Article
Astronomy & Astrophysics
Rajeev Kumar Jain, P. Jishnu Sai, Martin S. Sloth
Summary: This study calculates the primordial correlation between gravitons and a non-minimally coupled abelian gauge field in the early universe, and finds that this correlation satisfies new consistency relations in the three-point cross-correlation functions. The study shows that the interaction between gravitons and gauge fields may have implications for cosmological observables today.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Matthew W. Davies, Pedro Carrilho, David J. Mulryne
Summary: In this study, we work within an idealized framework to match a series of evolution phases defined by the second slow-roll parameter eta. We calculate the reduced bispectrum, f(NL), for inflation models with a significant peak in their primordial power spectra. Our findings show that f(NL) remains relatively constant over the scales where the peak is located, and we provide an analytic approximation for this value. Additionally, we identify the conditions under which f(NL) is large enough to have a significant impact on the production of primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). The analytic formulas for the gradient of the rise and fall in the power spectrum, along with these findings, offer a toolkit for designing or quickly analyzing inflationary models that generate PBHs and SIGWs.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Aliki Litsa, Katherine Freese, Evangelos I. Sfakianakis, Patrick Stengela, Luca Visinellij
Summary: We propose a new way of studying the Higgs potential at extremely high energies by considering the space dependence and non-Gaussianity of the resulting temperature anisotropy spectrum. The observed temperature anisotropies in the Cosmic Microwave Background (CMB) are largely excluded to be primarily caused by Higgs effects. Observational searches for non-Gaussianity in the CMB can be used to constrain the dynamics of the Higgs boson at very high energies.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Sugumi Kanno, Ann Mukuno, Jiro Soda, Kazushige Ueda
Summary: Dark gauge fields have been proposed as potential candidates for dark matter, and if they exist, primordial dark magnetic fields would have existed during inflation. It is believed that primordial gravitational waves arise from quantum fluctuations during inflation. This study investigates the conversion of gravitons into dark photons in the presence of background primordial dark magnetic fields and finds that this process induces a tachyonic instability in the primordial gravitational waves, leading to a peak in their power spectrum. The height of the peak depends on the observation direction, and the peak frequency can range from 10-5 to 103 Hertz for GUT scale inflation, suggesting that the observation of primordial gravitational waves could be a new way to probe primordial dark magnetic fields.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Dionysios Karagiannis, Jose Fonseca, Roy Maartens, Stefano Camera
Summary: The 21 cm emission line of neutral hydrogen can trace dark matter after reionisation; Next-generation intensity mapping surveys may serve as probes of primordial non-Gaussianity; Single-dish surveys typically outperform interferometer surveys in power spectrum but are not competitive in bispectrum.
PHYSICS OF THE DARK UNIVERSE
(2021)
Article
Astronomy & Astrophysics
Mehrdad Mirbabayi, Andrei Gruzinov
Summary: Sphaleron heating is proposed as a mechanism for warm inflation when the inflaton is coupled to pure Yang-Mills as an axion. The presence of heating introduces a friction coefficient gamma proportional to T-3 in the inflaton's equation of motion, as well as a thermal contribution to cosmological fluctuations. In the absence of knowledge about the inflaton potential, non-Gaussianity is the most promising approach for detecting the signatures of this model. By extending previous work, we compute the scalar three-point correlation function and identify distinct features in the squeezed and folded limits. As a detection strategy, we find that combining the equilateral template with a new template yields a high overlap with the shape of non-Gaussianity for 0.01 <= gamma/H <= 1000, with 0.7 < |f(NL)| < 50 in this range.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Sugumi Kanno, Ann Nakato, Jiro Soda, Kazushige Ueda
Summary: There is observational evidence for the existence of primordial magnetic fields generated during inflation. We investigate primordial gravitational waves during inflation in the presence of magnetic fields sustained by a gauge kinetic coupling. In this model, both gravitons as excitations of primordial gravitational waves, and photons as excitations of electromagnetic fields are strongly squeezed, and become entangled through graviton to photon conversion. We calculate the entanglement entropy of the gravitons and find that their state is a mixed state rather than a squeezed state.
