Derrick-type virial identities, obtained via dilatation (scaling) arguments, have a variety of applications in field theories. We deconstruct such virial identities in relativistic gravity showing how they can be reca...
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Derrick-type virial identities, obtained via dilatation (scaling) arguments, have a variety of applications in field theories. We deconstruct such virial identities in relativistic gravity showing how they can be recast as self-evident integrals of appropriate combinations of the equations of motion. In spherical symmetry, the appropriate combination and gauge choice guarantee the geometric part can be integrated out to yield a master form of the virial identity as a nontrivial energy-momentum balance condition, valid for both asymptotically flat black holes and self-gravitating solitons, for any matter model. Specifying the matter model we recover previous results obtained via the scaling procedure. We then discuss the more general case of stationary, axisymmetric, asymptotically flat black hole or solitonic solutions in general relativity, for which a master form for their virial identity is proposed, in a specific gauge but regardless of the matter content. In the flat spacetime limit, the master virial identity for both the spherical and axial cases reduces to a balance condition for the principal pressures, discussed by Deser.
Mixed fermion-boson stars are stable, horizonless, everywhere-regular solutions of the coupled Einstein-(complex, massive) Klein-Gordon-Euler system. While isolated neutron stars and boson stars are uniquely determine...
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Mixed fermion-boson stars are stable, horizonless, everywhere-regular solutions of the coupled Einstein-(complex, massive) Klein-Gordon-Euler system. While isolated neutron stars and boson stars are uniquely determined by their central energy density, mixed configurations conform to an extended parameter space that depends on the combination of the number of fermions and (ultralight) bosons. The wider possibilities offered by fermion-boson stars could help to explain the tension in the measurements of neutron star masses and radii reported in recent multimessenger observations and nuclear physics experiments. In this work, we construct equilibrium configurations of mixed fermion-boson stars with realistic equations of state for the fermionic component and different percentages of bosonic matter. We show that our solutions are in excellent agreement with multimessenger data, including gravitational-wave events GW170817 and GW190814 and x-ray pulsars PSR J0030+0451 and PSR J0740+6620, as well as with nuclear physics constraints from the PREX-2 experiment.
We construct and study rotating axion boson stars (RABSs). These are the spinning generalisations of the spherical gravitating solitons recently introduced in [1]. RABSs are asymptotically flat, stationary, axially sy...
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We investigate the effects ultralight bosonic field dark matter may have on the dynamics of unstable differentially rotating neutron stars prone to the bar-mode instability. To this aim we perform numerical simulation...
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We investigate the effects ultralight bosonic field dark matter may have on the dynamics of unstable differentially rotating neutron stars prone to the bar-mode instability. To this aim we perform numerical simulations in general relativity of rotating neutron stars accreting an initial spherically symmetric bosonic field cloud, solving the Einstein-(complex, massive) Klein-Gordon-Euler and the Einstein-(complex) Proca-Euler systems. We find that the presence of the bosonic field can critically modify the development of the bar-mode instability of neutron stars, depending on the total mass of the bosonic field and on the boson particle mass. In some cases, the accreting bosonic field can even quench the dominant ℓ=m=2 mode of the bar-deformation by dynamically forming a mixed (fermion-boson) star that retains part of the angular momentum of the original neutron star. However, the mixed star undergoes the development of a mixed bar that leads to significant gravitational-wave emission, substantially different to that of the isolated neutron star. Our results indicate that dark-matter accretion in neutron stars could change the frequency of the expected emission of the bar-mode instability, which would have an important impact on ongoing searches for continuous gravitational waves.
In this short paper, we obtain the eigenfunctions of the uniformly distributed-order wave equation in ℝn× ℝ+, as Laplace integral of Fox H-functions. For the particular case of the first fundamental solution, the...
In this short paper, we obtain the eigenfunctions of the uniformly distributed-order wave equation in ℝn× ℝ+, as Laplace integral of Fox H-functions. For the particular case of the first fundamental solution, the fractional moment of second order of the fundamental solution is studied using the Tauberian Theorem.
In this work, the eigenfunction problem for the time-fractional telegraph operator of distributed order in ℝn× ℝ+ is con-sidered. By employing the technique of the Fourier, Laplace and Mellin transforms, an integ...
In this work, the eigenfunction problem for the time-fractional telegraph operator of distributed order in ℝn× ℝ+ is con-sidered. By employing the technique of the Fourier, Laplace and Mellin transforms, an integral representation of the eigenfunctions involving the Fox H-function is obtained.
We study the impact of some abstract agent intervention on the disease spread modelled by a SIR-model with linear growth infectivity. The intervention is meant to decrease the infectivity, which are activated by a thr...
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Demand forecasting is one of the key aspects of operations management, particularly sales forecasting, as it plays a fundamental role in the retailer’s resource planning system, which impacts consumer satisfaction. T...
Demand forecasting is one of the key aspects of operations management, particularly sales forecasting, as it plays a fundamental role in the retailer’s resource planning system, which impacts consumer satisfaction. Traditional time series models are widely used in the context of sales forecasting, while machine learning approaches have been playing an important role in recent years. Different approaches should be tested and compared to support practical knowledge. In this work, we compare different prediction methods to forecast diesel fuel sales in a small business in order to choose the most suitable method, in terms of the usual evaluation measures, for presenting an inventory planning for weakly fuel sales.
Fundamentals of a function theory in co-dimension one for Clifford algebra valued functions over n+1 are considered. Special attention is given to their origins in analytic properties of holomorphic functions of one a...
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For a connected graph G on at least three vertices, the augmented Zagreb index (AZI) of G is defined as (Formula presented), being a topological index well-correlated with the formation heat of heptanes and octanes. A...
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