arXiv subjects

Patrick Valageas

Publications and source records attributed to Patrick Valageas.

At least 19 recordsLinked to original sources

arXiv2026

Repulsive dark matter from Hosotani mechanism

We build an ultralight dark matter model with repulsive self-interactions, starting from a 5D action that only includes a $U(1)$ gauge field and several massive and charged free fermions. The dark matter scalar field corresponds to the fifth component of the gauge field, after compactification to 4D. Although the single-fermion case only leads to attractive self-interactions, two fermions can already give rise to repulsive self-interactions, thanks to a Scherk-Schwarz twist around the fifth dimension. We check the observational and theoretical self-consistency of this scenario, from the inflation stage to the current time. We find that large ranges of model parameters are allowed. For scalar masses below $10^{-12}$ eV the self-interactions are negligible and the model behaves as fuzzy dark matter. For higher masses the repulsive self-interactions govern the formation of solitons of astrophysical size. Larger sizes require a large initial misalignment or small masses in the fuzzy dark matter regime.

astro-ph.CO↗

arXiv2025

Burgers dynamics for Poisson point process initial conditions of the Weibull class

We derive the statistical properties of one-dimensional Burgers dynamics with stochastic initial conditions for the velocity potential defined by a Poisson point process whose intensity follows a power law with exponent $\alpha > -1$. Working in the inviscid limit and exploiting the geometrical construction of solutions in terms of first-contact parabolas, we derive explicit analytical expressions for a broad set of statistical quantities. These include the one- and two-point probability distributions of the velocity, the multiplicity functions of voids and shocks, and the velocity and density correlation functions together with their associated power spectra. We also show that the full hierarchy of $n$-point distributions factorizes into a sequence of two-point conditional probabilities. This class of initial conditions leads to self-similar evolution and produces probability distributions characterized by stretched-exponential tails, with tail exponents spanning the full range from unity to infinity. The associated characteristic length scale grows as a power law of time, with an exponent lying between zero and one half.

cond-mat.stat-mech↗

arXiv2025

Burgers dynamics for Poisson point process initial conditions

We investigate the statistical properties of one-dimensional Burgers dynamics evolving from stochastic initial conditions defined by a Poisson point process for the velocity potential, with a power-law intensity. Thanks to the geometrical interpretation of the solution in the inviscid limit, in terms of first-contact parabolas, we obtain explicit results for the multiplicity functions of shocks and voids, and for velocity and density one- and two-point correlation functions and power spectra. These initial conditions gives rise to self-similar dynamics with probability distributions that display power-law tails. In the limit where the exponent $\alpha$ of the Poisson process that defines the initial conditions goes to infinity, the power-law tails steepen to Gaussian falloffs and we recover the spatial distributions obtained in the classical study by Kida (1979) of Gaussian initial conditions with vanishing large-scale power.

cond-mat.stat-mech↗

arXiv2025

Testing scalar dark matter clumps with Pulsar Timing Arrays

Scalar dark matter is a viable alternative to particle dark matter models such as Weakly Interacting Massive Particles (WIMPS). This is particularly the case for scalars with a low mass $m \gtrsim 10^{-21} {\rm eV}$ as required to make quantum effects macroscopic on galactic scales. We point out that by synchronising the measurements of arrival times of pairs of pulsars, Pulsar Timing Arrays (PTA) could probe ultralight dark matter (ULDM) scenarios with a mass $10^{-23} {\rm eV}\lesssim m \lesssim 10^{-19} {\rm eV}$ that is greater than the one reached in standard analysis. The upper limit on the mass $m$ is set by the time lag $\Delta t$ between the observations of the two pulsars and could be pushed above $10^{-19} {\rm eV}$ for $\Delta t$ smaller than one hour. However, for these high scalar masses only very high density dark matter clouds could be detected and the capture rate of neutron stars is too low to provide sufficient statistics. Significant detection probabilities would thus require direct dark-matter-baryon interactions that favor the formation of neutron stars within such dark matter clouds, or the discovery of black hole/pulsar binary systems, taking advantage of the dark matter spike generated by the black hole.

