arXiv subjects

Emmanuel Nezri

Publications and source records attributed to Emmanuel Nezri.

14 recordsLinked to original sources

arXiv2025

Constraining self-interacting scalar field dark matter with strong gravitational lensing in cluster scale?

We present a method to investigate the properties of solitonic cores in the Thomas-Fermi regime under the self-interacting scalar field dark matter framework. Using semi-analytical techniques, we characterize soliton signatures through their density profiles, gravitational lensing deflection angles, and surface mass density excess in the context of strong lensing by galaxy clusters. Focusing on halos spanning two mass scales -- $M_{200}= 2 \cdot 10^{15}\rm M_\odot$ and $2 \cdot 10^{14} \rm M_\odot$ -- we compute lensing observables to assess the viability of the SFDM model. Our analysis establishes constraints on the soliton core mass, directly probing the self-interaction parameter space of scalar field dark matter. This work bridges semi-analytical predictions with astrophysical observations, offering a lensing-based framework to test ultralight dark matter scenarios in galaxy cluster environments.

astro-ph.CO↗

arXiv2022

Cosmological simulations of the same spiral galaxy: the impact of baryonic physics

The interplay of star formation and supernova (SN) feedback in galaxy formation is a key element for understanding galaxy evolution. Since these processes occur at small scales, it is necessary to have sub-grid models that recover their evolution and environmental effects at the scales reached by cosmological simulations. We simulate the same spiral galaxy inhabiting a Milky Way (MW) size halo in a cosmological environment changing the sub-grid models for SN feedback and star formation. We test combinations of the Schmidt law and a multi-freefall based star formation with delayed cooling feedback or mechanical feedback. We reach a resolution of 35 pc in a zoom-in box of 36 Mpc. For this, we use the code RAMSES with the implementation of gas turbulence in time and trace the local hydrodynamical features of the star-forming gas. Finally, we compare the galaxies at redshift 0 with global and interstellar medium observations in the MW and local spiral galaxies. The simulations show successful comparisons with observations. Nevertheless, diverse galactic morphologies are obtained from different numerical implementations. We highlight the importance of detailed modelling of the star formation and feedback processes, especially when increasing the resolution of simulations. Future improvements could alleviate the degeneracies exhibited in our simulated galaxies under different sub-grid models.

astro-ph.GA↗

arXiv2022

Morphology of dark matter haloes beyond triaxiality

The morphology of haloes inform about both cosmological and galaxy formation models. We use the Minkowski Functionals (MFs) to characterize the actual morphology of haloes, only partially captured by smooth density profile, going beyond the spherical or ellipsoidal symmetry. We employ semi-analytical haloes with NFW and $αβγ$-profile and spherical or ellipsoidal shape to obtain a clear interpretation of MFs as function of inner and outer slope, concentration and sphericity parameters. We use the same models to mimic the density profile of $N$-body haloes, showing that their MFs clearly differ as sensitive to internal substructures. This highlights the benefit of MFs at the halo scales as promising statistics to improve the spatial modeling of dark matter, crucial for future lensing, Sunyaev-Zel'dovich, and X-ray mass maps as well as dark matter detection based on high-accuracy data.

astro-ph.CO↗

arXiv2021

Testing the predictions of axisymmetric distribution functions of galactic dark matter with hydrodynamical simulations

Signal predictions for galactic dark matter (DM) searches often rely on assumptions on the DM phase-space distribution function (DF) in halos. This applies to both particle (e.g. $p$-wave suppressed or Sommerfeld-enhanced annihilation, scattering off atoms, etc.) and macroscopic DM candidates (e.g. microlensing of primordial black holes). As experiments and observations improve in precision, better assessing theoretical uncertainties becomes pressing in the prospect of deriving reliable constraints on DM candidates or trustworthy hints for detection. Most reliable predictions of DFs in halos are based on solving the steady-state collisionless Boltzmann equation (e.g. Eddington-like inversions, action-angle methods, etc.) consistently with observational constraints. One can do so starting from maximal symmetries and a minimal set of degrees of freedom, and then increasing complexity. Key issues are then whether adding complexity, which is computationally costy, improves predictions, and if so where to stop. Clues can be obtained by making predictions for zoomed-in hydrodynamical cosmological simulations in which one can access the true (coarse-grained) phase-space information. Here, we test an axisymmetric extension of the Eddington inversion to predict the full DM DF from its density profile and the total gravitational potential of the system. This permits to go beyond spherical symmetry, and is a priori well suited for spiral galaxies. We show that axisymmetry does not necessarily improve over spherical symmetry because the (observationally unconstrained) angular momentum of the DM halo is not generically aligned with the baryonic one. Theoretical errors are similar to those of the Eddington inversion though, at the 10-20% level for velocity-dependent predictions related to particle DM searches in spiral galaxies. We extensively describe the approach and comment on the results.

astro-ph.CO↗

arXiv2020

Predicting the dark matter velocity distribution in galactic structures: tests against hydrodynamic cosmological simulations

