Article
Astronomy & Astrophysics
Steven Carlip
Summary: The cosmological constant may be large at the Planck scale but hidden by quantum fluctuations of spacetime. Evidence from a simplified model suggests that a foamy structure can effectively hide a large cosmological constant and persist over time evolution.
Article
Astronomy & Astrophysics
A. Alonso-Serrano, M. Liska
Summary: By heuristically deriving the Hawking temperature and Bekenstein entropy from the existence of a minimal resolvable area, we found quantum gravity corrections that are qualitatively consistent with results obtained by other methods. The size of the minimal area is constrained by semiclassical black hole physics, particularly by the entropy content of Hawking radiation. The derivation method is also applied to finding the Unruh temperature associated with causal diamonds and establishing a new relation between this temperature and the entropy of the causal diamond's horizon.
Review
Physics, Multidisciplinary
S. Carlip
Summary: More than 65 years ago, John Wheeler proposed the concept of 'spacetime foam,' suggesting that quantum uncertainties of the metric would cause significant fluctuations in spacetime geometry and topology at the Planck scale. In this review, various attempts to implement and test this idea, both theoretically and to a lesser extent observationally, are discussed.
REPORTS ON PROGRESS IN PHYSICS
(2023)
Article
Physics, Particles & Fields
Haryanto M. Siahaan
Summary: This study explores the holographic picture for the Kerr-de Sitter spacetime with multiple horizons, demonstrating the existence of hidden conformal symmetry for both black hole and cosmological horizons. Scalar scattering calculations are used in the near region of each horizon to support the holographic approach, showing that the cosmological horizon entropy and associated scalar scattering can be understood through a two-dimensional conformal field theory.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Astronomy & Astrophysics
Antonio Capolupo, Aniello Quaranta
Summary: We analyze the boson mixing in curved spacetime and compute the expectation value of the energy-momentum tensor of bosons on the flavor vacuum in spatially flat Friedmann-Lemaitre-Robertson-Walker metrics. We show that the energy-momentum tensor of the flavor vacuum behaves as the effective energy-momentum tensor of a perfect fluid. The results here presented show that vacuum of mixed bosons like neutrino super-partners, can represent a possible component of the dark energy of the Universe.
Article
Physics, Particles & Fields
Ali Vahedi, Jafar Khodagholizadeh, Arman Tursunov
Summary: This study generalizes previous research on spinning particles around a rotating black hole with a non-zero cosmological constant. The results show that both the particle's spin and the cosmological constant affect the critical value of black hole spin for observing the Aschenbach effect, causing a discrepancy in measurements of spin, cosmological constant, and critical spin in the effect.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Richard S. Wittman, Leon C. Tank
Summary: We investigate whether the solutions to the equations of general relativity predict the existence of observable spacetime, not just its geometry. By considering the simplest case of the general relativity action with a cosmological constant term and a constraint generating the observable measurement condition, we find that the inclusion of the latter implies that a cosmological constant is sufficient for the existence of observable spacetime.
Article
Physics, Mathematical
P. Fernandez De Cordoba, R. Gallego Torrome, S. Gavasso, J. M. Isidro
Summary: This paper investigates an exponentially expanding, flat FLRW Universe filled with a free Schroedinger field and uses the probability fluid of the field to mimic the cosmological fluid. The study computes the matrix representing the cosmological constant and determines the quantum state of the Schroedinger field that best represents the matter contents of the current Universe. Additionally, it provides a measure of the gravitational Boltzmann entropy of the Universe.
INTERNATIONAL JOURNAL OF GEOMETRIC METHODS IN MODERN PHYSICS
(2023)
Article
Astronomy & Astrophysics
F. R. Klinkhamer
Summary: A new approach is proposed to cancel the cosmological constant by utilizing the determinant of the metric as a self-adjusting q-field. The allowed coordinate transformations are restricted to those with unit Jacobian due to the role played by the determinant of the metric in the physics. The study shows the natural cancellation of an initial cosmological constant if quantum-dissipative effects are taken into account.
Article
Astronomy & Astrophysics
J. G. Fernando Barbero, Bogar Diaz, Juan Margalef-Bentabol, Eduardo J. S. Villasenor
Summary: In this paper, we provide a detailed account of the Hamiltonian Gotay-Nester-Hinds (GNH) analysis of the parametrized unimodular extension of the Holst action. The main goal is to derive a simple Hamiltonian formulation for this model using the geometric picture furnished by the GNH method and explain the challenges in arriving at this formulation through other approaches. Additionally, we demonstrate how to utilize the field equations to anticipate the simple form of the constraints found in the paper.