astro-ph.CO↗

arXiv2025

Vortices and rotating solitons in ultralight dark matter

The dynamics of ultralight dark matter with non-negligible self-interactions are determined by a nonlinear Schr\"odinger equation rather than by the Vlasov equation of collisionless particles. This leads to wave-like effects, such as interferences, the formation of solitons, and a velocity field that is locally curl-free, implying that vorticity is carried by singularities associated with vortices. Using analytical derivations and numerical simulations in 2D, we study the evolution of such a system from stochastic initial conditions with nonzero angular momentum. Focusing on the Thomas-Fermi regime, where the de Broglie wavelength of the system is smaller than its size, we show that a rotating soliton forms in a few dynamical times. The rotation is not associated with a large orbital quantum number of the wave function. Instead, it is generated by a regular lattice of vortices that gives rise to a solid-body rotation in the continuum limit. Such rotating solitons have a maximal radius and rotation rate for a given central density, while the vortices follow the matter flow on circular orbits. We show that this configuration is a stable minimum of the energy at fixed angular momentum and we check that the numerical results agree with the analytical derivations. We expect most of these properties to extend to the 3D case where point vortices would be replaced by vortex rings.

astro-ph.CO↗

arXiv2024

Formation of solitons and their transitions in scalar-field dark matter models with a non-polynomial self-interaction potential

We study the formation of solitons inside scalar-field dark matter halos with a non-polynomial self-interaction potential. We consider a self-interaction potential that is quartic in the scalar field in the low-density regime but saturates at large densities. This mimics the behaviour of axion monodromy potentials. We concentrate on the semi-classical regime, where the de Broglie wavelength is much smaller than the size of the system. We find that depending on the strength and scale of the self-interactions, the system can form solitons of the Thomas-Fermi type (dominated by self-interactions) or of the Fuzzy Dark Matter type (dominated by the quantum pressure). The system can also display transitions from a Thomas-Fermi soliton to a Fuzzy Dark Matter soliton as the former becomes unstable. We show that these behaviours can be understood from a simple Gaussian ansatz. We find that even in cases where the self-interactions are always subdominant they can play a critical role, by providing a small density boost that is enough to generate the seed for the formation of a Fuzzy Dark Matter soliton at much later times. We also point out that the intuition derived from a hydrodynamical picture can be misleading in regimes where wave effects are important.

astro-ph.CO↗

arXiv2024

Constraining Self-interacting Scalar Field Dark Matter From the Black Hole Shadow of the Event Horizon Telescope

An exciting possibility to constrain dark matter (DM) scenarios is to search for their gravitational imprints on Black Hole (BH) observations. In this paper, we investigate the impact of self-interacting scalar field DM on the shadow radius of a Schwarzschild BH. We implement a self-consistent formulation, paying attention to the enhancement of the DM density due to the BH gravitational influence and the accretion flow onto the BH. First, we calculate the first-order correction to the shadow radius caused by a general DM environment. Then, we apply this perturbative method to the case of self-interacting scalar field DM and derive analytical expressions for the critical impact parameter. We find that self-consistency requirements, involving the lifetime and the mass of the central DM soliton, or the mass and the size of the extended virialized DM halo, ensure that the impact of the DM environment on the shadow radius is below the observational upper bound. This emphasizes the importance of taking into account the self-consistency constraints of the underlying DM scenario, which can strongly limit the range of possible DM density profiles and their impact on the shadow radius.

astro-ph.CO↗

arXiv2024

Detecting dark matter oscillations with gravitational waveforms

We consider the phase shift in the gravitational wave signal induced by fast oscillations of scalar dark matter surrounding binary systems, which could be probed by the future experiments LISA and DECIGO. This effect depends on the local matter density and the mass of the dark matter particle. We compare it to the phase shift due to a standard dynamical friction term, which should generically be present. We find that the effect associated with the oscillations only dominates over the dynamical friction for dark matter masses below $10^{-21}$ eV, with masses below $10^{-23}$ eV implying cloud sizes that are too large to be realistic. Moreover, for masses of the order of $10^{-21}$ eV, LISA and DECIGO would only detect this effect for dark matter densities greater than that in the solar system by a factor $10^5$ or $10^4$ respectively. We conclude that this signal can be ignored for most dark matter scenarios unless very dense clouds of very light dark matter are created early in the Universe at a redshift $z\sim 10^4$.

astro-ph.CO↗

arXiv2023

The cosmological analysis of X-ray cluster surveys V. The potential of cluster counts in the $1<z<2$ range