Reducing theoretical uncertainties in Galactic dark matter (DM) searches is an important challenge as several experiments are now delving into the parameter space relevant to popular (particle or not) candidates. Since many DM signal predictions rely on the knowledge of the DM velocity distribution---direct searches, capture by stars, p-wave-suppressed or Sommerfeld-enhanced annihilation rate, microlensing of primordial black holes, etc.---it is necessary to assess the accuracy of our current theoretical handle. Beyond Maxwellian approximations or ad-hoc extrapolations of fits on cosmological simulations, approaches have been proposed to self-consistently derive the DM phase-space distribution only from the detailed mass content of the Galaxy and some symmetry assumptions (e.g. the Eddington inversion and its anisotropic extensions). Although theoretically sound, these methods are still based on simplifying assumptions and their relevance to real galaxies can be questioned. In this paper, we use zoomed-in cosmological simulations to quantify the associated uncertainties. Assuming isotropy, we predict the speed distribution and its moments from the DM and baryonic content measured in simulations, and compare them with the true ones. Taking as input galactic mass models fitted on full simulation data, we reach a predictivity down to ~ 10% for some velocity-related observables, significantly better than some Maxwellian models. This moderate theoretical error is particularly encouraging at a time when stellar surveys like the Gaia mission should allow us to improve constraints on Galactic mass models.

astro-ph.GA↗

arXiv2015

CLUMPY: Jeans analysis, $γ$-ray and neutrino fluxes from dark matter (sub-)structures

We present an update of the CLUMPY code for the calculation of the astrophysical J-factors (from dark matter annihilation/decay) for any Galactic or extragalactic dark matter halo including substructures: halo-to-halo concentration scatter may now be enabled, boost factors can include several levels of substructures, and triaxiality is a new option for dark matter haloes. This new version takes advantage of the CFITSIO and HEALPix libraries to propose FITS output maps using the HEALPix pixelisation scheme. Skymaps for $γ$-ray and $ν$ signals from generic annihilation/decay spectra are now direct outputs of CLUMPY. Making use of HEALPix routines, smoothing by a user-defined instrumental Gaussian beam and computing the angular power spectrum of the maps is now possible. In addition to these improvements, the main novelty is the implementation of a Jeans analysis module, to obtain dark matter density profiles from kinematic data in relaxed spherical systems (e.g., dwarf spheroidal galaxies). The code is also interfaced with the GreAT toolkit designed for Markov Chain Monte Carlo analyses, from which probability density functions and credible intervals can be obtained for velocity dispersions, dark matter profiles, and J-factors.

astro-ph.CO↗

arXiv2014

Baryonic and dark matter distribution in cosmological simulations of spiral galaxies

We study three cosmological hydrodynamical simulations of Milky Way(MW)-sized halos including a comparison with the dark matter(DM)-only counterparts. We find one of our simulated galaxies with interesting MW-like features. Thanks to a consistently tuned star formation rate and supernovae feedback we obtain an extended disk and a flat rotation curve with a satisfying circular velocity and a reasonable DM density in the solar neighbourhood. Mimicking observational methods, we re-derive the stellar mass and obtain stellar-to-halo mass ratios reduced by more than 50\%. We show the interaction between the baryons and the dark matter which is first contracted by star formation and then cored by feedback processes. Indeed, we report an unprecedentedly observed effect in the DM density profile consisting of a central core combined with an adiabatic contraction at larger galactic radii. The cores obtained are typically $\sim$ 5 kpc large. Moreover, this also impacts the DM density at the solar radius. In our simulation resembling most to the MW, the density is raised from 0.23 GeV/cm$^3$ in the dark matter only run to 0.36 GeV/cm$^3$ (spherical shell) or 0.54 GeV/cm$^3$ (circular ring) in the hydrodynamical run. Studying the subhalos, the dark matter within luminous satellites is also affected by baryonic processes and exihibits cored profiles whereas dark satellites are cuspy. We find a shift in mass compared to DM-only simulations and obtain, for halos in the lower MW mass range, a distribution of luminous satellites comparable to the MW spheroidal dwarf galaxies.

astro-ph.GA↗

arXiv2012

Indirect dark matter searches: towards a consistent top-bottom approach for studying the gamma-ray signals and associated backgrounds

While dark matter (DM) is the key ingredient for a successful theory of structure formation, its microscopic nature remains elusive. Indirect detection may provide a powerful test for some strongly motivated DM particle models. Nevertheless, astrophysical backgrounds are usually expected with amplitudes and spectral features similar to the chased signals. On galactic scales, these backgrounds arise from interactions of cosmic rays (CRs) with the interstellar gas, both being difficult to infer and model in detail from observations. Moreover, the associated predictions unavoidably come with theoretical errors, which are known to be significant. We show that a trustworthy guide for such challenging searches can be obtained by exploiting the full information contained in cosmological simulations of galaxies, which now include baryonic gas dynamics and star formation. We further insert CR production and transport from the identified supernova events and fully calculate the CR distribution in a simulated galaxy. We focus on diffuse gamma-rays, and self-consistently calculate both the astrophysical galactic emission and the dark matter signal. We notably show that adiabatic contraction does not necessarily induce large signal-to-noise ratios in galactic centers, and could anyway be traced from the astrophysical background itself. We finally discuss how all this may be used as a generic diagnostic tool for galaxy formation.

