Article
Astronomy & Astrophysics
Debottam Nandi
Summary: The simplest form of primordial magnetogenesis can produce scale-invariant magnetic fields, but suffers from strong coupling and backreaction problems. By considering a linear combination of coupling functions and introducing a model parameter, constraints are placed on the parameter to address these issues. This analysis reveals enhanced non-Gaussianity in equilateral and flattened limits, with unique signatures characterizing this model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Yu Li, Le-Yao Zhang
Summary: In this paper, we discussed the dynamics of multiple vector fields during inflation and the generation of magnetic fields during inflation with multiple vector fields. Instead of using a single coupling function in single vector field models, we introduced a coupling matrix between the vector fields and the scalar field responsible for inflation. We derived the dynamical equations for multiple vector fields and applied them to the inflationary era. We discussed three cases for a double-field model, where we found that scale-invariant electric and magnetic spectra can be achieved at the end of inflation without encountering strong coupling or backreaction problems.
MODERN PHYSICS LETTERS A
(2023)
Article
Astronomy & Astrophysics
Petar Simidzija, Achim Kempf, Eduardo Martin-Martinez
Summary: This study calculates the gravitational wave power density emitted by quantum thermal sources, focusing on cosmic microwave background and stellar sources. It investigates the impact of treating gravity classically on thermal emission prediction, finding that the predicted gravitational wave radiation does not exhibit ultraviolet divergence when the fields describing the thermal source are quantum mechanical.
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: The effective approach is applied to the analysis of inflationary magnetogenesis, considering generally covariant terms with four space-time derivatives and weightings by inflaton-dependent couplings. The higher derivatives are suppressed by negative powers of a typical mass scale. This leads to an asymmetry between hypermagnetic and hyperelectric susceptibilities during a quasi-de Sitter stage.
Article
Astronomy & Astrophysics
Teppei Minoda, Kiyotomo Ichiki, Hiroyuki Tashiro
Summary: This paper investigates how primordial magnetic fields (PMFs) in the early universe affect cosmic microwave background (CMB) anisotropies, and constrains the PMFs using data from Planck and South Pole Telescope (SPT). The results indicate that the SPT data support a PMF model with small scale dependence.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
R. Durrer, O. Sobol, S. Vilchinskii
Summary: In this study, we investigate the generation of Abelian gauge fields in the framework of mixed Higgs-Starobinsky inflation. By coupling the gauge fields to gravity with nonminimal couplings, we derive the power spectra, energy densities, correlation length, and helicality of the generated gauge fields. Our results show that it is possible to obtain scale-invariant or red-tilted spectra for the gauge fields under certain conditions.
Article
Astronomy & Astrophysics
Sayan Mandal, Neelima Sehgal, Toshiya Namikawa
Summary: The origin of mu G magnetic fields in galaxies is unknown. It is possible that magnetic fields generated during inflation were compressed to mu G strengths in galaxies during structure formation. Future CMB surveys may be able to detect these inflationary primordial magnetic fields, providing evidence for inflation.
Article
Astronomy & Astrophysics
Axel Brandenburg, Yutong He, Ramkishor Sharma
Summary: In this study, numerical simulations of helical inflationary magnetogenesis in a low reheating temperature scenario show that the magnetic energy spectrum peaks strongly at a specific wavenumber. Gravitational waves are generated in the frequency range of 3 nHz to 50 mHz, depending on the reheating temperature, with a stress spectrum resembling white noise below the peak frequency. The presence of helicity extends the peak of the gravitational wave spectrum, leading to potential detectability with space interferometers at larger frequencies.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: The study analyzes large-scale magnetogenesis within the Palatini approach, finding that the addition of nonlinear terms can suppress the tensor-to-scalar ratio. A stiff phase may follow the standard inflationary stage if the potential has a quintessential form.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Misao Sasaki, Valeri Vardanyan, Vicharit Yingcharoenrat
Summary: We propose a novel mechanism to enhance the amplitude of primordial electromagnetic fields during inflation. Our scenario differs significantly from previously studied models and avoids their shortcomings. We argue that a mass term for the gauge sector is required for the resonant scenario to work with a bounded and positive-definite coupling function.
Article
Physics, Particles & Fields
Massimo Giovannini
Summary: The production of hypermagnetic gyrotropy is investigated under the assumption of smooth evolution of gauge coupling in a quasi-de Sitter phase, with the weight of pseudoscalar interactions being modest to avoid major deviations from homogeneity during inflationary phase. An approximate duality symmetry constrains the late-time form of hypermagnetic power spectra, with magnetic power spectra associated with modes reentering after symmetry breaking possibly reaching a few hundredths of a nG over typical length scales comparable to Mpc.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Axel Brandenburg, Ramkishor Sharma
Summary: A study using three-dimensional simulations investigates the production of magnetic fields and gravitational waves in the early universe, finding that turbulence may not be as effective in driving gravitational waves as previously thought. Magnetic energy densities are found to be between 0.03% and 0.5% of the critical energy density at the end of reheating, with gravitational wave spectra extending to higher frequencies in specific models with reheating temperatures around 100 GeV during the early radiation-dominated era.
ASTROPHYSICAL JOURNAL
(2021)
Article
Astronomy & Astrophysics
Emanuela Dimastrogiovanni, Matteo Fasiello, A. Emir Gumrukcuoglu
Summary: This paper investigates the possibility of extra spinning particles during inflation, focusing on the spin-2 case. The study explores the parameter space of the inflationary Lagrangian and identifies regions with signatures detectable by upcoming CMB probes. The analysis reveals the presence of a local-type non-Gaussianity in the gravitational wave spectrum and three-point function, which may be within the sensitivity range of both LiteBIRD and CMB-S4 experiments.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Optics
Sohail A. Jalil, Kashif M. Awan, Joshua Baxter, Graeme Bart, David N. Purschke, Thomas Fennel, David M. Villeneuve, Andre Staudte, Pierre Berini, Thomas Brabec, Lora Ramunno, Giulio Vampa
Summary: The study demonstrates that the field gradient of a nanoscale plasmonic hotspot inside a Si crystal induces the emission of even-order high harmonics from the crystal itself, expanding the complementary electron-photon perspective on attosecond science to nanoscale systems.