Cosmological studies have now entered Stage IV according to the Dark Energy Task Force prescription, thanks to new missions (Euclid, Rubin Observatory, SRG/eROSITA) that are expected to provide the required ultimate accuracy in the dark energy (DE) equation of state (EoS). However, none of these projects have the power to systematically unveil the galaxy cluster population at $z>1$. There therefore remains the need for an ATHENA-like mission to run independent cosmological investigations and scrutinise the consistency between the results from the $0 1$. Such samples will allow a detailed modelling of the evolution of cluster physics along with a standalone cosmological analysis. Our results suggest that survey B has the optimal design as it provides greater statistics. Remarkably, high-$z$ clusters, despite representing 15% or less of the full samples, allow a significant reduction of the uncertainty on the cosmological parameters: $\Delta w_a$ is reduced by a factor of 2.3 and $\Delta f_{NL}^{loc}$ by a factor of 3. Inventorying the high-$z$ X-ray cluster population can play a crucial role in ensuring overall cosmological consistency. This will be the major aim of future new-generation ATHENA-like missions.

astro-ph.CO↗

arXiv2023

Supersonic friction of a black hole traversing a self-interacting scalar dark matter cloud

Black Holes (BH) traversing a dark matter cloud made out of a self-interacting scalar soliton are slowed down by two complementary effects. At low subsonic speeds, the BH accretes dark matter and this is the only source of dragging along its motion, if we neglect the backreaction of the cloud self-gravity. The situation changes at larger supersonic speeds where a shock appears. This leads to the emergence of an additional friction term, associated with the gravitational and scalar pressure interactions and with the wake behind the moving BH. This is a long distance effect that can be captured by the hydrodynamical regime of the scalar flow far away from the BH. This dynamical friction term has the same form as the celebrated Chandrasekhar collisionless result, albeit with a well-defined Coulomb logarithm and a prefactor that is smaller by a factor 2/3. The infra-red cut-off is naturally provided by the size of the scalar cloud, which is set by the scalar mass and coupling, whilst the ultra-violet behaviour corresponds to the distance from the BH where the velocity field is significantly perturbed by the BH, which is determined by pressure effects. As a result, supersonic BH are slowed down by both the accretion drag and the dynamical friction. This effect will be potentially detectable by future gravitational wave experiments as it influences the phase of the gravitational wave signal from inspiralling binaries.

astro-ph.CO↗

arXiv2023

Gravitational waves from binary black holes in a self-interacting scalar dark matter cloud

We investigate the imprints of accretion and dynamical friction on the gravitational-wave signals emitted by binary black holes embedded in a scalar dark matter cloud. As a key feature in this work, we focus on scalar fields with a repulsive self-interaction that balances against the self-gravity of the cloud. To a first approximation, the phase of the gravitational-wave signal receives extra correction terms at $-3$PN, $-4$PN and $-5.5$PN orders, relative to the prediction of vacuum general relativity, due to cloud gravity, accretion and dynamical friction. Future observations by LISA and B-DECIGO have the potential to detect these effects for a large range of scalar masses~$m_\mathrm{DM}$ and self-interaction couplings~$\lambda_4$. This would correspond to scenarios with dark matter clouds smaller than $0.1$ pc, which would be difficult to detect by other probes.

astro-ph.CO↗

arXiv2023

Solitons and halos for self-interacting scalar dark matter

We study the formation and evolution of solitons supported by repulsive self-interactions inside extended halos, for scalar-field dark matter scenarios. We focus on the semiclassical regime where the quantum pressure is typically much smaller than the self-interactions. We present numerical simulations, with initial conditions where the halo is described by the WKB approximation for its eigenfunction coefficients. We find that when the size of the system is of the order of the Jeans length associated with the self-interactions, a central soliton quickly forms and makes about 50% of the total mass. However, if the halo is ten times greater than this self-interaction scale, a soliton only quickly forms in cuspy halos where the central density is large enough to trigger the self-interactions. If the halo has a flat core, it takes a longer time for a soliton to appear, after small random fluctuations on the de Broglie wavelength size build up to reach a large enough density. In some cases, we observe the co-existence of several narrow density spikes inside the larger self-interaction-supported soliton. All solitons appear robust and slowly grow, unless they already make up 40% of the total mass. We develop a kinetic theory, valid for an inhomogeneous background, to estimate the soliton growth rate for low masses. It explains the fast falloff of the growth rate as resonances between the ground state and halo excited states disappear. Our results suggest that cosmological halos would show a large scatter for their soliton mass, depending on their assembly history.