astro-ph.HE↗

arXiv2009

Positrons and antiprotons from inert doublet model dark matter

In the framework of the Inert Doublet Model, a very simple extension of the Standard Model, we study the production and propagation of antimatter in cosmic rays coming from annihilation of a scalar dark matter particle. We consider three benchmark candidates, all consistent with the WMAP cosmic abundance and existing direct detection experiments, and confront the predictions of the model with the recent PAMELA, ATIC and HESS data. For a light candidate, M_{DM} = 10 GeV, we argue that the positron and anti-proton fluxes may be large, but still consistent with expected backgrounds, unless there is an enhancement (boost factor) in the local density of dark matter. There is also a substantial anti-deuteron flux which might be observable by future experiments. For a candidate with M_{DM} = 70 GeV, the contribution to positron and anti-proton fluxes is much smaller than the expected backgrounds. Even if a boost factor is invoked to enhance the signals, the candidate is unable to explain the observed positron and anti-proton excesses. Finally, for a heavy candidate, M_{DM} = 10 TeV, it is possible to fit the PAMELA excess (but, unfortunately, not the ATIC one) provided there is a large enhancement, either in the local density of dark matter or through the Sommerfeld effect.

hep-ph↗

arXiv2007

The Inert Doublet Model: an Archetype for Dark Matter

The Inert Doublet Model (IDM), a two Higgs extension of the Standard Model with an unbroken $Z_2$ symmetry, is a simple and yet rich model of dark matter. We present a systematic analysis of the dark matter abundance and investigate the potentialities for direct and gamma indirect detection. We show that the model should be within the range of future experiments, like GLAST and ZEPLIN. The lightest stable scalar in the IDM is a perfect example, or archetype of a weakly interacting massive particle.

hep-ph↗

arXiv2006

The Suppression of Neutralino Annihilation into Zh

The Indirect Detection of neutralino Dark Matter is most promising through annihilation channels producing a hard energy spectrum for the detected particles, such as the neutralino annihilation into $Zh$. A cancellation however makes this particular annihilation channel generically subdominant in the huge parameter space of supersymmetric models. This cancellation requires non-trivial relations between neutralino mixings and masses, which we derive from gauge independence and unitarity of the MSSM. To show how the cancellation overshoots leaving only a subdominant result, we use a perturbative expansion in powers of the electroweak/supersymmetry breaking ratio $m_{Z}/m_χ$.

hep-ph↗

arXiv2004

Direct and Indirect Detection of Dark Matter in Heterotic Orbifold Models

We study the neutralino dark matter phenomenology in the context of effective field theories derived from the weakly--coupled heterotic string. We consider in particular direct detection and indirect detection with neutrino telescopes rates. The two cases of moduli dominated and dilaton dominated SUSY breaking lead to completely different phenomenologies. Even if in both cases relic density constraints can be fulfilled, moduli domination generically leads to detection rates which are much below the present and future experimental sensitivities, whereas dilaton domination gives high detection rates accessible to the next generation of experiments. This could make dark matter searches an alternative way to constrain high energy fundamental parameters.

hep-ph↗

arXiv2004

Neutrinos from Dark Matter annihilations at the Galactic Centre

We discuss the prospects for detection of high energy neutrinos from dark matter annihilation at the Galactic centre. Despite the large uncertainties associated with our poor knowledge of the distribution of dark matter in the innermost regions of the Galaxy, we determine an upper limit on the neutrino flux by requiring that the associated gamma-ray emission does not exceed the observed flux. We conclude that if dark matter is made of neutralinos, a neutrino flux from dark matter annihilations at the GC will not be observable by Antares. Conversely, the positive detection of such a flux would either require an alternative explanation, in terms of astrophysical processes, or the adoption of other \DM candidates, disfavouring the case for neutralinos.

astro-ph↗

arXiv2003

Neutrino Oscillations v.s. Leptogenesis in SO(10) Models

We study the link between neutrino oscillations and leptogenesis in the minimal framework assuming an SO(10) see-saw mechanism with 3 families. Dirac neutrino masses being fixed, the solar and atmospheric data then generically induce a large mass-hierarchy and a small mixing between the lightest right-handed neutrinos, which fails to produce sufficient lepton asymmetry by 5 orders of magnitudes at least. This failure can be attenuated for a very specific value of the mixing sin^2(2θ_{e3})=0.1, which interestingly lies at the boundary of the CHOOZ exclusion region, but will be accessible to future long baseline experiments.

hep-ph↗