiv2023

Solving the $H_{0}$ tension in $f(T)$ Gravity through Bayesian Machine Learning

Bayesian Machine Learning~(BML) and strong lensing time delay~(SLTD) techniques are used in order to tackle the $H_{0}$ tension in $f(T)$ gravity. The power of BML relies on employing a model-based generative process which already plays an important role in different domains of cosmology and astrophysics, being the present work a further proof of this. Three viable $f(T)$ models are considered: a power law, an exponential, and a squared exponential model. The learned constraints and respective results indicate that the exponential model, $f(T)=αT_{0}\left(1-e^{-p T / T_{0}}\right)$, has the capability to solve the $H_{0}$ tension quite efficiently. The forecasting power and robustness of the method are shown by considering different redshift ranges and parameters for the lenses and sources involved. The lesson learned is that these values can strongly affect our understanding of the $H_{0}$ tension, as it does happen in the case of the model considered. The resulting constraints of the learning method are eventually validated by using the observational Hubble data(OHD).

astro-ph.CO↗

arXiv2023

Assessing the foundation and applicability of some dark energy fluid models in the Dirac-Born-Infeld framework

In this paper, we will deepen the understanding of some fluid models proposed by other authors for the description of dark energy. Specifically, we will show that the so-called (Modified) Berthelot fluid is the hydrodynamic realization of the free Dirac-Born-Infeld theory and that the Dieterici fluid admits a non-relativistic $k$-essence formulation; for the former model the evolution of the scalar field will be written in terms of some cosmographic parameters. The latter model will also be tested using Machine Learning algorithms with respect to cosmic chronometers data, and results about the dynamics at a background level will be compared with those arising when other fluids (Generalized Chaplygin Gas and Anton-Schmidt) are considered. Due to some cosmic opacity effects, the background cosmology of universes filled by these inequivalent fluids, as they arise in physically different theories, may not be enough for discriminating among them. Thus, a perturbation analysis in the long-wavelength limit is carried out revealing a rich variety of possible behaviors. It will also be shown that the free Dirac-Born-Infeld theory cannot account for flat galactic rotation curves, and therefore we derive an appropriate relationship between the scalar field potential and the brane tension for achieving this goal; this provides an estimate for the dark matter adiabatic speed of sound inside the halo consistent with other literature. A certain relationship between the Newtonian gravitational potential within the galaxy and the Lagrangian potential in the non-relativistic regime for the (Modified) Berthelot fluid will also be enlightened.

gr-qc↗

arXiv2021

Constraints on interacting dark energy models through cosmic chronometers and Gaussian process

In this paper, after reconstructing the redshift evolution of the Hubble function by adopting Gaussian process techniques, we estimate the best-fit parameters for some flat Friedmann cosmological models based on a Modified Chaplygin Gas interacting with dark matter. In fact, the expansion history of the Universe will be investigated because passively evolving galaxies constitute cosmic chronometers. An estimate for the present-day values of the deceleration parameter, adiabatic speed of sound within the dark energy fluid, effective dark energy, and dark matter equation of state parameters is provided. By this, we mean that the interaction term between the two dark fluids, which breaks the Bianchi symmetries, will be interpreted as an effective contribution to the dark matter pressure similarly to the framework of the "Generalized Dark Matter". We investigate whether the estimates of the Hubble constant and of the present-day abundance of dark matter are sensitive to the dark matter - dark energy coupling. We will also show that the cosmic chronometers data favor a cold dark matter and that our findings are in agreement with the Le Châtelier-Braun principle according to which dark energy should decay into dark matter.

astro-ph.CO↗

arXiv2020

Potential-driven Inflation with Disformal Coupling to Gravity

In this paper, we investigate the potential-driven inflation models with a disformal coupling to Einstein Gravity, to find out the effects of such a coupling on these models. We consider a simple coupling form which introduces only one parameter, and three inflation models, namely the chaotic inflation, the Higgs inflation, and the monodromy inflation. We find that the disformal coupling can have some modifications to the observational variables of these models such as the power spectrum, the spectral index as well as the tensor/scalar ratio, although not too large due to the constraints on the disformal coupling parameter. With these modifications, one has the opportunity of improving models that lie on the edge of the favorable regions of Planck observational data, such as monodromy inflation. Moreover, the non-trivial sound speed of tensor perturbations (gravitational waves) may come out, due to the coupling of gravity and kinetic terms of the field.

hep-ph↗

arXiv2020

Phase space analysis and singularity classification for linearly interacting dark energy models

In this paper, applying the Hartman-Grobman theorem we carry out a qualitative late-time analysis of some unified dark energy-matter Friedmann cosmological models, where the two interact through linear energy exchanges, and the dark energy fluid obeys to the dynamical equation of state of Redlich-Kwong, Modified Berthelot, and Dieterici respectively. The identification of appropriate late-time attractors allows to restrict the range of validity of the free parameters of the models under investigation. In particular, we prove that the late-time attractors which support a negative deceleration parameter correspond to a de Sitter universe. We show that the strength of deviation from an ideal fluid for the dark energy does not influence the stability of the late-time attractors, as well as the values of all the cosmological parameters at equilibrium, but for the Hubble function (which represents the age of the universe). Our analysis also shows that a singularity in the effective equation of state parameter for the dark energy fluid is not possible within this class of models.

gr-qc↗