36 research outputs found
Tachyacoustic Cosmology: An Alternative to Inflation
We consider an alternative to inflation for the generation of superhorizon
perturbations in the universe in which the speed of sound is faster than the
speed of light. We label such cosmologies, first proposed by Armendariz-Picon,
{\it tachyacoustic}, and explicitly construct examples of non-canonical
Lagrangians which have superluminal sound speed, but which are causally
self-consistent. Such models possess two horizons, a Hubble horizon and an
acoustic horizon, which have independent dynamics. Even in a decelerating
(non-inflationary) background, a nearly scale-invariant spectrum of
perturbations can be generated by quantum perturbations redshifted outside of a
shrinking acoustic horizon. The acoustic horizon can be large or even infinite
at early times, solving the cosmological horizon problem without inflation.
These models do not, however, dynamically solve the cosmological flatness
problem, which must be imposed as a boundary condition. Gravitational wave
modes, which are produced by quantum fluctuations exiting the Hubble horizon,
are not produced.Comment: 11 pages, LaTeX (V2: references added. Version submitted to PRD
CMB Polarization and Theories of Gravitation with Massive Gravitons
We study in this paper three different theories of gravitation with massive
gravitons - the modified Fierz-Pauli (FP) model, Massive Gravity and the
bimetric theory proposed by Visser - in linear perturbation theory around a
Minkowski and a flat FRW background. For the TT tensor perturbations we show
that the three theories give rise to the same dynamical equations and to the
same form of the Boltzmann equations for the radiative transfer in General
Relativity (GR). We then analyze vector perturbations in these theories and
show that they do not give the same results as in the previous case. We first
show that vector perturbations in Massive Gravity present the same form as
found in General Relativity, whereas in the modified FP theory the vector
gravitational-wave (GW) polarization modes ( amplitudes in the
Newman-Penrose (NP) formalism) do not decay too fast as it happens in the
former case. Rather, we show that such polarization modes give rise
to an unusual vector Sachs-Wolfe effect, leaving a signature in the quadrupole
form on the CMB polarization. We then derive the
details for the Thomson scattering of CMB photons for these modes,
and then construct the correspondent Boltzmann equations. Based upon these
results we then qualitatively show that -mode vector signatures - if
they do exist - could clearly be distinguished on the CMB polarization from the
usual tensor modes.Comment: To appear in Classical and Quantum Gravit
Solid-state 31P and 109Ag CP/MAS NMR as a powerful tool for studying of silver(I) complexes with N-thiophosphorylated thiourea and thioamide ligands
A family of three- and four-coordinated silver(I) complexes of formulas [Ag(PPh3)2L], [Ag(PPh3)L], and [AgL]n with N-thiophosphorylated thiourea and thioamide ligands of general formula RC(S)NHP(S)(OPri)2 [R = Ph, PhNH, iPrNH, tBuNH, NH2] have been studied by solid-state 109Ag and 31P CPMAS NMR spectroscopy. 109Ag NMR spectra have provided valuable structural information about Ag coordination, which is in good accordance with the available crystal structure data. The data presented in this work represent a significant addition to the available 109Ag chemical shifts and chemical shifts anisotropies. The silver chemical shift ranges for different P,S-environments and coordination state were discussed in detail. The 1J(31P–107/109Ag) and 2J(31P–31P) values were determined and analyzed. © 2022 John Wiley & Sons Ltd.Kazan Federal University: Priority-2030Financial support from the IR-RMN-THC Fr3050 CNRS for conducting the research is gratefully acknowledged. This paper has been supported by the Kazan Federal University Strategic Academic Leadership Program (Priority-2030).Financial support from the IR-RMN-THC Fr3050 CNRS for conducting the research is gratefully acknowledged. This paper has been supported by the Kazan Federal University Strategic Academic Leadership Program (Priority-2030)
Extra polarization states of cosmological gravitational waves in alternative theories of gravity
Cosmological Gravitational Waves (GWs) are usually associated with the
transverse-traceless part of the metric perturbations in the context of the
theory of cosmological perturbations. These modes are just the usual
polarizations `+' and `x' which appear in the general relativity theory.
