Motohashi, H., & Starobinsky, A. A. (2017). f (R) constant-roll inflation. Eur. Phys. J. C, 77(8), 538–8pp.
Abstract: The previously introduced class of two-parametric phenomenological inflationary models in general relativity in which the slow-roll assumption is replaced by the more general, constant-roll condition is generalized to the case of f (R) gravity. A simple constant-roll condition is defined in the original Jordan frame, and exact expressions for a scalaron potential in the Einstein frame, for a function f (R) (in the parametric form) and for inflationary dynamics are obtained. The region of the model parameters permitted by the latest observational constraints on the scalar spectral index and the tensor-to-scalar ratio of primordial metric perturbations generated during inflation is determined.
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Motohashi, H., & Starobinsky, A. A. (2017). Constant-roll inflation: Confrontation with recent observational data. EPL, 117(3), 39001–3pp.
Abstract: The previously proposed class of phenomenological inflationary models in which the assumption of inflaton slow-roll is replaced by the more general, constant-roll condition is compared with the most recent cosmological observational data, mainly the Planck ones. Models in this two-parametric class which remain viable appear to be close to the slow-roll ones, and their inflaton potentials are close to (but still different from) that of the natural inflation model. The permitted regions for the two model parameters are presented.
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Motohashi, H., & Hu, W. (2017). Generalized slow roll in the unified effective field theory of inflation. Phys. Rev. D, 96(2), 023502–17pp.
Abstract: We provide a compact and unified treatment of power spectrum observables for the effective field theory (EFT) of inflation with the complete set of operators that lead to second-order equations of motion in metric perturbations in both space and time derivatives, including Horndeski and Gleyzes-Langlois-Piazza-Vernizzi theories. We relate the EFT operators in ADM form to the four additional free functions of time in the scalar and tensor equations. Using the generalized slow-roll formalism, we show that each power spectrum can be described by an integral over a single source that is a function of its respective sound horizon. With this correspondence, existing model independent constraints on the source function can be simply reinterpreted in the more general inflationary context. By expanding these sources around an optimized freeze-out epoch, we also provide characterizations of these spectra in terms of five slow-roll hierarchies whose leading-order forms are compact and accurate as long as EFT coefficients vary only on time scales greater than an e-fold. We also clarify the relationship between the unitary gauge observables employed in the EFT and the comoving gauge observables of the postinflationary universe.
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Motohashi, H., & Hu, W. (2017). Primordial black holes and slow-roll violation. Phys. Rev. D, 96(6), 063503–9pp.
Abstract: For primordial black holes (PBH) to be the dark matter in single-field inflation, the slow-roll approximation must be violated by at least O(1) in order to enhance the curvature power spectrum within the required number of e-folds between cosmic microwave background scales and PBH mass scales. Power spectrum predictions which rely on the inflaton remaining on the slow-roll attractor can fail dramatically leading to qualitatively incorrect conclusions in models like an inflection potential and misestimate the mass scale in a running mass model. We show that an optimized temporal evaluation of the Hubble slow-roll parameters to second order remains a good description for a wide range of PBH formation models where up to a 10(7) amplification of power occurs in 10 e-folds or more.
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Mostajeran, M., Sorolla, E., Rakova, E., & Gimeno, B. (2024). Space charge and two-sheet model in multipactor. Eur. Phys. J. Plus, 139(3), 256–13pp.
Abstract: The electron cloud populated by a multipactor within two emissive parallel plates was modeled by two thin sheets of charge, and for the first time the equations of the particle motion for this two-sheet system were derived taking into account space charge effects. The electron population growth in multipacting process was then simulated with the code developed on the base of these equations. It was found that the mutual repulsion between the sheets, i.e., space charge effects, results in the increasing of charge in one of the sheets and the loss of charge in the other due to the different growth rates. This process eventually comes to the saturation of one sheet and the dissappearence of the other.
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Mosbech, M. R., Boehm, C., Hannestad, S., Mena, O., Stadler, J., & Wong, Y. Y. Y. (2021). The full Boltzmann hierarchy for dark matter-massive neutrino interactions. J. Cosmol. Astropart. Phys., 03(3), 066–31pp.