Article
Astronomy & Astrophysics
Luis Rey Diaz-Barron, M. Sabido
Summary: In this work, we investigate the modifications to the Friedmann equations arising from ungravity, with particular focus on the modified entropy-area relation. By using the first law of thermodynamics and the new entropy-area relationship, we derive modified Friedmann equations and discover an effective cosmological constant in the late-time regime. This simple model thus offers an ungravity explanation for the cosmological constant Λ.
Article
Physics, Particles & Fields
Daris Samart, Patinya Ma-adlerd, Peeravit Koad, Phongpichit Channuie
Summary: In this study, we investigated the non-minimally coupled scenario in warm inflation with a quantum-corrected self-interacting potential. By taking into account the interaction between the inflaton and radiation fluid, we found that by choosing proper parameters and a sufficient number of e-folds, our predictions are in good agreement with the latest Planck 2018 results.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
A. Costantini, E. Elizaide
Summary: This study extends the investigation of unimodular Einsteinian gravity in the context of F(R) gravities for constructing anisotropic evolution scenarios. By imposing the unimodular constraint, the metric can be redefined and the desired evolution equations can be obtained. The reconstruction method is demonstrated with characteristic examples.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
Oem Trivedi, Maxim Khlopov
Summary: The study of the true nature of dark energy is an exciting topic in cosmology. In this work, the authors investigate the existence of finite time singularities in scalar field dark energy models based on the RS-II Braneworld. The results show that these models can exhibit various types of singularities under certain initial conditions.
EUROPEAN PHYSICAL JOURNAL C
(2022)
Article
Physics, Particles & Fields
Cristian Moreno-Pulido, Joan Sola Peracaula, Samira Cheraghchi
Summary: Phenomenological work supports the idea of running vacuum energy density with cosmological evolution, helping alleviate cosmological tensions. This study computes fermionic contributions to the energy density and combines them with previous scalar field computations. A new renormalization procedure is used, and the quantum scaling of the energy density is related to cosmic evolution. The equation of state of the vacuum receives quantum corrections, resulting in the appearance of quintessence.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Suchetha Cooray, Tsutomu T. Takeuchi, Takuya Akahori, Yoshimitsu Miyashita, Shinsuke Ideguchi, Keitaro Takahashi, Kiyotomo Ichiki
Summary: Faraday tomography is crucial for studying the magnetic properties of astronomical objects, but current techniques have limitations in accurately reconstructing data. A new algorithm called CRAFT is proposed to address this issue, providing high fidelity reconstructions without relying on specific models, especially excelling in capturing complex features. This approach will be essential for future cosmic magnetism studies, particularly with broad-band polarization data from upcoming telescopes like the Square Kilometre Array.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Kiyoaki Christopher Omori, Tsutomu T. Takeuchi
Summary: By investigating the spatially resolved kinematics and stellar population properties of galaxies with a counter-rotating stellar core, researchers found distinct differences in kinematic and stellar population properties. These differences depend on the classification of the galaxies using spatially resolved emission line diagnostics.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Mutsumi Minoguchi, Atsushi J. Nishizawa, Tsutomu T. Takeuchi, Naoshi Sugiyama
Summary: The distribution of void ellipticity today can be explained well by the tidal field. Through N-body simulations, it is found that some voids show a positive correlation between their ellipticity variation and the tidal field, while others are significantly deformed by particle exchange rather than the tidal field, affecting our ability to accurately probe the quadrupole field of gravity outside the void shape.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2021)
Article
Astronomy & Astrophysics
Yoshiyuki Yajima, Kazuo Sorai, Yusuke Miyamoto, Kazuyuki Muraoka, Nario Kuno, Hiroyuki Kaneko, Tsutomu T. Takeuchi, Atsushi Yasuda, Takahiro Tanaka, Kana Morokuma-Matsui, Masato I. N. Kobayashi
Summary: The study found variations in the line ratio R-2/1 in 24 nearby galaxies, with radial distribution showing differences. When R-2/1 is assumed to be 0.7, the total molecular gas mass derived from (CO)-C-12(J = 2-1) can be underestimated/ overestimated by about 20%-35%. The scatter of molecular gas surface density within each galaxy also increases significantly.
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
(2021)
Article
Astronomy & Astrophysics
Abdurro'uf, Yen-Ting Lin, Hiroyuki Hirashita, Takahiro Morishita, Sandro Tacchella, Masayuki Akiyama, Tsutomu T. Takeuchi, Po-Feng Wu
Summary: This study investigates the spatially resolved properties of stars, dust, and gas in 10 nearby spiral galaxies. By fitting the spatially resolved spectral energy distribution and analyzing the data, the authors draw conclusions about the characteristics of these components.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Kiyoaki Christopher Omori, Tsutomu T. Takeuchi
Summary: By studying galaxy pairs, we find that there is a correlation between mass and metallicity at the local level. However, there are two peaks in the spaxel distribution, which may be related to the projected separation or the stage of interaction of the galaxy pair.
