New actions for modified gravity and supergravity

We extend the f (R) gravity action by including a generic dependence upon the Weyl tensor, and further generalize it to supergravity by using the super-curvature R and super-Weyl W chiral superfields in N = 1 chiral curved superspace. We argue that our (super)gravitational actions are the meaningful extensions of the phenomenological f(R) gravity and its locally supersymmetric generalization towards their UV completion and their embedding into superstring theories. The proposed actions can be used for study of cosmological perturbations and gravitational instabilities due to a nonvanishing Weyl tensor in gravity and supergravity

On the superstring-inspired quantum correction to the Starobinsky model of inflation

Superstring/M-theory is the theory of quantum gravity that can provide the UV-completion to viable inflation models. We modify the Starobinsky inflation model by adding the Bel-Robinson tensor $T^{\mu\nu\lambda\rho}$ squared term proposed as the leading quantum correction inspired by superstring theory. The $(R+\frac{1}{6m^2}R^2 -\frac{\beta}{8m^6}T^2)$ model under consideration has two parameters: the inflaton mass $m$ and the string-inspired positive parameter $\beta$. We derive the equations of motion in the Friedmann-Lemaitre-Robertson-Walker universe and investigate its solutions. We find the physical bounds on the value of the parameter $\beta$ by demanding the absence of ghosts and consistency of the derived inflationary observables with the measurements of the cosmic microwave background radiation.Comment: 22 pages, 5 figures, LaTe

Analytic extensions of Starobinsky model of inflation

We study several extensions of the Starobinsky model of inflation, which obey all observational constraints on the inflationary parameters, by demanding that both the inflaton scalar potential in the Einstein frame and the F(R) gravity function in the Jordan frame have the explicit dependence upon fields and parameters in terms of elementary functions. Our models are continuously connected to the original Starobinsky model via changing the parameters. We modify the Starobinsky (R + R 2) model by adding an R 3-term, an R 4-term, and an R 3/2-term, respectively, and calculate the scalar potentials, the inflationary observables and the allowed limits on the deformation parameters by using the latest observational bounds. We find that the tensor-to-scalar ratio in the Starobinsky model modified by the R 3/2-term significantly increases with raising the parameter in front of that term. On the other side, we deform the scalar potential of the Starobinsky model in the Einstein frame in powers of y = exp(-(2/3)φ/M Pl), where φ is the canonical inflaton (scalaron) field, calculate the corresponding F(R) gravity functions in the two new cases, and find the restrictions on the deformation parameters in the lowest orders with respect to the variable y that is physically small during slow-roll inflation

On the Prospects of Using Metallic Glasses for In-vessel Mirrors for Plasma Diagnostics in ITER

This chapter reviews main results obtained on mirror-like samples made of several grades of bulk metallic glasses (BMG). Experiments were carried out under simulated conditions typical for the operation of plasma facing in-vessel mirrors of optical plasma diagnostics in fusion reactor ITER. Bombardment with D0 and T0 atoms radiated from burning plasma was predicted to be the main reason for the degradation of optical properties of such mirrors. Therefore, to simulate the behavior of mirrors in ITER, mirror-like samples were subjected to bombardment by ions of deuterium plasma with fixed or wide energy distribution. The effects of ion bombardment on optical properties, development of roughness, uptake of deuterium, appearance of blisters, and manifestation of some chemical processes are presented and discussed

Extending Starobinsky inflationary model in gravity and supergravity

International audienceWe review some recent trends in the inflationary model building, the super-symmetry (SUSY) breaking, the gravitino Dark Matter (DM) and the PrimordialBlack Holes (PBHs) production in supergravity. The Starobinsky inflation can beembedded into supergravity when the inflaton belongs to the massive vectormultiplet associated with a (spontaneously broken) U(1) gauge symmetry. The SUSYand R-symmetry can be also spontaneously broken after inflation by the(standard) Polonyi mechanism. Polonyi particles and gravitinos are super heavyand can be copiously produced during inflation via the Schwinger mechanismsourced by the Universe expansion. The overproduction and instability problemscan be avoided, and the positive cosmological constant (dark energy) can also beintroduced. The observed abundance of the Cold Dark Matter (CDM) composed ofgravitinos can be achieved in our supergravity model too, thus providing theunifying framework for inflation, supersymmetry breaking, dark energy and darkmatter genesis. Our supergravity approach may also lead to a formation ofprimordial non-linear structures like stellar-mass-type black holes, and mayinclude the SUSY GUTs inspired by heterotic string compactifications, unifyingparticle physics with quantum gravity. Povzetek. Avtorja obravnavata nekajnovejših modelov inflacije, zlomitve supersimetrije, temne snovi, ki josestavljajo gravitini in nastajanja prvotnihčrnih lukenj v supergravitaciji.Inflacija Starobinskega se pojavi v supergravitaciji , ˇ ce je inflaton delmasivnega vektorskga multipleta, ki spontano zlomi umeritveno simetrijo U(1).Supersimetrijo in simetrijo R lahko po inflaciji spontano zlomi tudi mehanizemPolonyija. Izredno masivni delci Polony-ija in gravitini, lahko nastanejovdovolj velikih koločinah med inflacijo z mehanizmom Schwingerja. S tem seavtorja izogneta problemu prevelike produkcije težkih delcev in nestabilnostiter pojasnita tudi pozitivno kozmološko konstanto (temno energijo). Njun model ssupergravitacijo razloži opaženo pogostost hladne temne snovi (CDM), ˇ ce joses-tavljajo gravitini in ponudi razlago za nastanek in potek inflacije,zlomitev supersimetrije, temno energijo in temno snov. Njun model lahko pojasnitudi nastanek prvotnih nelin-eranih struktur, kot sočrne luknje, ki imajo masoenake masi običajnih zvezd, in mord

