Search Results (12)

Human exploration of the solar system will expose crew members to galactic cosmic radiation (GCR), with a potential for adverse health effects. GCR particles (protons and ions) move at nearly the speed of light and easily penetrate space station walls, as well as the human body. Previously, we have shown reactivation of latent herpesviruses, including herpes simplex virus, Varicella zoster virus, Epstein–Barr virus, and cytomegalovirus (CMV), during stays at the International Space Station. Given the prevalence of latent CMV and the known propensity of space radiation to cause alterations in many cellular processes, we undertook this study to understand the role of GCR in reactivating latent CMV. Latently infected Kasumi cells with CMV were irradiated with ¹³⁷Cs gamma rays, 150 MeV protons, 600 MeV/n carbon ions, 600 MeV/n iron ions, proton ions, and simulated GCR. The CMV copy number increased significantly in the cells exposed to radiation as compared with the non-irradiated controls. Viral genome sequencing did not reveal significant nucleotide differences among the compared groups. However, transcriptome analysis showed the upregulation of transcription of the UL49 ORF, implicating it in the switch from latent to lytic replication. These findings support our hypothesis that GCR may be a strong contributor to the reactivation of CMV infection seen in ISS crew members. Full article

We consider the discrete $Z_4$ symmetry $\widehat{\mathbf{i}}$, which takes place in the scenario of quantum gravity where the gravitational tetrads emerge as the order parameter—the vacuum expectation value of the bilinear combination of fermionic operators. Under this symmetry operation, $\widehat{\mathbf{i}}$, the emerging tetrads are multiplied by the imaginary unit, $\widehat{\mathbf{i}}{e}_{\mu }^a=-i{e}_{\mu }^a$. The existence of such symmetry and the spontaneous breaking of this symmetry are also supported by the consideration of the symmetry breaking scheme in the topological superfluid ³He-B. The order parameter in ³He-B is also the bilinear combination of the fermionic operators. This order parameter is the analog of the tetrad field, but it has complex values. The $\widehat{\mathbf{i}}$-symmetry operation changes the phase of the complex order parameter by $\pi /2$, which corresponds to the $Z_4$ discrete symmetry in quantum gravity. We also considered the alternative scenario of the breaking of this $Z_4$ symmetry, in which the $\widehat{\mathbf{i}}$-operation changes sign of the scalar curvature, $\widehat{\mathbf{i}}\mathcal{R}=-\mathcal{R}$, and thus the Einstein–Hilbert action violates the $\widehat{\mathbf{i}}$-symmetry. In the alternative scenario of symmetry breaking, the gravitational coupling $K=1/16\pi G$ plays the role of the order parameter, which changes sign under $\widehat{\mathbf{i}}$-transformation. Full article

AliCPT-1 is the first cosmic microwave background (CMB) experiment in China dedicated to achieving accurate measurements of B-mode polarization. Situated in Ali of Tibet, China, this telescope is currently undergoing deployment and will operate in two frequency bands centered at 90 and 150 GHz. The far-field flat mirror (FFF) is a calibration device of the AliCPT-1 telescope for far-field beam mapping. The design of the FFF is optimized for easy assembly and adjustment. Meteorological station data reveal that the maximum wind speed near the FFF is 17.5 m/s, while the maximum wind speed on the windward side is 8 m/s. The wind pressure on the FFF was analyzed using a maximum wind speed of 17.5 m/s as the input condition, based on the fluid–structure coupling method in ANSYS. The results demonstrate that it is safe and reliable when withstanding combined gravity and wind pressure loads. The torque on the mount is within the motor rated torque. The flatness of the FFF reflective surface can be adjusted to an RMS value of 0.05 mm when taking into account the effect of gravity and assembly accuracy. The deformation caused by the maximum wind loads is approximately 0.0587 mm under the protection of the wind-proof wall. The combined deformation is 0.077 mm in RMS value combining the two influences, which is less than 1/20 of wavelength. The FFF mirror assembly is stable and precise for telescope calibration. Full article

The ALPHA-g experiment at CERN intends to observe the effect of gravity on antihydrogen. In ALPHA-g, antihydrogen is confined to a magnetic trap with an axis aligned parallel to the Earth’s gravitational field. An imposed difference in the magnetic field of the confining coils above and below the trapping region, known as a bias, can be delicately adjusted to compensate for the gravitational potential experienced by the trapped anti-atoms. With the bias maintained, the magnetic fields of the coils can be ramped down slowly compared to the anti-atom motion; this releases the antihydrogen and leads to annihilations on the walls of the apparatus, which are detected by a position-sensitive detector. If the bias cancels out the gravitational potential, antihydrogen will escape the trap upwards or downwards with equal probability. Determining the downward (or upward) escape probability, p, from observed annihilations is non-trivial because the annihilation detection efficiency may be up–down asymmetric; some small fraction of antihydrogen escaping downwards may be detected in the upper region (and vice versa) meaning that the precise number of trapped antihydrogen atoms is unknown. In addition, cosmic rays passing through the apparatus lead to a background annihilation rate, which may also be up–down asymmetric. We present a Bayesian method to determine p by assuming annihilations detected in the upper and lower regions are independently Poisson distributed, with the Poisson mean expressed in terms of experimental quantities. We solve for the posterior p using the Markov chain Monte Carlo integration package, Stan. Further, we present a method to determine the gravitational acceleration of antihydrogen, $a_g$, by modifying the analysis described above to include simulation results. In the modified analysis, p is replaced by the simulated probability of downward escape, which is a function of $a_g$. Full article