astro-ph.CO↗

arXiv2023

The Invisible Dilaton

We analyse the dynamics of a light scalar field responsible for the $\mu$ term of the Higgs potential and coupled to matter via the Higgs-portal mechanism. We find that this dilaton model is stable under radiative corrections induced by the standard model particle masses. When the background value of the scalar field is stabilised at the minimum of the scalar potential, the scalar field fluctuations only couple quadratically to the massive fields of the standard model preventing the scalar direct decay into standard model particles. Cosmologically and prior to the electroweak symmetry breaking, the scalar field rolls down along its effective potential before eventually oscillating and settling down at the electroweak minimum. These oscillations can be at the origin of dark matter due to the initial misalignment of the scalar field compared to the electroweak minimum, and we find that, when the mass of the scalar field is less than the eV scale and acts as a condensate behaving like dark matter on large scales, the scalar particles cannot thermalise with the standard model thermal bath. As matter couples in a composition-dependent manner to the oscillating scalar, this could lead to a violation of the equivalence principle aboard satellites such as the MICROSCOPE experiment and the next generation of tests of the equivalence principle. Local gravitational tests are evaded thanks to the weakness of the quadratic coupling in the dark matter halo, and we find that, around other sources, these dilaton models could be subject to a screening akin to the symmetron mechanism.

hep-ph↗

arXiv2022

Subsonic accretion and dynamical friction for a black hole moving through a self-interacting scalar dark matter cloud

We investigate the flow around a black hole moving through a cloud of self-interacting scalar dark matter. We focus on the large scalar mass limit, with quartic self-interactions, and on the subsonic regime. We show how the scalar field behaves as a perfect gas of adiabatic index $\gamma_{\rm ad}=2$ at large radii while the accretion rate is governed by the relativistic regime close to the Schwarzschild radius. We obtain analytical results thanks to large-radius expansions, which are also related to the small-scale relativistic accretion rate. We find that the accretion rate is greater than for collisionless particles, by a factor $c/c_s \gg 1$, but smaller than for a perfect gas, by a factor $c_s/c \ll 1$, where $c_s$ is the speed of sound. The dynamical friction is smaller than for a perfect gas, by the same factor $c_s/c \ll 1$, and also smaller than Chandrasekhar's result for collisionless particles, by a factor $c_s/(cC)$, where $C$ is the Coulomb logarithm. It is also smaller than for fuzzy dark matter, by a factor $v_0/c \ll 1$.

astro-ph.CO↗

arXiv2022

Self-similar solutions for Fuzzy Dark Matter

Fuzzy Dark Matter (FDM) models admit self-similar solutions which are very different from their Cold Dark Matter (CDM) counterparts and do not converge to the latter in the semiclassical limit. In contrast with the familiar CDM hierarchical collapse, they correspond to an inverse-hierarchy blow-up. Constant-mass shells start in the nonlinear regime, at early times, with small radii and high densities, and expand to reach at late times the Hubble flow, up to small linear perturbations. Thus, larger masses become linear first. This blow-up approximately follows the Hubble expansion, so that the central density contrast remains constant with time, although the width of the self-similar profile shrinks in comoving coordinates. As in a gravitational cooling process, matter is ejected from the central peaks through successive clumps. As in wave systems, the velocities of the geometrical structures and of the matter do not coincide, and matter slowly moves from one clump to the next, with intermittent velocity bursts at the transitions. These features are best observed using the density-velocity representation of the nonrelativistic scalar field, or the mass-shell trajectories, than with the Husimi phase-space distribution, where an analogue of the Heisenberg uncertainty principle blurs the resolution in the position or velocity direction. These behaviours are due to the quantum pressure and the wavelike properties of the Schr\"odinger equation. Although the latter has been used as an alternative to N-body simulations for CDM, these self-similar solutions show that the semiclassical limit needs to be handled with care.

