Baryon Asymmetry and Gravitational Waves from Pseudoscalar Inflation

In models of inflation driven by an axion-like pseudoscalar field, the inflaton, a, may couple to the standard model hypercharge via a Chern-Simons-type interaction, $L \subset a/(4\Lambda) F\tilde{F}$. This coupling results in explosive gauge field production during inflation, especially at its last stage, which has interesting phenomenological consequences: For one thing, the primordial hypermagnetic field is maximally helical. It is thus capable of sourcing the generation of nonzero baryon number, via the standard model chiral anomaly, around the time of electroweak symmetry breaking. For another thing, the gauge field production during inflation feeds back into the primordial tensor power spectrum, leaving an imprint in the stochastic background of gravitational waves (GWs). In this paper, we focus on the correlation between these two phenomena. Working in the approximation of instant reheating, we (1) update the investigation of baryogenesis via hypermagnetic fields from pseudoscalar inflation and (2) examine the corresponding implications for the GW spectrum. We find that successful baryogenesis requires a suppression scale Lambda of around Lambda ~ 3 x 10^17 GeV, which corresponds to a relatively weakly coupled axion. The gauge field production at the end of inflation is then typically accompanied by a peak in the GW spectrum at frequencies in the MHz range or above. The detection of such a peak is out of reach of present-day technology; but in the future, it may serve as a smoking-gun signal for baryogenesis from pseudoscalar inflation. Conversely, models that do yield an observable GW signal suffer from the overproduction of baryon number, unless the reheating temperature is lower than the electroweak scale.Comment: 37 pages + references, 9 figures, 1 tabl

Enhanced visible-light-induced photocatalytic activity of α-Fe2O3 adsorbing redox enzymes

AbstractWe report fabrication of hybrid photocatalyst composed of an n-type semiconductor (α-Fe2O3) and a redox enzyme (horseradish peroxidase; HRP), and its performance for oxidation of luminol in an aqueous solution. The hybrid photocatalyst is simply formed via physical adsorption of HRP to an α-Fe2O3 sintered body. Under visible light irradiation, the bare α-Fe2O3 with a narrow bandgap photocatalytically oxidizes luminol along with blue emission that can be used as an indicator of the photocatalytic performance. The blue emission is largely strengthened after the adsorption of HRP, demonstrating that the presence of enzyme improves apparent photocatalytic activity of α-Fe2O3. The favorable effect is derived from synergistic oxidation of luminol by the biocatalysts (HRP) as well as by the photocatalyst (α-Fe2O3). In this paper, influence of excitation wavelength, adsorption amount of HRP, and reaction temperature on the overall photocatalytic activity are elucidated, and then a reaction mechanism of the proposed novel hybrid photocatalyst is discussed in detail

A new constraint on primordial lepton flavour asymmetries

A chiral chemical potential present in the early universe can source helical hypermagnetic fields through the chiral plasma instability. If these hypermagnetic fields survive until the electroweak phase transition, they source a contribution to the baryon asymmetry of the universe. In this letter, we demonstrate that lepton flavour asymmetries above $|\mu|/T \sim 9 \times 10^{-3}$ trigger this mechanism even for vanishing total lepton number. This excludes the possibility of such large lepton flavour asymmetries present at temperatures above $10^6$ GeV, setting a constraint which is about two orders of magnitude stronger than the current CMB and BBN limits.Comment: 4 pages, matches journal versio

Chiral magnetohydrodynamics with zero total chirality

We study the evolution of magnetic fields coupled with chiral fermion asymmetry in the framework of chiral magnetohydrodynamics with zero initial total chirality. The initial magnetic field has a turbulent spectrum peaking at a certain characteristic scale and is fully helical with positive helicity. The initial chiral chemical potential is spatially uniform and negative. We consider two opposite cases where the ratio of the length scale of the chiral plasma instability (CPI) to the characteristic scale of the turbulence is smaller and larger than unity. These initial conditions might be realized in cosmological models such as certain types of axion inflation. The magnetic field and chiral chemical potential evolve with inverse cascading in such a way that the magnetic helicity and chirality cancel each other at all times. The CPI time scale is found to determine mainly the time when the magnetic helicity spectrum attains negative values at high wave numbers. The turnover time of the energy-carrying eddies, on the other hand, determines the time when the peak of the spectrum starts to shift to smaller wave numbers via an inverse cascade. The onset of helicity decay is determined by the time when the chiral magnetic effect becomes efficient at the peak of the initial magnetic energy spectrum. When spin flipping is important, the chiral chemical potential vanishes and the magnetic helicity becomes constant, which leads to a faster increase of the correlation length, as expected from magnetic helicity conservation. This also happens when the initial total chirality is imbalanced. Our findings have important implications for baryogenesis after axion inflation.Comment: 21 pages, 20 figures, 4 table

Optimization of electrochemical synthesis conditions for dense and doped ceria thin films

