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We propose a general model where quintessence couples to electromagnetism via its kinetic term. This novelty generalizes the linear dependence of the gauge kinetic function on $\phi$, commonly adopted in the literature. The interaction naturally induces a time variation of the fine-structure constant that can be formulated within a disformally coupled framework, akin to a Gordon metric. Through a suitable parametrization of the scalar field and the coupling function, we test the model against observations sensitive to the variation of $\alpha$. We undertake a Bayesian analysis to infer the free parameters with data from Earth based, astrophysical and early Universe experiments. We find that the evolution of $\alpha$ is specific to each cosmological era and slows down at late times when dark energy accelerates the Universe. While the most stringent bound on the interaction is obtained from atomic clocks measurements, the quasars provide a constraint consistent with weak equivalence principle tests. This promising model is to be further tested with upcoming and more precise astrophysical measurements, such as those of the ESPRESSO spectrograph., Comment: 15 pages, 9 figures, 2 tables. V2: matches published version

In this work we study the growth of cold dark matter density perturbations in the nonlinear regime on a conformally coupled quintessence model in which the background is designed to mimic a $��$CDM cosmology. The spherical collapse of overdense regions is analyzed. We highlight the role of the coupling on the overall dynamics, trace the evolution of the density contrast throughout the cosmic history and compute perturbative parameters such as the critical density contrast. We find that the coupling has the influence of delaying the collapse due to the slower growth of matter perturbations. We follow to compute the cluster number counts using the Press-Schechter and Sheth-Tormen mass functions. In both cases, the transfer of energy between the dark energy field and dark matter suppresses the number of objects at low redshifts and enhances the number at high redshifts. Finally, we compute the expected cluster number counts for the future eROSITA mission and the current South Pole Telescope survey., 11 pages, 9 figures. V2: Matches published version

A well-known problem of the $��$CDM model is the tension between the relatively high level of clustering, as quantified by the parameter $��_8$, found in cosmic microwave background experiments and the smaller one obtained from large-scale observations in the late Universe. In this paper we show that coupled quintessence, i.e. a single dark energy scalar field conformally coupled to dark matter through a constant coupling, can solve this problem if the background is taken to be identical to the $��$CDM one. We show that two competing effects arise. On one hand, the additional scalar force is attractive, and is therefore expected to increase the clustering. On the other, in order to obtain the same background as $��$CDM, coupled quintessence must have a smaller amount of dark matter near the present epoch. We show that the second effect is dominating today and leads to an overall slower growth. Comparing to redshift distortion data, we find that coupled quintessence with $��$CDM background solves the tension between early and late clustering. We find for the coupling $��$ and for $��_8$ the best fit values $|��| = 0.079^{+ 0.059}_{- 0.067}$ and $��_8 = 0.818^{+0.115}_{-0.088}$. These values also fit the lensing data from the KiDS-450 survey. We also estimate that the future missions SKA and Euclid will constrain $��$ with an error of $\pm\, 1.5\times10^{-3}$ and for $��_8$ of $\pm \,1.8\times10^{-3}$ at $1��$ level., 8 pages, 6 figures. V2: Matches published version

Analyses of gamma-ray spectra, acquired through non-invasive techniques, have found applications in fields such as medicine, industry and homeland security. Constituent gamma-ray spectra of a chemical compound have been determined from its sole spectrum through a forward Monte Carlo simulation coupled with a least squares method (MCLLS). The method's limitations include its linearity assumption and its oversensitivity to correlated or noisy data, which render the method unfit to deal with such numerical ill conditioning. Recently this issue was tackled by iteratively reducing the condition number of the linear system of equations. Despite its superior results, it is not suitable for cases where there are missing libraries in the analysis. Our work introduces a novel framework that allows treating spectral analyses problems through geometrical insights. Based on this it was possible to propose solutions to three problems regarding the missing library: to find its photopeak, its most probable fraction, and an envelope around its spectrum. We successfully validated these on some Monte Carlo-generated radionuclide gamma-ray spectra.