However, in the majority of the alternative theories of gravity, GWs can
present more than these two polarization states. In this context, the
Newman-Penrose formalism is particularly suitable for evaluating the number of
non-null GW modes. In the present work we intend to take into account these
extra polarization states for cosmological GWs in alternative theories of
gravity. As an application, we derive the dynamical equations for cosmological
GWs for two specific theories, namely, a general scalar-tensor theory which
presents four polarization states and a massive bimetric theory which is in the
most general case with six polarization states for GWs. The mathematical tool
presented here is quite general, so it can be used to study cosmological
perturbations in all metric theories of gravity.Comment: 26 pages, 1 figure. Accepted for publication in Classical and Quantum
Gravity
Polymorphs of Rb3ScF6: X-ray and Neutron Diffraction, Solid-State NMR, and Density Functional Theory Calculations Study
The crystal structures of three polymorphs of Rb3ScF6 have been determined through a combination of synchrotron, laboratory X-ray, and neutron powder diffraction, electron diffraction, and multinuclear high-field solid-state NMR studies. The room temperature (RT; α) and medium-temperature (β) structures are tetragonal, with space groups I41/a (Z = 80) and I4/m (Z = 10) and lattice parameters a = 20.2561(4) Å, c = 36.5160(0) Å and a = 14.4093(2) Å, c = 9.2015(1) Å at RT and 187 °C, respectively. The high-temperature (γ) structure is cubic space group Fm3¯ m (Z = 4) with a = 9.1944(1) Å at 250 °C. The temperatures of the phase transitions were measured at 141 and 201 °C. The three α, β, and γRb3ScF6 phases are isostructural with the α, β, and δforms of the potassium cryolite. Detailed structural characterizations were performed by density functional theory as well as NMR. In the case of the β polymorph, the dynamic rotations of the ScF6 octahedra of both Sc crystallographic sites have been detailed. © 2021 American Chemical Society.For DFT calculations, we thank the “Centre de Calcul Scientifique en region Centre” (Orléans, France). We acknowledge the Interface, Confinement, Materials and Nanostructures (Orléans, France) for access to their transmission electron microscope. Financial support from the IR-RMN-THC Fr3050 CNRS for conducting the research is gratefully acknowledged. This study was also financially supported by VEGA-2/0060/18 and ITMS project (code 313021T081, Research & Innovation Operational Programme funded by the ERDF). We thank also Dr. F. Vivet, Dr. F. Fayon, and Dr. D. Massiot for useful discussions
Fabrication of magnetic and photocatalytic polyamide fabric coated with Fe2O3 particles
Hematite (alpha-Fe₂O₃) particles are prepared and synchronously deposited on the surface of polyamide (PA) fabric using ferric sulfate as the precursor, sodium hydroxide as the precipitant, and sodium dodecyl benzene sulfonate as the dispersant in a low temperature hydrothermal process. The Fe₂O₃ coated PA fabric is then modified with silane coupling agent Z-6040. The Fe₂O₃ coated PA fabric and remaining particles are systematically characterized by different techniques, such as small-spot micro X-ray fluorescence (μ-XRF), field-emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), diffuse reflectance spectrum (DRS), and vibrating sample magnetometer (VSM). The properties of tensile, durable washing and photocatalytic activity are investigated. The experimental results show that Fe₂O₃ particles composed of nanoparticles having the average crystallite size of 37.8 nm are grafted onto PA fabric and enhanced by coupling agent via the C-Fe, O-Fe and Si-O-Fe bonds. It is found that, after treatments, the thermal stability of PA fabric hardly changes; the visible light absorption capability and magnetism are gained; and the tensile property decreases slightly. It is also confirmed that the Fe₂O₃ coated PA fabric can withstand the repeated washings up to 20 times and photodegrade the adsorbed methyl orange (MO) exposed to ultraviolet (UV) irradiation. Therefore, the present method provides a new strategy for the production of durable magnetic fabric
Status Report Of The Schenberg Gravitational Wave Antenna
Here we present a status report of the Schenberg antenna. In the past three years it has gone to a radical upgrading operation, in which we have been installing a 1K pot dilution refrigerator, cabling and amplifiers for nine transducer circuits, designing a new suspension and vibration isolation system for the microstrip antennas, and developing a full set of new transducers, microstrip antennas, and oscillators. We are also studying an innovative approach, which could transform Schenberg into a broadband gravitational wave detector.3631Aguiar, O.D., (2002) Class. Quantum Grav., 19, p. 1949Aguiar, O.D., (2004) Class. Quantum Grav., 21, pp. S457Aguiar, O.D., (2005) Class. Quantum Grav., 22, pp. S209Aguiar, O.D., (2006) Class. Quantum Grav., 23, pp. S239Aguiar, O.D., (2008) Class. Quantum Grav., 25, p. 114042Costa, C.A., (2008) Class. Quantum Grav., 25, p. 184002Johnson, W.W., Merkowitz, S.M., (1993) Phys. Rev. Lett., 70, p. 2367Coccia, E., Lobo, J.A., Ortega, J.A., (1995) Phys. Rev. D, 52, p. 3735Thorne, K.S., (1978) Phys. Rev. Lett., 40, p. 667Tobar, M.E., Ivanov, E.N., Blair, D.G., (2000) Gen. Rel. Grav., 32, p. 1799De Waard, (2005) Class. Quantum Grav., 22, pp. S215Vinet, J.-Y., (2010) Research in Astron Astrophys., 10, p. 956Costa, C.A., Aguiar, O.D., Magalhães, N.S., (2004) Class. Quantum Grav., 21, pp. S827Forward, R.L., (1971) Gen. Rel. Grav., 2, p. 149Eardley, D.M., Lee, D.L., Lightman, A.P., Wagoner, R.V., Will, C.M., (1973) Phys. Rev. Lett., 30, p. 884Bianchi, M., Coccia, E., Colacino, C.N., Fafone, V., Fucito, F., (1996) Class. Quantum Grav., 13, p. 2865Andrade, L.A., (2009) Microwave and Optical Tech. Lett., 51, p. 1120Furtado, S.R., (2012), in preparationIvanov, E.N., Hartnett, J.G., Tobar, M.E., (2000) IEEE Trans. Ultrason., Ferroelect., Freq. Contr., 47, p. 1526Pimentel, G.L., (2008) J. Phys. Conf. Series, 122, p. 012028Aguiar, (2009) Int. J. Modern Phys. D, 18, p. 2317Furtado, S.R., (2009), Ph.D. Thesis at INPE, not publishedBraginsky, V.B., Vorontsov, Y.I., Thorne, K.S., (1980) Science, 209, p. 547Thorne, K.S., The Quantum Limit for Gravitational-Wave Detectors and Methods of Circumventing It (1979) Sources of Gravitational Waves, p. 49. , ed. L L Smarr, Cambridge University Press, Cambridge, US