In the present study, the appropriate electrolysis conditions were determined for attaining doped ceria thin films with a high density and adhesion in an aqueous solution containing of Ce3+ and Sm3+ ions. Based on a comparison of the anodic and cathodic polarizations, while the former only induced the deposition of Ce3+, the latter accomplished the simultaneous deposition of Ce and Sm species. Under an applied cathodic bias below the hydrogen evolution potential, the Ce3+ and Sm3+ were reacted with OH- ions generated by the reduction of water molecules, and then were deposited on the electrode as a hydroxide. The hydroxide was subsequently oxidized and dehydrated to form the ceria-based thin layer. The morphologies of the as-deposited films were significantly altered on the basis of the applied potential. Moreover, the addition of acetic acid to the electrolysis bath caused the production of a transparent, dense, and adherent film. The XRD pattern and Raman spectrum of the thin film revealed that the film was crystallized as the fluorite structure without any heat treatment, and Sm3+ is substituted at the Ce4+ site. Moreover, the Sm content in the film could be easily controlled by the metal concentration in the solution

Enhanced catalytic activity of enzymes interacting with nanometric titanate nanosheets

The effect of the coexistence of titanate nanosheets (TNS) with nanometric lateral dimensions (ca. 3 nm), which were prepared through a hydrolysis reaction of titanium tetraisopropoxide, on the catalytic activity of horseradish peroxidase (HRP) was investigated as a function of solution pH. Especially in diluted HRP solutions with a pH range of 7-8, enzymatic reaction rate, i.e. maximum velocity (Vmax), in the conventional Michaelis-Menten equation, was significantly enhanced more than 2 times in the presence of TNS. In contrast, the increase in Vmax was not very large in acidic (pH = 4.0) and basic solutions (pH = 9.0). It was demonstrated that the TNS brought about peptization of aggregates composed of several HRP molecules in a diluted solution, causing an increase in the apparent HRP concentration participating in the enzymatic reaction. Moreover, the TNS activated superoxide dismutase (SOD) with O2 - scavenging performance

YoeB-ribosome structure: a canonical RNase that requires the ribosome for its specific activity

As a typical endoribonuclease, YoeB mediates cellular adaptation in diverse bacteria by degrading mRNAs on its activation. Although the catalytic core of YoeB is thought to be identical to well-studied nucleases, this enzyme specifically targets mRNA substrates that are associated with ribosomes in vivo. However, the molecular mechanism of mRNA recognition and cleavage by YoeB, and the requirement of ribosome for its optimal activity, largely remain elusive. Here, we report the structure of YoeB bound to 70S ribosome in pre-cleavage state, revealing that both the 30S and 50S subunits participate in YoeB binding. The mRNA is recognized by the catalytic core of YoeB, of which the general base/acid (Glu46/His83) are within hydrogen-bonding distance to their reaction atoms, demonstrating an active conformation of YoeB on ribosome. Also, the mRNA orientation involves the universally conserved A1493 and G530 of 16S rRNA. In addition, mass spectrometry data indicated that YoeB cleaves mRNA following the second position at the A-site codon, resulting in a final product with a 3′-phosphate at the newly formed 3′ end. Our results demonstrate a classical acid-base catalysis for YoeB-mediated RNA hydrolysis and provide insight into how the ribosome is essential for its specific activit

Surface micromachining via solid electrochemical reaction on oxide ion conductors

We propose a simple and novel route for the surface microstructuring of tough materials (glassy carbon, SiC, W and Mo) through a solid electrochemical reaction at a microcontact between the oxide ion conductor and target substrate. More specifically, the surface of materials was locally oxidized by an anodic electrochemical reaction with the oxide ion conductor via the microcontact under a dc bias. Since the oxidation products of the targets were gaseous or sublimable, a fine-patterned surface was obtained as a result of the continuous consumption of the oxidation products formed at the microcontact. The success of the proposed method may stimulate such conventional applications of oxide ion conductors

Semiconductor-type SnO2-based NO2 sensors operated at room temperature under UV-light irradiation

NO2-sensing properties of typical oxide (SnO2, In2O3, or WO3)-based semiconductor gas sensors were measured at 30 °C with and without UV-light irradiation (main wavelength: 365 nm), and effects of noble-metal (Pd or Pt) loading, UV-light intensity (0?134 mW cm?2) and relative humidity in target gas (0?80%RH) on their NO2-sensing properties were investigated in this study. The UV-light irradiation effectively reduced the resistances of all sensors, enhanced their NO2 responses in some cases, and tended to accelerate their response and recovery speeds in dry air, because the UV-light irradiation promoted the adsorption and desorption of NO2-species on the surface. The SnO2 sensor showed the largest NO2 response in dry air, among all the pristine oxide sensors, especially under weak UV-light irradiation (?35 mW cm?2), together with relatively fast response and recovery speeds. The Pd or Pt loading onto SnO2 enhanced the NO2 response of the SnO2 sensor and accelerated their response and recovery speeds in dry air, while XPS analysis indicated that most of the Pd and Pt nanoparticles loaded on the surface were oxidized after heat treatment at 500 °C. Among all the sensors, the 0.05 wt% Pd-loaded SnO2 sensor showed the largest NO2 response under weak UV-light irradiation (?35 mW cm?2), together with relatively fast response and recovery speeds. The addition of moisture to the target gas had adverse effects on the NO2 responses and the response speeds of the SnO2 and 0.05 wt% Pd-loaded SnO2 sensors, but the weak UV-light irradiation (7 mW cm?2) largely reduced the dependence of the NO2 response of the 0.05Pd/SnO2 sensor on relative humidity while maintaining the large NO2 response, probably because the weak UV-light irradiation promotes the desorption of physisorbed water molecules and then the effective adsorption of NO2 on the 0.05Pd/SnO2 surface