Direct Formation of Hard-Magnetic Tetrataenite in Bulk Alloy Castings.

Funder: European Research Council; Id: http://dx.doi.org/10.13039/501100000781Currently, predominant high-performance permanent magnets contain rare-earth elements. In the search for rare-earth-free alternates, body-centered tetragonal Fe-Ni is notable. The ordering to form this phase from the usual cubic close-packed Fe-Ni is understood to be possible only below a critical temperature, commonly accepted to be 593 K. The ordering is first demonstrated by using neutron irradiation to accelerate atomic diffusion. The tetragonal phase, designated as the mineral tetrataenite, is found in Fe-based meteorites, its formation attributed to ultra-slow cooling. Despite many attempts with diverse approaches, bulk synthesis of tetrataenite has not been reported. Here it is shown that with appropriate alloy compositions, bulk synthesis of tetrataenite is possible, even in conventional casting at cooling rates 11-15 orders of magnitude higher than in meteorites. The barrier to obtaining tetrataenite (slow ordering from cubic close-packed to body-centered tetragonal) is circumvented, opening a processing window for potential rare-earth-free permanent magnets. The formation of tetrataenite on industrially practicable timescales also throws into question the interpretation of its formation in meteorites and their associated cooling rates

Formation of nanostructured metallic glass thin films upon sputtering

Morphology evolution of the multicomponent metallic glass film obtained by radio frequency (RF) magnetron sputtering was investigated in the present work. Two modes of metallic glass sputtering were distinguished: smooth film mode and clustered film mode. The sputtering parameters, which have the most influence on the sputtering modes, were determined. As a result, amorphous Ni-Nb thin films with a smooth surface and nanoglassy structure were deposited on silica float glass and Si substrates. The phase composition of the target appeared to have a significant influence on the chemical composition of the deposited amorphous thin film. The differences in charge transport and nanomechanical properties between the smooth and nanoglassy Ni-Nb film were also determined

Novel α + β Type Ti-Fe-Cu Alloys Containing Sn with Pertinent Mechanical Properties

Rising demand for bone implants has led to the focus on future alternatives of alloys with better biocompatibility and mechanical strength. Thus, this research is dedicated to the synthesis and investigation of new compositions for low-alloyed Ti-based compounds, which conjoin relatively acceptable mechanical properties and low elastic moduli. In this regard, the structural and mechanical properties of α + β Ti-Fe-Cu-Sn alloys are described in the present paper. The alloys were fabricated by arc-melting and tilt-casting techniques which followed subsequent thermo-mechanical treatment aided by dual-axial forging and rolling procedures. The effect of the concentrations of the alloying elements, and other parameters, such as regimes of rolling and dual-axial forging operation, on the microstructure and mechanical properties were thoroughly investigated. The Ti94Fe1Cu1Sn4 alloy with the most promising mechanical properties was subjected to thermo-mechanical treatment. After a single rolling procedure at 750 °C, the alloy exhibited tensile strength and tensile plasticity of 1300 MPa and 6%, respectively, with an elastic modulus of 70 GPa. Such good tensile mechanical properties are explained by the optimal volume fraction balance between α and β phases and the texture alignment obtained, providing superior alternatives in comparison to pure α- titanium alloys

Investigation of transparent magnetic material formed by selective oxidation of a metallic glass

We report on the formation of a transparent magnetic material containing nanocrystalline face-centered cubic (FCC) Ni produced by selective oxidation of Ni62Nb38 glassy alloy. Our results demonstrate the formation mechanism and provide the detailed structural characterization of the samples obtained. The proposed oxidation de-alloying method provides a simple way of producing samples containing fine nanocrystalline FCC Ni (average size ~ 3 nm) particles homogeneously distributed in an amorphous Nb2O5 matrix which is applicable as a magneto-optic material