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
Haximjan Abdusattar
Summary: In this work, we examine the stability and phase structure of AdS black holes with either a Maxwell field or a phantom field. We analyze the free energy and temperature of these systems in both the canonical and grand canonical ensembles. Our results reveal a phase transition in the grand canonical ensemble, similar to the Hawking-Page-like phase transition observed in AdS spacetime between thermal radiation and thermodynamically stable large black holes. We present graphical representations of these phase transitions on free energy-temperature diagrams for the black holes. Finally, we obtain the transition temperature, minimum temperature, and their dual relationships.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Physics, Particles & Fields
Haximjan Abdusattar
Summary: In this study, we investigate the thermodynamic stability and phase structure of AdS black holes and identify a phase transition in the grand canonical ensemble. Graphical representations of the phase transitions are presented on free energy-temperature diagrams for the black holes.
EUROPEAN PHYSICAL JOURNAL C
(2023)
Article
Astronomy & Astrophysics
Ming-Da Li, Hui-Min Wang, Shao-Wen Wei
Summary: Quasitopological electromagnetism has an important influence on the strong gravity of dyonic black holes, leading to the discovery of three photon spheres and a special phase structure. These results reveal the intriguing thermodynamic properties of dyonic AdS black holes with quasitopological electromagnetism.
Article
Physics, Particles & Fields
Sergiu I. Vacaru, Elsen Veli Veliev, Laurentiu Bubuianu
Summary: We develop an approach to relativistic geometric flows and emergent gravity using entropy functionals and statistical thermodynamics models. Our analysis shows possible connections between nonholonomic Ricci flows and modified gravity theories, and we construct new classes of exact and parametric solutions for nonstationary configurations.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
F. R. Klinkhamer
Summary: We study a cosmological model where the metric determinant has a dynamical role, and present numerical results on the cancellation of vacuum energy density with the inclusion of a cosmological constant. The model's action is only invariant under restricted coordinate transformations with a unit Jacobian, similar to the approach of unimodular gravity. We propose that the nonstandard terms in the matter action of the model can potentially arise from emergent gravity in the IIB matrix model, a nonperturbative formulation of superstring theory.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Astronomy & Astrophysics
Lautaro Amadei, Alejandro Perez
Summary: This paper proposes a new inflation model driven by the relaxation of an initially Planckian cosmological constant. The model can generate a (approximately) scale invariant spectrum of (adiabatic) primordial perturbations with the correct amplitudes and red tilt without the need of an inflaton. The inhomogeneities observed in the cosmic microwave background (CMB) are caused by the fundamental Planckian granularity imprinted in the standard model Higgs scalar fluctuations during the inflationary phase. The deviations from scale invariance observed in the CMB are controlled by the self-coupling constant of the Higgs scalar of the standard model of particle physics. The thermal production of primordial black holes can account for the required amount of cold dark matter determined by observations.
Article
Astronomy & Astrophysics
Christoph Schiller
Summary: Two methods are presented to deduce the equivalence of the field equations of general relativity and the principle of maximum force c(4)/4G. A simple deduction of inverse square gravity from maximum force is proposed. The author refutes recent apparent counter arguments and proposes new tests of the principle in various fields.
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
Physics, Multidisciplinary
R. B. Alfaia, I. P. Lobo, L. C. T. Brito
Summary: In this study, we analyzed the extended phase space thermodynamics of Kiselev black hole by introducing a central charge and allowing the gravitational constant to vary. We discussed the relationship between the chemical potential and the black hole size, as well as presented a new description of phase transitions. The conclusion drawn is that the universality of the central charge is not always valid.
EUROPEAN PHYSICAL JOURNAL PLUS
(2022)
Article
Physics, Particles & Fields
Serena Giardino, Andrea Giusti, Valerio Faraoni
Summary: This article analyzes the stealth solutions of scalar-tensor gravity and less-known generalizations of de Sitter spaces, examining their potential role as thermal equilibria at non-zero temperature in the new first-order thermodynamics of scalar-tensor gravity. No stable equilibria are discovered, further confirming the exceptional status of general relativity as an equilibrium state in the landscape of gravity theories, as seen through the lens of first-order thermodynamics.
EUROPEAN PHYSICAL JOURNAL C
(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
Sumanta Chakraborty, T. Padmanabhan
Summary: The study presents an action principle in the framework of Eddington gravity that incorporates matter fields in a simple way, deriving gravitational field equations identical to Einstein's equations and explaining the origin of the cosmological constant. The approach strongly supports the paradigm that gravity is an emergent phenomenon and discusses various extensions.