LASER & PHOTONICS REVIEWS
(2023)
Article
Astronomy & Astrophysics
F. Pucci, M. Viviani, F. Valentini, G. Lapenta, W. H. Matthaeus, S. Servidio
Summary: We demonstrate an efficient mechanism for generating magnetic fields in turbulent, collisionless plasmas through fully kinetic, particle-in-cell simulations. The complex motion is initiated via a Taylor-Green vortex, and the plasma locally develops strong electron temperature anisotropy, due to the strain tensor of the turbulent flow. Subsequently, in a domino effect, the anisotropy triggers a Weibel instability which leads to magnetization.
ASTROPHYSICAL JOURNAL LETTERS
(2021)
Article
Astronomy & Astrophysics
Massimo Giovannini
Article
Astronomy & Astrophysics
Massimo Giovannini
CLASSICAL AND QUANTUM GRAVITY
(2019)
Review
Physics, Nuclear
Massimo Giovannini
PROGRESS IN PARTICLE AND NUCLEAR PHYSICS
(2020)
Article
Physics, Nuclear
Massimo Giovannini
INTERNATIONAL JOURNAL OF MODERN PHYSICS A
(2020)
Article
Astronomy & Astrophysics
Massimo Giovannini
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2020)
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: This study examines the impact of time-varying gauge coupling on the hyper electromagnetic spectrum, investigates the process of magnetic field generation through continuous evolution of mode functions, categorizes amplified gauge power spectra according to duality symmetry, and explores the conditions for magnetic field generation through scrutiny of parameter space.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: The effective approach is applied to the analysis of inflationary magnetogenesis, considering generally covariant terms with four space-time derivatives and weightings by inflaton-dependent couplings. The higher derivatives are suppressed by negative powers of a typical mass scale. This leads to an asymmetry between hypermagnetic and hyperelectric susceptibilities during a quasi-de Sitter stage.
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: This study investigates the absorption of high-frequency gravitons by matter during the cosmic evolution, with the sound speed and viscosity of the medium affecting the spectral energy density of the gravitons.
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: If gauge fields are amplified from the inflationary vacuum, quantum mechanical initial data will evolve into standing waves whose phases depend on the evolution of the gauge coupling. These gauge analogs of Sakharov oscillations are constrained by duality symmetry, affecting the scaling and final asymptotic values of the hypermagnetic power spectra. The late-time value of the magnetic field is determined by the moment when the wavelengths become comparable to the Hubble radius.
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: The early expansion history of the Universe is studied by combining limits on cosmic gravitons and evidences in the nHz domain. Multiple postinflationary stages can lead to a spectral energy density that undershoots signals from relic gravitons, but eventually reaches a maximum value. The presence of a secondary stage of inflation at low scales can modify the effective expansion rate and result in a spectral energy density that is blue above a certain frequency and then flattens out.
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: The slopes of superhorizon hypermagnetic spectra generated by changes in gauge couplings are not significantly influenced by parity-breaking terms. A new method is proposed for estimating gauge power spectra during inflation with pseudoscalar interactions. The impact of pseudoscalar contributions on magnetogenesis requirements is minimal.
Article
Astronomy & Astrophysics
Massimo Giovannini
Article
Astronomy & Astrophysics
Massimo Giovannini
Article
Astronomy & Astrophysics
Massimo Giovannini
Article
Astronomy & Astrophysics
Massimo Giovannini
Article
Astronomy & Astrophysics
Nelson R. F. Braga, Octavio C. Junqueira
Summary: This study investigates the influence of rotation on the transition temperature of strongly interacting matter produced in non-central heavy ion collisions. By using a holographic description of an AdS black hole, the authors extend the analysis to the more realistic case where the matter spreads over a region around the rotational axis. The results show the coexistence of confined and deconfined phases and are consistent with the concept of local temperature in rotating frames developed by Tolman and Ehrenfest.
Article
Astronomy & Astrophysics
Bing Sun, Jiachen An, Zhoujian Cao
Summary: This paper investigates the effect of gravitational constant variation on the propagation of gravitational waves. By employing two analytical methods, the study finds that variations in the gravitational constant result in amplitude and phase corrections for gravitational waves, and the time variation of the gravitational constant can be constrained through the propagation of gravitational waves.
Article
Astronomy & Astrophysics
Abdellah Touati, Zaim Slimane
Summary: This letter presents the first study of Hawking radiation as a tunneling process within the framework of non-commutative gauge theory of gravity. The non-commutative Schwarzschild black hole is reconstructed using the Seiberg-Witten map and the star product. The emission spectrum of outgoing massless particles is computed using the quantum tunneling mechanism. The results reveal pure thermal radiation in the low-frequency scenario, but a deviation from pure thermal radiation in the high-frequency scenario due to energy conservation. It is also found that noncommutativity enhances the correlations between successively emitted particles.
Article
Astronomy & Astrophysics
Shahar Hod
Summary: The travel times of light signals between two antipodal points on a compact star's surface are calculated for two different trajectories. It is shown that, for highly dense stars, the longer trajectory along the surface may have a shorter travel time as measured by asymptotic observers. A critical value of the dimensionless density-area parameter is determined for constant density stars to distinguish cases where crossing through the star's center or following a semi-circular trajectory on the surface has a shorter travel time as measured by asymptotic observers.