ASTRONOMY & ASTROPHYSICS
(2022)
Article
Astronomy & Astrophysics
Kazuki Y. Nishida, Tsutomu T. Takeuchi, Takuma Nagata, Ryosuke S. Asano
Summary: The spectral energy distribution (SED) of galaxies is significantly affected by dust in its interstellar medium, and the evolution of dust mass and size distribution should be considered in SED modeling. However, many previous SED models have not taken into account the evolution of total mass and size distribution in a physically consistent manner. In this study, a new radiative transfer SED model is constructed to treat the evolution of dust mass and size distribution in a consistent way, and can be used for SED fitting to galaxies at any stage of evolution.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
James O. Chibueze, Hiroki Akamatsu, Viral Parekh, Haruka Sakemi, Takumi Ohmura, Ruby van Rooyen, Takuya Akahori, Hiroyuki Nakanishi, Mami Machida, Tsutomu T. Takeuchi, Oleg Smirnov, Dane Kleiner, Filippo M. Maccagni
Summary: We present the initial results of our MeerKAT L-band observations of Abell 3376. Our observations achieved higher angular resolution and sensitivity compared to previous observations. We successfully calibrated the data and detected relics and radio galaxies.
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
(2023)
Article
Astronomy & Astrophysics
Suchetha Cooray, Tsutomu T. Takeuchi, Shinsuke Ideguchi, Takuya Akahori, Yoshimitsu Miyashita, Keitaro Takahashi
Summary: Wavelet transforms and sparsity analysis are used to improve the accuracy of Faraday tomography through broad-band polarimetry, uncovering previously unseen Faraday complexities. This method is crucial for cosmic magnetism studies using the Square Kilometre Array.
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
(2023)
Article
Astronomy & Astrophysics
Abdurro'uf, Yen-Ting Lin, Hiroyuki Hirashita, Takahiro Morishita, Sandro Tacchella, Po-Feng Wu, Masayuki Akiyama, Tsutomu T. Takeuchi
Summary: We study the spatially resolved scaling relations among stars, dust, and gas in ten nearby spiral galaxies. We find that most of the scaling relations exhibit galaxy-to-galaxy variations in normalization and shape. We further investigate the correlations among the scaling relations and observe indications of the contributions of both global and local factors in governing the star formation process in galaxies.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Atsushi Yasuda, Nario Kuno, Kazuo Sorai, Kazuyuki Muraoka, Yusuke Miyamoto, Hiroyuki Kaneko, Yoshiyuki Yajima, Takahiro Tanaka, Kana Morokuma-Matsui, Tsutomu T. Takeuchi, Masato I. N. Kobayashi
Summary: We conducted simultaneous measurements of the spatially resolved CO-to-H-2 conversion factor (alpha(CO)) and dust-to-gas ratio (DGR) in nearby galaxies on a kiloparsec scale. Our study used (CO)-C-12(J = 1-0) data obtained from the Nobeyama 45 m radio telescope, along with H i and dust mass surface densities. We found that the alpha(CO) values in the outer region of the galaxies were 2.3 to 5.3 times larger than those in the inner region, and that alpha(CO) and DGR correlated with the metallicity and star formation rate surface density.
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
(2023)
Article
Astronomy & Astrophysics
Suchetha Cooray, Tsutomu T. Takeuchi, Daichi Kashino, Shuntaro A. Yoshida, Hai-Xia Ma, Kai T. Kono
Summary: We discovered a 2D Galaxy Manifold in the multidimensional luminosity space of local galaxies. This manifold accurately captures the diversity of galaxies and can estimate galaxy properties with minimal scatter. The manifold's evolution is closely related to gas content, suggesting its close relationship to gas accretion.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Patrick Huber, Hisakazu Minakata, Djordje Minic, Rebekah Pestes, Tatsu Takeuchi
Summary: Neutrino oscillations at JUNO provide a unique opportunity to study Sorkin's triple path interference. The research finds that the bounds on triple path interference by neutrinos are comparable to those from electromagnetic probes, but the neutrino probe is more direct and independent of any boundary conditions compared to electromagnetic probes.
Article
Astronomy & Astrophysics
Djordje Minic, Tatsu Takeuchi, Chia Hsiung Tze
Summary: Nambu quantum mechanics, proposed in 2002, is a deformation of canonical quantum mechanics that modifies only the time-evolution of energy eigenstates phases. The theory's effect on oscillation phenomena is discussed, and a bound on the deformation parameters is placed using data on the atmospheric neutrino mixing angle theta(23).