Article
Astronomy & Astrophysics
Xingang Chen, Reza Ebadi, Soubhik Kumar
Summary: This study examines features in the inflationary landscape that can inject extra energies into inflation models and produce on-shell particles with masses larger than the Hubble scale, extending the energy reach of cosmological collider physics program. The mechanisms of classical cosmological collider are studied in two categories of primordial features, including classical oscillations and sharp features in the inflation model, which can excite unsuppressed quantum modes of heavy fields leaving observational signatures in primordial non-Gaussianities.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Hemza Azri, Isaac Bamwidhi, Salah Nasri
Summary: This paper explores two-field inflation in the context of purely affine gravity, introducing a covariant formulation that leads to a curved field space allowing for significant departure from purely metric gravity. By allowing specific noncanonical field kinetic terms, the curved field manifold can be flattened, simplifying inflationary dynamics and enabling new predictions.
Article
Astronomy & Astrophysics
Massimo Giovannini
Summary: This article investigates the large-scale magnetic fields generated by the quantum mechanical fluctuations of hypercharge, combined with the evolution of gauge coupling during a long inflationary stage. The results show that the magnetic power spectra can be amplified when the post-inflationary expansion rate is slower than radiation. Furthermore, the study emphasizes that the modulations of the gauge power spectra freeze when the relevant wavelengths reenter the Hubble radius, and the late-time values of the magnetic power spectra can be accurately computed based on these observations.
Article
Astronomy & Astrophysics
Maria Mylova, Marianthi Moschou, Niayesh Afshordi, Joao Magueijo
Summary: This paper introduces a thermal bimetric model and explores its non-Gaussian features, providing precise predictions based on the characteristics of the model. These results are of great significance for future cosmological surveys.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
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
Astronomy & Astrophysics
Fengge Zhang, Yungui Gong, Jiong Lin, Yizhou Lu, Zhu Yi
Summary: The study of non-Gaussianities of primordial curvature perturbations in G-inflation models reveals that even though f(NL) becomes large at certain scales, it remains to be small at peak scales. This suggests that the contributions of non-Gaussianity to scalar induced secondary gravitational waves and primordial black hole abundance are expected to be negligible.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Raphal van Laak, Sam Young
Summary: Primordial black holes are black holes that may have formed in high density regions in the early universe. The fluctuations in their formation rate can be used to constrain the amplitude of non-Gaussianity, especially if primordial black holes make up a significant fraction of dark matter. By extending the calculation to include peaks theory and considering the non-linearities between compaction C and curvature perturbation C, we find that the constraints on quadratic models of non-Gaussianity are largely unchanged, while the constraints on cubic models significantly worsen. If all of the dark matter is composed of primordial black holes, the parameters of non-Gaussianity are -2.9 & BULL; 10-4 < f < 3.8 & BULL; 10-4 and -1.5 & BULL; 10-3 < g < 1.9 & BULL; 10-3 for quadratic and cubic models respectively.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2023)
Article
Astronomy & Astrophysics
Alba Kalaja, P. Daniel Meerburg, Guilherme L. Pimentel, William R. Coulton
Summary: The study investigates the cosmic variance limit on constraining primordial non-Gaussianity for various theory-motivated shapes. It identifies that the scale-invariant N-point correlator's signal-to-noise does not scale as naively expected with the square root of observed modes due to factors such as blurring of the last scattering surface and behavior in squeezed and collapsed limits. Analytical estimates and numerical calculations confirm these findings, and the addition of polarization data enhances scaling for certain spectra.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Tomohiro Fujita, Ippei Obata, Takahiro Tanaka, Kei Yamada
Summary: This paper investigates the effects of dynamical Chern-Simons gravity with the coupling of a scalar field through the Pontryagin density with axion dark matter on gravitational waves, discussing resonant amplification and confirming its occurrence under certain conditions. Amplification of gravitational waves is shown to occur significantly when considering a coherently oscillating axion cloud, with variations in behavior when taking into account random spatial phase distributions of axion oscillations. The possibility of observing resonant amplification of gravitational waves in the present Universe is explored, highlighting potential scenarios where detection may be feasible.
