2,188 research outputs found
Damping the neutrino flavor pendulum by breaking homogeneity
The most general case of self-induced neutrino flavor evolution is described
by a set of kinetic equations for a dense neutrino gas evolving both in space
and time. Solutions of these equations have been typically worked out assuming
that either the time (in the core-collapse supernova environment) or space (in
the early universe) homogeneity in the initial conditions is preserved through
the evolution. In these cases one can gauge away the homogeneous variable and
reduce the dimensionality of the problem. In this paper we investigate if small
deviations from an initial postulated homogeneity can be amplified by the
interacting neutrino gas, leading to a new flavor instability. To this end, we
consider a simple two flavor isotropic neutrino gas evolving in time, and
initially composed by only and with equal densities. In the
homogeneous case, this system shows a bimodal instability in the inverted mass
hierarchy scheme, leading to the well studied flavor pendulum behavior. This
would lead to periodic pair conversions . To break space homogeneity, we introduce small amplitude
space-dependent perturbations in the matter potential. By Fourier transforming
the equations of motion with respect to the space coordinate, we then
numerically solve a set of coupled equations for the different Fourier modes.
We find that even for arbitrarily tiny inhomogeneities, the system evolution
runs away from the stable pendulum behavior: the different modes are excited
and the space-averaged ensemble evolves towards flavor equilibrium. We finally
comment on the role of a time decaying neutrino background density in weakening
these results.Comment: (7 pages, 5 eps figures. Figure improved. Final version appeared in
PRD
Self-induced flavor instabilities of a dense neutrino stream in a two-dimensional model
We consider a simplifed model for self-induced flavor conversions of a dense
neutrino gas in two dimensions, showing new solutions that spontaneously break
the spatial symmetries of the initial conditions. As a result of the symmetry
breaking induced by the neutrino-neutrino interactions, the coherent behavior
of the neutrino gas becomes unstable. This instability produces large spatial
variations in the flavor content of the ensemble. Furthermore, it also leads to
the creation of domains of different net lepton number flux. The transition of
the neutrino gas from a coherent to incoherent behavior shows an intriguing
analogy with a streaming flow changing from laminar to turbulent regime. These
finding would be relevant for the self-induced conversions of neutrinos
streaming-off a supernova core.Comment: (v2: revised version: 8 pages, 7 eps figures. To appear on Physical
Review D as Rapid Communication. Discussion enlarged. Two Appendices added.
Unveiling secret interactions among sterile neutrinos with big-bang nucleosynthesis
Short-baseline neutrino anomalies suggest the existence of low-mass ( m \sim
O(1)~eV) sterile neutrinos \nu_s. These would be efficiently produced in the
early universe by oscillations with active neutrino species, leading to a
thermal population of the sterile states seemingly incompatible with
cosmological observations. In order to relieve this tension it has been
recently speculated that new "secret" interactions among sterile neutrinos,
mediated by a massive gauge boson X (with M_X << M_W), can inhibit or suppress
the sterile neutrino thermalization, due to the production of a large matter
potential term. We note however, that they also generate strong collisional
terms in the sterile neutrino sector that induce an efficient sterile neutrino
production after a resonance in matter is encountered, increasing their
contribution to the number of relativistic particle species N_ eff. Moreover,
for values of the parameters of the \nu_s-\nu_s interaction for which the
resonance takes place at temperature T\lesssim few MeV, significant distortions
are produced in the electron (anti)neutrino spectra, altering the abundance of
light element in Big Bang Nucleosynthesis (BBN). Using the present
determination of He and deuterium primordial abundances we determine the
BBN constraints on the model parameters. We find that H/H density ratio
exclude much of the parameter space if one assume a baryon density at the best
fit value of Planck experiment, \Omega_B h^2= 0.02207, while bounds become
weaker for a higher \Omega_B h^2=0.02261, the 95 % C.L. upper bound of Planck.
Due to the large error on its experimental determination, the helium mass
fraction Y_p gives no significant bounds.Comment: v2: revised version. Minor changes: figures improved, references
updated. Matches the version to appear in Phys. Rev.
Reconstruction of the 2018 Anak Krakatau collapse using PlanetScope imaging and numerical modeling
The study was focused on the Anak Krakatau sector collapse that occurred on 22 December 2018 in the Sunda Strait (Indonesia). The goal of the study was to monitor and analyze changes of the volcanic edifice and to try to understand causes that may have predisposed and triggered the sector collapse.