As humanity prepares for extended lunar exploration, understanding the radiation environment on the Moon is important for astronaut safety. This study utilized the Particle and Heavy-Ion Transport code System (PHITS), a stochastic Monte Carlo-based radiation transport code, to simulate the radiation environment inside a habitat, focusing on the impact of galactic cosmic rays (GCRs) interacting with local lunar and habitat material, and to calculate the effective dose equivalent. Placing a lunar base in a crater can provide additional shielding by reducing the GCR flux incident on the base. Furthermore, the secondary radiation field created by GCR interactions may be altered by the local topological features. GCR transport calculations were performed for a hypothetical base on a flat surface and in shallow and deep craters to determine the overall efficacy in dose reduction gained by placing a base in a 100 m diameter crater. Our findings indicate that the depth of lunar habitats significantly influences the effective dose equivalent, with deeper locations offering substantial protection. Specifically, alongside a crater wall at a deep depth (15 m), in solar minimum conditions, the total dose was reduced by approximately 44.9% compared to the dose at the surface. Similarly, at a shallow depth (5 m), a reduction of approximately 10.7% was observed. As the depth of the crater increased, the neutron contribution to the total dose also increased. Comparing the simulated doses to NASA’s lifetime exposure limits provides insights into mission planning and astronaut safety, emphasizing the importance of strategic habitat placement and design. Full article

In this paper, we study the dynamical and statistical properties of the cosmic web and investigate their ability to infer the corresponding cosmological model. Our definition of the cosmic web is based on the local dimensionality of the gravitational collapse that classifies the cosmic web into four categories: voids, walls, filaments, and nodes. Our results show that each category has its specific non-Gaussian evolution over time and that these non-Gaussianities depend on the cosmological parameters. Nonetheless, the non-Gaussianities in each category exist even at early epochs when the matter field has a Gaussian distribution. Additionally, by using deep learning techniques, we show that leveraging the cosmic web information engenders an improved inference of cosmological parameters, when compared to merely using the matter field. Full article

Spacetime torsion is known to be highly suppressed at the end of inflation, which is called preheating. This result was recently shown in (EPJ C (2022)) in the frame of Einstein–Cartan–Brans–Dicke inflation. In this paper, it is shown that a torsionful magnetogenesis in QED effective Lagrangean drives a torsion damping in order to be subsequently amplified by the dynamo effect after the generation of these magnetic fields seeds. This damping on amplification would depend upon the so-called torsion chirality. Here, a cosmic factor $gkK$ is present where K is the contortion vector and k is the wave vector which is connected to the inverse of magnetic coherence length. In a second example, we find Higgs inlationary fields in Einstein–Cartan gravity thick domain walls (DWs). Recently, a modified Einstein–Cartan gravity was given by Shaposhnikov et al. [PRL (2020)] to obtain Higgs-like inflatons as a portal to dark energy. In the case of thick DW, we assume that there is a torsion squared influence, since we are in the early universe where torsion is not so weak as in the late universe as shown by Paul and SenGupta [EPJ C (2019)] in a 5D brane-world. A static DW solution is obtained when the inflationary potential vanishes and Higgs potential is a helical function. Recently, in the absence of inflation, domain wall dynamos were obtained in Einstein–Cartan gravity (EC) where the spins of the nucleons were orthogonal to the wall. Full article

Both the lack of observation of ultra-high energy (UHE) photons and the limitations of the state-of-the-art methodology being applied for their identification motivate studies on alternative approaches to the relevant simulations and the related observational strategies. One such new approach is proposed in this report and it concerns new observables allowing indirect identification of UHE photons through cosmic ray phenomena composed of many spatially correlated extensive air showers or primary cosmic rays observed at one time. The study is based on simulations of interactions of UHE photons with the magnetic field of the Sun using the PRESHOWER program with some essential modifications. One of the expected results of such interactions is a generation of cosmic ray ensembles (CREs) in the form of very thin and very elongated cascades of secondary photons of energies spanning the whole cosmic ray energy spectrum. Upon entering the Earth’s atmosphere, these cascades or their parts may generate uniquely characteristic walls of spatially correlated extensive air showers, and the effect is expected also in cases when primary UHE photons are not directed towards the Earth. Particle distributions in these multi-primary UHE photon footprints are expected to have thicknesses of the order of meters and elongations reaching even hundreds of millions of kilometers, making them potentially observable with a global, multi-experiment approach, including re-exploring of the historical data, with the expected event rate exceeding the capabilities of even very large cosmic ray observatories. In this report, we introduce for the first time the methods allowing for simulating the isotropic flux of UHE photons in the Sun’s vicinity. Presented methods were verified and optimised in such a way that they would successfully model the cumulative spatial distribution of secondary photons at the top of the atmosphere. The preliminary results of simulations for the UHE photon flux of energy 100 EeV demonstrate the possibility of simulating potentially observable quantities related to CRE induced by UHE photons: densities, energy spectra and geographical orientations of secondary particles at the top of the Earth’s atmosphere. A measurement of at least one of these quantities would be equivalent to a confirmation of the existence of UHE photons, which would give an insight into fundamental physics processes at unprecedentedly high energies, far beyond the reach of man-made accelerators. On the other hand, a lack of such an observation would allow for further constraining of these fundamental processes with the physically new upper limits on UHE photon fluxes after careful analysis of the technical observation ability. The novel advantage of such an approach would lay in the purely electrodynamical character of the underlying simulations which are fully independent on extrapolations of hadronic interaction models by many orders of magnitude. Such extrapolations are necessary in the UHE photon identification methods based on the analyses of properties of individual extensive air showers presently used to determine the UHE photon upper limits. Full article

