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تسجيل مستخدم جديدCosmological structure formation in scalar field dark matter with repulsive self-interaction: The Incredible Shrinking Jeans Mass
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Scalar Field Dark Matter (SFDM) comprised of ultralight ($gtrsim 10^{-22}$ eV) bosons is an alternative to standard, collisionless Cold Dark Matter (CDM) that is CDM-like on large scales but inhibits small-scale structure formation. As a Bose-Einstein condensate, its free-field (fuzzy) limit (FDM) suppresses structure below the de Broglie wavelength, $lambda_text{deB}$, creating virialized haloes with central cores of radius $simlambda_text{deB}$, surrounded by CDM-like envelopes, and a halo mass function (HMF) with a sharp cut-off on small scales. With a strong enough repulsive self-interaction (SI), structure is inhibited, instead, below the Thomas-Fermi (TF) radius, $R_text{TF}$ (the size of an SI-pressure-supported ($n=1$)-polytrope), when $R_text{TF} > lambda_text{deB}$. Previously, we developed tools to describe SFDM dynamics on scales above $lambda_text{deB}$ and showed that SFDM-TF haloes formed by Jeans-unstable collapse from non-cosmological initial conditions have $R_text{TF}$-sized cores, surrounded by CDM-like envelopes. Revisiting SFDM-TF in the cosmological context, we simulate halo formation by cosmological infall and collapse, and derive its transfer function from linear perturbation theory to produce cosmological initial conditions and predict statistical measures of structure formation, such as the HMF. Since FDM and SFDM-TF transfer functions both have small-scale cut-offs, we can align them to let observational constraints on FDM proxy for SFDM-TF, finding FDM with particle masses $1 lesssim m/(10^{-22} text{ eV}/c^2) lesssim 30$ corresponds to SFDM-TF with $10 gtrsim R_text{TF}/(1 text{ pc}) gtrsim 1$, favoring sub-galactic (sub-kpc) core-size. The SFDM-TF HMF cuts off gradually, however, leaving more small-mass haloes: its Jeans mass shrinks so fast, scales filtered early can still recover and grow!
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Scalar Field Dark Matter (SFDM) comprised of ultralight bosons has attracted great interest as an alternative to standard, collisionless Cold Dark Matter (CDM) because of its novel structure-formation dynamics, described by the coupled Schrodinger-Po
isson equations. In the free-field (fuzzy) limit of SFDM (FDM), structure is inhibited below the de Broglie wavelength, but resembles CDM on larger scales. Virialized haloes have solitonic cores of radius $simlambda_text{deB}$, surrounded by CDM-like envelopes. When a strong enough repulsive self-interaction (SI) is also present, structure can be inhibited below a second length scale, $lambda_text{SI}$, with $lambda_text{SI}> lambda_text{deB}$ -- called the Thomas-Fermi (TF) regime. FDM dynamics differs from CDM because of quantum pressure, and SFDM-TF differs further by adding SI pressure. In the small-$lambda_text{deB}$ limit, however, we can model all three by fluid conservation equations for a compressible, $gamma=5/3$ ideal gas, with ideal gas pressure sourced by internal velocity dispersion and, for the TF regime, an added SI pressure, $P_text{SI}propto rho^2$. We use these fluid equations to simulate halo formation from gravitational collapse in 1D, spherical symmetry, demonstrating for the first time that SFDM-TF haloes form with cores the size of $R_text{TF}$, the radius of an SI-pressure-supported $(n=1)$-polytrope, surrounded by CDM-like envelopes. In comparison with rotation curves of dwarf galaxies in the local Universe, SFDM-TF haloes pass the [too-big-to-fail + cusp-core]-test if $R_text{TF}gtrsim 1$ kpc.
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