The use of different remote sensing techniques allowed the acquisition of thermal data, SO2 emission data, structural data and the identification and analysis of the eruptive events that occurred on Anak Krakatau in the period from 1° January 2016 to 28 February 2019. The acquisition of 1221 thermal data and 1156 SO2 emission data was performed using MODIS and OMI. Anak Krakatau began a new and intense activity phase on 30 June 2018 which continued in the following six months preceding the lateral collapse of the SW flank of the volcanic edifice, reaching its climax in September. The activity subsequently followed a decreasing trend, ending shortly after the collapse. The thermal data and the use of PlanetScope images allowed the identification of 8 lava flows, 7 of which developed between July and November 2018, exactly in the months that preceded the collapse. Almost all the lava flows affected the SW, S-SW and S slopes of the volcanic cone. These events led to an increase of the lithostatic load on the area subsequently collapsed. Precisely, their volume is equal to 6.8x106 m3. The volumes of all the lava flows were calculated considering an average thickness of 10m, obtaining a total volume equal to 8.2x106 m3. Further analysis of the satellite images highlighted a shift of the summit crater mainly towards the area subsequently collapsed and the generation of different curvilinear fractures which can be grouped in three main strikes’ groups: NW-SE; E-W and NNE-SSW. The structures with NW-SE strike agree with regional tectonics while those with E-W and NNE-SSW direction delimit the subsequent collapse. What has been observed indicates that there were precursory signs of structural instability. Finally, based on the collected data, bibliographic information regarding the extent of caldera-forming ignimbrite and deep surveys, it was possible to create the first pre-collapse 3D model representing the area present before the 2018 collapse. This model is a key element for a possible simulation of the sector collapse that occurred on Anak Krakatau.
The model allows to test three hypotheses of possible predisposing causes in future studies: 1) Increase of the lithostatic load on the SW side of the volcano generated by the deposition of all products erupted during the last phase of activity, considering also its high inclination (\u3e 20 °); 2) Dike intrusion into the shallow portion of the volcanic edifice; 3) External factors which are common predisposing causes that influence the stability of the volcanic slopes such as a failure plane, zones of weakness, hydrothermal activity and mechanical weakening by alteration.
The study shows that the collapse of Anak Krakatau could have been anticipated through continuous monitoring of the volcano and its activity using different remote sensing techniques. Finally, we believe that the combination of 3D models, representing areas with signs of instability, and remote sensing techniques is an important method for predicting potentially disastrous events, and Anak Krakatau is an example
Cosmogenic neutrino fluxes under the effect of active-sterile secret interactions
Ultra High Energy cosmogenic neutrinos may represent a unique opportunity to
unveil possible new physics interactions once restricted to the neutrino sector
only. In the present paper we study the observable effects of a secret
active-sterile interactions, mediated by a pseudoscalar, on the expected flux
of cosmogenic neutrinos. The results show that for masses of sterile neutrinos
and pseudoscalars of hundreds MeV, necessary to evade cosmological,
astrophysical and elementary particle constraints, the presence of such new
interactions can significantly change the energy spectrum of cosmogenic
neutrinos at Earth in the energy range from PeV to ZeV. Interestingly, the
distortion of the spectrum results to be detectable at GRAND apparatus if the
scalar mediator mass is around 250 MeV and the UHECRs are dominated by the
proton component. Larger mediator masses or a chemical composition of UHECRs
dominated by heavier nuclei would require much larger cosmic rays apparatus
which might be available in future.Comment: 10 pages, 3 figure
Curcumin-loaded zeolite as anticancer drug carrier: Effect of curcumin adsorption on zeolite structure
In this work we used a combination of different techniques to investigate the adsorption properties of curcumin by zeolite type A for potential use as an anticancer drug carrier. Curcumin is a natural water-insoluble drug that has attracted great attention in recent years due to its potential anticancer effect in suppressing many types of cancers, while showing a synergistic antitumor effect with other anticancer agents. However, curcumin is poorly soluble in aqueous solutions leading to the application of high drug dosage in oral formulations. Zeolites, inorganic crystalline aluminosilicates with porous structure on the nano- and micro-scale and high internal surface area, can be useful as pharmaceutical carrier systems to encapsulate drugs with intrinsic low aqueous solubility and improve their dissolution. Here, we explore the use of zeolite type A for encapsulation of curcumin, and we investigate its surface properties and morphology, before and after loading of the anticancer agent, using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and UV-vis spectroscopy. Results are used to assess the loading efficiency of zeolite type A towards curcumin and its structural stability after loading
Neutrinos in cosmology after Planck data
The Early Universe represents an important environment to test the neutrino proprieties. Indeed Big Bang Nucleosynthesis (BBN), baryogenesis, Cosmic Microwave Background (CMB) radiation, Large Scale Structure formation
(LSS) could be essentially influenced by the presence of neutrinos, in particular by their number and their mass. In recent years a renewed attention has been devoted to low-mass sterile neutrinos (m ∼ 1 eV), after intriguing but controversial hints coming from precision cosmological measurements and laboratory oscillation experiments. Given the doubtful situation, is necessary to study the physical conditions under which the sterile production occurs and to investigate the consequences on the cosmological observables
Cosmic microwave background constraints on secret interactions among sterile neutrinos
Secret contact interactions among eV sterile neutrinos, mediated by a massive
gauge boson (with ), and characterized by a gauge coupling
, have been proposed as a mean to reconcile cosmological observations and
short-baseline laboratory anomalies. We constrain this scenario using the
latest Planck data on Cosmic Microwave Background anisotropies, and
measurements of baryon acoustic oscillations (BAO). We consistently include the
effect of secret interactions on cosmological perturbations, namely the
increased density and pressure fluctuations in the neutrino fluid, and still
find a severe tension between the secret interaction framework and cosmology.