We derive an analytical approximation for the linear scaling evolution of the characteristic length L and the root-mean-squared velocity ${\sigma }_v$ of standard frictionless domain wall networks in Friedmann–Lemaître–Robertson–Walker universes with a power law evolution of the scale factor a with the cosmic time t ($a\propto t^{\lambda }$). This approximation, obtained using a recently proposed parameter-free velocity-dependent one-scale model for domain walls, reproduces well the model predictions for $\lambda$ close to unity, becoming exact in the $\lambda \to 1^{-}$ limit. We use this approximation, in combination with the exact results found for $\lambda =0$, to obtain a fit to the model predictions valid for $\lambda \in [0,1]$ with a maximum error of the order of $1\%$. This fit is also in good agreement with the results of field theory numerical simulations, especially for $\lambda \in [0.9,1]$. Finally, we explicitly show that the phenomenological energy-loss parameter of the original velocity-dependent one-scale model for domain walls vanishes in the $\lambda \to 1^{-}$ limit and discuss the implications of this result. Full article

The loss of bone mass and alteration in bone physiology during space flight are one of the major health risks for astronauts. Although the lack of weight bearing in microgravity is considered a risk factor for bone loss and possible osteoporosis, organisms living in space are also exposed to cosmic radiation and other environmental stress factors. As such, it is still unclear as to whether and by how much radiation exposure contributes to bone loss during space travel, and whether the effects of microgravity and radiation exposure are additive or synergistic. Bone is continuously renewed through the resorption of old bone by osteoclast cells and the formation of new bone by osteoblast cells. In this study, we investigated the combined effects of microgravity and radiation by evaluating the maturation of a hematopoietic cell line to mature osteoclasts. RAW 264.7 monocyte/macrophage cells were cultured in rotating wall vessels that simulate microgravity on the ground. Cells under static 1g or simulated microgravity were exposed to γ rays of varying doses, and then cultured in receptor activator of nuclear factor-κB ligand (RANKL) for the formation of osteoclast giant multinucleated cells (GMCs) and for gene expression analysis. Results of the study showed that radiation alone at doses as low as 0.1 Gy may stimulate osteoclast cell fusion as assessed by GMCs and the expression of signature genes such as tartrate resistant acid phosphatase (Trap) and dendritic cell-specific transmembrane protein (Dcstamp). However, osteoclast cell fusion decreased for doses greater than 0.5 Gy. In comparison to radiation exposure, simulated microgravity induced higher levels of cell fusion, and the effects of these two environmental factors appeared additive. Interestingly, the microgravity effect on osteoclast stimulatory transmembrane protein (Ocstamp) and Dcstamp expressions was significantly higher than the radiation effect, suggesting that radiation may not increase the synthesis of adhesion molecules as much as microgravity. Full article

In this contribution, we discuss the cosmological scenario where unstable domain walls are formed in the early universe and their late-time annihilation produces a significant amount of gravitational waves. After describing cosmological constraints on long-lived domain walls, we estimate the typical amplitude and frequency of gravitational waves observed today. We also review possible extensions of the standard model of particle physics that predict the formation of unstable domain walls and can be probed by observation of relic gravitational waves. It is shown that recent results of pulser timing arrays and direct detection experiments partially exclude the relevant parameter space, and that a much wider parameter space can be covered by the next generation of gravitational wave observatories. Full article

We discuss the production of massive relic coherent gravitons in a particular class of ƒ(R) gravity, which arises from string theory, and their possible imprint in the Cosmic Microwave Background. In fact, in the very early Universe, these relic gravitons could have acted as slow gravity waves. They may have then acted to focus the geodesics of radiation and matter. Therefore, their imprint on the later evolution of the Universe could appear as filaments and a domain wall in the Universe today. In that case, the effect on the Cosmic Microwave Background should be analogous to the effect of water waves, which, in focusing light, create optical caustics, which are commonly seen on the bottom of swimming pools. We analyze this important issue by showing how relic massive gravity waves (GWs) perturb the trajectories of the Cosmic Microwave Background photons (gravitational lensing by relic GWs). The consequence of the type of physics discussed is outlined by illustrating an amplification of what might be called optical chaos. Full article