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Astronomy & Astrophysics
So Okano, Tomohiro Fujita
Summary: This study investigates the gravitational wave production induced by primordial magnetic fields in a parity-violating magnetogenesis model and examines their relationship. The research suggests that detectable gravitational waves by LISA, DECIGO, or BBO and strong enough magnetic fields to explain blazar observations can be simultaneously produced and have the same chirality. The amplitudes of the magnetic fields and gravitational waves are related, which can be tested by future observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Tomohiro Fujita, Kai Murai, Ippei Obata, Maresuke Shiraishi
Summary: We study the trispectrum of gravitational waves generated during inflation through the dynamics of an axionic spectator field and SU(2) gauge fields. Non-Abelian gauge theory induces four-point self-interactions in gauge fields, resulting in a tree-level trispectrum of gravitational waves. We formulate and evaluate this type of trispectrum, including non-dynamical contributions, in the equilateral limit as a unique signal of this model. We find that the ratio of the trispectrum to the cube of the scalar power spectrum can be as large as O(10(6)) in the viable parameter space, which could be observed in CMB observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
So Okano, Tomohiro Fujita
Summary: This study numerically investigates the occurrence of Schwinger preheating in different inflation models and finds that it only occurs when there is a sufficiently large coupling between the inflaton and photons in the Starobinsky inflation model.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Tomohiro Fujita, Kaname Imagawa, Kai Murai
Summary: This study proposes a modified chromo-natural inflation model, which considers the enhanced gravitational wave effect and identifies a parameter space that avoids violating the constraints of cosmic microwave background (CMB) observations.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Tomohiro Fujita, Hiromasa Nakatsuka, Ippei Obata, Sam Young
Summary: In this paper, a cosmological scenario is proposed where the particle production of two-form field is triggered by the background motion of the coupled inflaton field and generates observable amounts of primordial black holes as dark matter after inflation. The resultant power spectra of secondary gravitational waves sourced by the curvature perturbation are also computed and shown to be testable with future space-based laser interferometers.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Tomohiro Fujita, Jun'ya Kume, Kyohei Mukaida, Yuichiro Tada
Summary: This study focuses on the axionic inflaton model with the Chern-Simons coupling and finds that the backreaction from charged particles suppresses the amplitude of gauge fields, leading to the dominance of charged particles in the evolution. The findings provide a basis for connecting inflationary models to phenomena such as baryogenesis and magnetogenesis.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Tomohiro Fujita, Kyohei Mukaida, Yuichiro Tada
Summary: In this study, we develop a stochastic formalism for U(1) gauge fields coupled with a rolling pseudo-scalar field during inflation. We derive the Langevin equations for the physical electromagnetic fields and study their analytic solutions. Through numerical simulation, we demonstrate that the averaged electromagnetic fields over the Hubble scale continuously change their direction and fluctuate around the analytically obtained expectation values. While the isotropy is spontaneously broken in each local Hubble patch, it is globally preserved by averaging all the Hubble patches.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2022)
Article
Astronomy & Astrophysics
Yusuke Manita, Katsuki Aoki, Tomohiro Fujita, Shinji Mukohyama
Summary: Bigravity is a natural extension of general relativity that includes an additional massive spin-2 field, which could be a potential candidate for dark matter. In this study, we investigate fixed-point solutions for axisymmetric Bianchi type-I universes in two bigravity theories, namely Hassan-Rosen bigravity and the minimal theory of bigravity, without the presence of a Boulware-Deser ghost. We analyze the local and global stabilities of these fixed points and propose a new scenario where spin-2 dark matter is produced through a transition from an anisotropic fixed-point solution to an isotropic one. The produced spin-2 dark matter can potentially explain all or a fraction of dark matter and can be detected directly using laser interferometers, similar to the detection of gravitational waves.