Abstract: The impact of dark matter-neutrino interactions on the measurement of the cosmological parameters has been investigated in the past in the context of massless neutrinos exclusively. Here we revisit the role of a neutrino-dark matter coupling in light of ongoing cosmological tensions by implementing the full Boltzmann hierarchy for three massive neutrinos. Our tightest 95% CL upper limit on the strength of the interactions, parameterized via u(chi) = sigma(0)/sigma(Th) (m(chi)/100GeV)(-1), is u(chi) <= 3.34 . 10(-4), arising from a combination of Planck TTTEEE data, Planck lensing data and SDSS BAO data. This upper bound is, as expected, slightly higher than previous results for interacting massless neutrinos, due to the correction factor associated with neutrino masses. We find that these interactions significantly relax the lower bounds on the value of sigma 8 that is inferred in the context of Lambda CDM from the Planck data, leading to agreement within 1-2 sigma with weak lensing estimates of sigma 8, as those from KiDS1000. However, the presence of these interactions barely affects the value of the Hubble constant H-0.
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KM3NeT Collaboration(Adrian-Martinez, S. et al), Barrios-Marti, J., Calvo, D., Hernandez-Rey, J. J., Illuminati, G., Lotze, M., et al. (2017). Intrinsic limits on resolutions in muon- and electron-neutrino charged-current events in the KM3NeT/ORCA detector. J. High Energy Phys., 05(5), 008–39pp.
Abstract: Studying atmospheric neutrino oscillations in the few-GeV range with a multimegaton detector promises to determine the neutrino mass hierarchy. This is the main science goal pursued by the future KM3NeT/ORCA water Cherenkov detector in the Mediterranean Sea. In this paper, the processes that limit the obtainable resolution in both energy and direction in charged-current neutrino events in the ORCA detector are investigated. These processes include the composition of the hadronic fragmentation products, the subsequent particle propagation and the photon-sampling fraction of the detector. GEANT simulations of neutrino interactions in seawater produced by GENIE are used to study the effects in the 1-20 GeV range. It is found that fluctuations in the hadronic cascade in conjunction with the variation of the inelasticity y are most detrimental to the resolutions. The effect of limited photon sampling in the detector is of significantly less importance. These results will therefore also be applicable to similar detectors/media, such as those in ice.
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KM3NeT Collaboration(Aiello, S. et al), Barrios-Marti, J., Calvo, D., Coleiro, A., Colomer, M., Gozzini, S. R., et al. (2018). Characterisation of the Hamamatsu photomultipliers for the KM3NeT Neutrino Telescope. J. Instrum., 13, P05035–17pp.
Abstract: The Hamamatsu R12199-023-inch photomultiplier tube is the photodetector chosen for the first phase of the KM3NeT neutrino telescope. About 7000 photomultipliers have been characterised for dark count rate, timing spread and spurious pulses. The quantum efficiency, the gain and the peak-to-valley ratio have also been measured for a sub-sample in order to determine parameter values needed as input to numerical simulations of the detector.
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Moretti, F., Del Prete, M., & Montani, G. (2023). Linear analysis of the gravitational beam-plasma instability. Eur. Phys. J. C, 83(6), 486–16pp.
Abstract: We investigate the well-known phenomenon of the beam-plasma instability in the gravitational sector when a fast population of particles interacts with the massive scalar mode of a Horndeski theory of gravity, resulting in linear growth of the latter amplitude. Following the approach used in the standard electromagnetic case, we start from the dielectric representation of the gravitational plasma, as introduced in a previous analysis of the Landau damping for the scalar Horndeski mode. We then set up the modified Vlasov-Einstein equation, using a Dirac delta function to describe the fast beam distribution. We thus provide an analytical expression for the dispersion relation, and we demonstrate the existence of a nonzero growth rate for the linear evolution of the Horndeski scalar mode. A numerical investigation is then performed with a trapezoidal beam distribution function, which confirms the analytical results and allows us to demonstrate how the growth rate decreases as the beam spread increases.
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Moretti, F., Bombacigno, F., & Montani, G. (2020). Gravitational Landau damping for massive scalar modes. Eur. Phys. J. C, 80(12), 1203–9pp.
Abstract: We establish the possibility of Landau damping for gravitational scalar waves which propagate in a non-collisional gas of particles. In particular, under the hypothesis of homogeneity and isotropy, we describe the medium at the equilibrium with a Juttner-Maxwell distribution, and we analytically determine the damping rate from the Vlasov equation. We find that damping occurs only if the phase velocity of the wave is subluminal throughout the propagation within the medium. Finally, we investigate relativistic media in cosmological settings by adopting numerical techniques.
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