Prospects on searches for baryonic Dark Matter produced in $${\varvec{b}}$$-hadron decays at LHCb

A model that can simultaneously explain Dark Matter relic density and the apparent matter anti-matter imbalance of the universe has been recently proposed. The model requires b-hadron branching fractions to Dark Matter at the per mille level. The b-hadrons decay to a dark sector baryon, $$\psi _{\mathrm{DS}}$$ ψ DS , which has a mass in the region $$940 ~\mathrm{MeV}/c^2\le m_{\psi _{\mathrm{DS}}}\le 4430~\mathrm{MeV}/c^2$$ 940 MeV / c 2 ≤ m ψ DS ≤ 4430 MeV / c 2 . In this paper, we discuss the sensitivity of the LHCb experiment to search for this dark baryon, covering different types of topology and giving prospects for Runs 3 and 4 of the LHC, as well as for the proposed Upgrade II. We show that the LHCb experiment can cover the entire mass range of the hypothetical dark baryon.

SDSS-IV MaNGA: radial gradients in stellar population properties of early-type and late-type galaxies

ABSTRACT We derive ages, metallicities, and individual element abundances of early- and late-type galaxies (ETGs and LTGs) out to 1.5 Re. We study a large sample of 1900 galaxies spanning 8.6–11.3 log M/M⊙ in stellar mass, through key absorption features in stacked spectra from the SDSS-IV/MaNGA survey. We use mock galaxy spectra with extended star formation histories to validate our method for LTGs and use corrections to convert the derived ages into luminosity- and mass-weighted quantities. We find flat age and negative metallicity gradients for ETGs and negative age and negative metallicity gradients for LTGs. Age gradients in LTGs steepen with increasing galaxy mass, from −0.05 ± 0.11 log Gyr/Re for the lowest mass galaxies to −0.82 ± 0.08 log Gyr/Re for the highest mass ones. This strong gradient–mass relation has a slope of −0.70 ± 0.18. Comparing local age and metallicity gradients with the velocity dispersion σ within galaxies against the global relation with σ shows that internal processes regulate metallicity in ETGs but not age, and vice versa for LTGs. We further find that metallicity gradients with respect to local σ show a much stronger dependence on galaxy mass than radial metallicity gradients. Both galaxy types display flat [C/Fe] and [Mg/Fe], and negative [Na/Fe] gradients, whereas only LTGs display gradients in [Ca/Fe] and [Ti/Fe]. ETGs have increasingly steep [Na/Fe] gradients with local σ reaching 6.50 ± 0.78 dex/log km s−1 for the highest masses. [Na/Fe] ratios are correlated with metallicity for both galaxy types across the entire mass range in our sample, providing support for metallicity-dependent supernova yields.

Possible bilepton resonances in like-sign pairs

We consider pair production of bileptons Y[Formula: see text]Y[Formula: see text] at the LHC for the presently accumulated integrated luminosity of 150/fb. It is shown that the entire mass range 800 GeV [Formula: see text]M(Y) [Formula: see text] 2000 GeV can be successfully searched. A bilepton resonance will have an exceptionally large ratio of signal to background because the Standard Model prediction is so infinitesimal. A 5[Formula: see text] discovery is quite feasible.

How the first stars shaped the faintest gas-dominated dwarf galaxies

Cosmological simulations predict that dark matter halos with circular velocities lower than 30 km/s should have lost most of their neutral gas by heating of the ultra-violet background. This is in stark contrast with gas-rich galaxies such as e.g. Leo T, Leo P and Pisces A, which all have circular velocities of ~15 km/s (Ryan-Weber et al. 2008, Bernstein-Cooper et al. 2014, Tollerud et al. 2015). We show that when we include feedback from the first stars into our models, simulated dwarfs have very different properties at redshift 0 than when this form of feedback is not included. Including this Population-III feedback leads to galaxies that lie on the baryonic Tully-Fisher relation over the entire mass range of star forming dwarf galaxies, as well as reproducing a broad range of other observational properties.