astro-ph.CO↗

arXiv2021

The XXL survey: XLVI. Forward cosmological analysis of the C1 cluster sample

We present the forward cosmological analysis of an $XMM$ selected sample of galaxy clusters out to a redshift of unity. Following our previous 2018 study based on the dn/dz quantity alone, we perform an upgraded cosmological analysis of the same XXL C1 cluster catalogue (178 objects), with a detailed account of the systematic errors. We follow the ASpiX methodology: the distribution of the observed X-ray properties of the cluster population is analysed in a 3D observable space (count rate, hardness ratio, redshift) and modelled as a function of cosmology. Compared to more traditional methods, ASpiX allows the inclusion of clusters down to a few tens of photons. We obtain an improvement by a factor of 2 compared to the previous analysis by letting the normalisation of the M-T relation and the evolution of the L-T relation free. Adding constraints from the XXL cluster 2-point correlation function and the BAO from various surveys decreases the uncertainties by 23 and 53 % respectively, and 62% when adding both. Switching to the scaling relations from the Subaru analysis, and letting free more parameters, our final constraints are $\sigma_8$ = $0.99^{+0.14}_{-0.23}$, $\Omega_m$ = 0.296 $\pm$ 0.034 ($S_8 = 0.98^{+0.11}_{-0.21}$) for the XXL sample alone. Finally, we combine XXL ASpiX, the XXL cluster 2-point correlation function and the BAO, with 11 free parameters, allowing for the cosmological dependence of the scaling relations in the fit. We find $\sigma_8$ = $0.793^{+0.063}_{-0.12}$, $\Omega_m$ = 0.364 $\pm$ 0.015 ($S_8 = 0.872^{+0.068}_{-0.12}$), but still compatible with Planck CMB at 2.2$\sigma$. The results obtained by the ASpiX method are promising; further improvement is expected from the final XXL cosmological analysis involving a cluster sample twice as large. Such a study paves the way for the analysis of the eROSITA and future Athena surveys.

astro-ph.CO↗

arXiv2020

Non-Relativistic Formation of Scalar Clumps as a Candidate for Dark Matter

We propose a new mechanism for the formation of dark matter clumps in the radiation era. We assume that a light scalar field is decoupled from matter and oscillates harmonically around its vacuum expectation value. We include self-interactions and consider the nonrelativistic regime. The scalar dynamics are described by a fluid approach where the fluid pressure depends on both quantum and self-interaction effects. When the squared speed of sound of the scalar fluid becomes negative, an instability arises and the fluctuations of the scalar energy-density field start growing. They eventually become nonlinear and clumps form. Subsequently, the clumps aggregate and reach a universal regime. Afterwards, they play the role of cold dark matter. We apply this mechanism first to a model with a negative quartic term stabilised by a positive self-interaction of order six, and then to axion monodromy, where a subdominant cosine potential corrects a mass term. In the first case, the squared speed of sound becomes negative when the quartic term dominates, leading to a tachyonic instability. For axion monodromy, the instability starts very slowly after the squared speed of sound first becomes negative and then oscillates around zero. Initially the density perturbations perform acoustic oscillations due to the quantum pressure. Eventually, they start growing exponentially due to a parametric resonance. In both scenarios, the scalar-field clumps span a wide range of scales and masses, running from the size of atoms to that of galactic molecular clouds, and from $10^{-3} \, {\rm gram}$ to thousands of solar masses. Because of finite-size effects, both from the source and the lens, these dark matter clumps are far beyond the reach of microlensing observations.

astro-ph.CO↗

arXiv2020

Lagrangian-space Gaussian ansatz for the matter redshift-space power spectrum and correlation function

We study the predictions for the matter redshift-space power spectrum and correlation function of a Lagrangian-space Gaussian ansatz introduced in a previous work. This model is a natural extension of the Zeldovich approximation, where the displacement and velocity power spectra are determined by the equations of motion, instead of being set equal to the linear power spectrum. It does not contain any free parameter. As for the real-space statistics, we find that this Lagrangian-space approach is much more efficient for the correlation functions than for the power spectra. The damping of the BAO oscillations is well recovered but there is a large smooth drift from the simulations in the power spectra. The multipoles of the correlation functions are well recovered on BAO scales, with an accuracy of $2\%$ for $\xi^s_0$ down to $10 h^{-1}$ Mpc, and of $3\%$ for $\xi^s_2$ down to $26 h^{-1}$ Mpc, at $z \geq 0.35$.

astro-ph.CO↗