In fact, taking into account neutrino scattering via secret interactions, we
derive our own mass bound on sterile neutrinos and find (at 95% CL) eV or eV from Planck alone or in combination with BAO,
respectively. These limits confirm the discrepancy with the laboratory
anomalies. Moreover, we constrain, in the limit of contact interaction, the
effective strength to be from Planck
(Planck+BAO). This result, together with the mass bound, strongly disfavours
the region with MeV and relatively large coupling , previously indicated as a possible solution to the small scale dark
matter problem.Comment: 15 pages, 3 figures, 4 table
Multi-momentum and multi-flavour active-sterile neutrino oscillations in the early universe: role of neutrino asymmetries and effects on nucleosynthesis
We perform a study of the flavour evolution in the early universe of a
multi-flavour active-sterile neutrino system with parameters inspired by the
short-baseline neutrino anomalies. In a neutrino-symmetric bath a "thermal"
population of the sterile state would quickly grow, but in the presence of
primordial neutrino asymmetries a self-suppression as well as a resonant
sterile neutrino production can take place, depending on temperature and chosen
parameters. In order to characterize these effects, we go beyond the usual
average momentum and single mixing approximations and consider a multi-momentum
and multi-flavour treatment of the kinetic equations. We find that the
enhancement obtained in this case with respect to the average momentum
approximation is significant, up to \sim 20 % of a degree of freedom. Such
detailed and computationally demanding treatment further raises the asymmetry
values required to significantly suppress the sterile neutrino production, up
to large and preferentially net asymmetries |L_{\nu}| > O(10^{-2}). For such
asymmetries, however, the active-sterile flavour conversions happen so late
that significant distortions are produced in the electron (anti)neutrino
spectra. The larger |L_{\nu}|, the more the impact of these distortions takes
over as dominant cosmological effect, notably increasing the 4 He abundance in
primordial nucleosynthesis (BBN). The standard expression of the primordial
yields in terms of the effective number of neutrinos and asymmetries is also
greatly altered. We numerically estimate the magnitude of such effects for a
few representative cases and comment on possible implications for forthcoming
cosmological measurements.Comment: v2 (12 pages, 4 eps figures) revised version. Comments added,
references updated. Matches the version published in PR
The strongest bounds on active-sterile neutrino mixing after Planck data
Light sterile neutrinos can be excited by oscillations with active neutrinos
in the early universe. Their properties can be constrained by their
contribution as extra-radiation, parameterized in terms of the effective number
of neutrino species N_ eff, and to the universe energy density today \Omega_\nu
h^2. Both these parameters have been measured to quite a good precision by the
Planck satellite experiment. We use this result to update the bounds on the
parameter space of (3+1) sterile neutrino scenarios, with an active-sterile
neutrino mass squared splitting in the range (10^{-5} - 10^2 ) eV^2. We
consider both normal and inverted mass orderings for the active and sterile
states. For the first time we take into account the possibility of two
non-vanishing active-sterile mixing angles. We find that the bounds are more
stringent than those obtained in laboratory experiments. This leads to a strong
tension with the short-baseline hints of light sterile neutrinos. In order to
relieve this disagreement, modifications of the standard cosmological scenario,
e.g. large primordial neutrino asymmetries, are required.Comment: v2 (9 pages, 10 eps figures) revised version. Discussion enlarged.
Included bounds from the Planck limit on the sterile neutrino mass.
References update
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