Article
Astronomy & Astrophysics
Tomoaki Murata, Tomohiro Fujita, Tsutomu Kobayashi
Summary: We investigate the dynamics of pseudoscalar inflation coupled to an SU(N) gauge field, focusing on the isotropization of initially anisotropic universe in this inflation model. By deriving the equations for axisymmetric SU(N) gauge field configurations in Bianchi type-I geometry and identifying the isotropic subsets as late-time attractors, we find that the isotropic universe is a universal attractor in the case of SU(3) gauge field. Furthermore, we discover a possible transition between distinct gauge-field configurations characterized by different SU(2) subalgebras during inflation and clarify the conditions for this transition to occur, which could leave observable imprints on the cosmic microwave background and the primordial gravitational wave background.
Article
Astronomy & Astrophysics
Tomohiro Fujita, Yuto Minami, Maresuke Shiraishi, Shuichiro Yokoyama
Summary: Recently, the cross-correlation between E- and B-mode polarization of the cosmic microwave background has been found, and it can be explained by cosmic birefringence with a rotation angle of approximately 0.3 degrees. However, further investigation shows that this explanation fails to account for the observed EB correlation due to the excessive production of BB autocorrelation.
Article
Astronomy & Astrophysics
Matteo Fasiello, Tomohiro Fujita, Zvonimir Vlah
Summary: In this paper, we provide exact analytic solutions for density and velocity fields in ACDM cosmology using Eulerian standard perturbation theory. The solutions are derived to all orders and have a separable form in time and momenta at each perturbative order.
Article
Astronomy & Astrophysics
Tomohiro Fujita, Kyohei Mukaida, Kai Murai, Hiromasa Nakatsuka
Summary: We study the SU(N) gauge fields coupled with the inflaton through the Chern-Simons coupling and propose a general procedure for constructing solutions of the gauge fields. Specifically, we construct stable solutions for N = 3 and 4 and numerically confirm their completeness and attractor properties. This approach is also applicable to other simple Lie groups.
Article
Astronomy & Astrophysics
Tomohiro Fujita, Kai Murai, Ryo Namba
Summary: We prove the universality of predictions for linear perturbations from the entire class of models of inflation driven by a pseudoscalar field coupled to an SU(N) gauge boson. The effect of which SU(2) subgroup in SU(N) acquires a vacuum expectation value through spontaneous symmetry breaking can be quantified by a single parameter ??. The same dynamics and predictions as in the chromo-natural inflation hold for its SU(N) extension by replacing the gauge coupling constant g with g??. The latter class of models draws the same prediction curve on the ns-r plane as the former at the tree level as long as g?? stays constant during inflation. We briefly discuss possible transitions from one value of ?? to another during inflation and the observational prospects.
Article
Astronomy & Astrophysics
Koji Nagano, Hiromasa Nakatsuka, Soichiro Morisaki, Tomohiro Fujita, Yuta Michimura, Ippei Obata
Summary: The study revisited a scheme for searching for axion dark matter using transmission ports in optical linear cavities, showing that the effect of axion dark matter on the phase of photons traveling an odd number of times in the cavity is not cancelled out. It also improved sensitivity in the low-mass range by taking into account the stochastic nature of the axion field and the availability of two detection ports in the gravitational wave detectors. The sensitivity to the axion-photon coupling was estimated to reach around 3 x 10(-12) GeV-1 for ground-based gravitational wave detectors like Advanced LIGO with 1-year observation, below an axion mass of 10(-15) eV, surpassing the limit achieved by the CERN Axion Solar Telescope.