Article
Astronomy & Astrophysics
Gopal Yadav, Nitin Joshi
Summary: In this study, the researchers analyzed the information paradox and its resolution in Schwarzschild de-Sitter black hole spacetime using the island proposal. They found that the black hole island is located inside the black hole event horizon, contrary to the universal result for eternal black holes, and the cosmological island is also located inside the cosmological event horizon. Moreover, they studied the effect of temperature on Page curves and observed that low-temperature black hole/de-Sitter patch exhibits Page curves at later times, while high-temperature black hole/de-Sitter patch shows the opposite behavior.
Article
Astronomy & Astrophysics
Hamsa Padmanabhan, Abraham Loeb
Summary: The researchers discussed the potential origin of double-peaked profiles observed in Lyman-alpha emitters during the epoch of reionization, suggesting they may come from obscured AGN. By comparing the luminosities of AGN with similar quasar samples at these epochs, they estimated the extent of AGN obscuration. Future X-ray, radio, and James Webb Space Telescope observations will be important for testing the contribution of AGN to intergalactic-scale ionization zones of high-redshift LAEs.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Hamsa Padmanabhan, Abraham Loeb
Summary: The contribution of tidal disruption events (TDEs) to the flares in Active Galactic Nuclei (AGN) at high redshifts was explored. It was found that at low redshifts, a few percent of AGN with bolometric luminosities less than or similar to 10(44) erg s(-1) may be attributable to TDEs, with this fraction significantly increasing at earlier cosmic times, including up to several tens of percent of AGN at z greater than or similar to 3. Further calibrations with upcoming X-ray missions and spectroscopic surveys targeting TDE-AGN are motivated by these findings.
ASTRONOMY & ASTROPHYSICS
(2021)
Article
Astronomy & Astrophysics
Obinna Umeh, Roy Maartens, Hamsa Padmanabhan, Stefano Camera
Summary: This passage discusses post-reionisation 21cm intensity mapping experiments targeting the spectral line of neutral hydrogen in dark matter haloes, and explores the impact of halo physical size on the statistical properties of HI power spectra. It also highlights how finite halo size results in a cancellation of certain noise features and leads to sub-Poissonian noise signatures on large scales.
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2021)
Article
Astronomy & Astrophysics
Hamsa Padmanabhan, Abraham Loeb
Summary: This study illustrates the observability of the end stages of the earliest (Population III) stars at high redshifts z greater than or similar to 10, using the recently observed transient, GN-z11-flash as an example. The observed spectrum of this transient suggests that it may originate from a shock-breakout in a Population III supernova in the GN-z11 galaxy at z similar to 11. The study also provides a forecast of the expected number of such transients from z > 10 galaxies in the future.
GENERAL RELATIVITY AND GRAVITATION
(2022)
Article
Astronomy & Astrophysics
Hamsa Padmanabhan, Abraham Loeb
Summary: We present a novel signature of black hole binaries by analyzing the kinematics of water maser emission in their environments. Our results show that binary black holes exhibit distinct kinematic and spectral differences compared to single black holes, with the blueshifted masers following Keplerian rotation curve and the redshifted masers deviating from this relation. The double peaked structure in the spectrum of masers suggests the potential for identifying binary black hole candidates.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
James W. Lamb, Kieran A. Cleary, David P. Woody, Morgan Catha, Dongwoo T. Chung, Joshua Ott Gundersen, Stuart E. Harper, Andrew I. Harris, Richard Hobbs, Havard T. Ihle, Jonathon Kocz, Timothy J. Pearson, Liju Philip, Travis W. Powell, Lilian Basoalto, J. Richard Bond, Jowita Borowska, Patrick C. Breysse, Sarah E. Church, Clive Dickinson, Delaney A. Dunne, Hans Kristian Eriksen, Marie Kristine Foss, Todd Gaier, Junhan Kim, Charles R. Lawrence, Jonas G. S. Lunde, Hamsa Padmanabhan, Maren Rasmussen, Anthony C. S. Readhead, Rodrigo Reeves, Thomas J. Rennie, Nils-Ole Stutzer, Marco P. Viero, Duncan J. Watts, Ingunn Kathrine Wehus
Summary: Line intensity mapping is a new technique for tracing the global properties of galaxies, and the CO Mapping Project Pathfinder is an instrument designed to detect redshifted carbon monoxide with high precision and frequency range.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Kieran A. Cleary, Jowita Borowska, Patrick C. Breysse, Morgan Catha, Dongwoo T. Chung, Sarah E. Church, Clive Dickinson, Hans Kristian Eriksen, Marie Kristine Foss, Joshua Ott Gundersen, Stuart E. Harper, Andrew Harris, Richard Hobbs, Havard T. Ihle, Junhan Kim, Jonathon Kocz, James W. Lamb, Jonas G. S. Lunde, Hamsa Padmanabhan, Timothy J. Pearson, Liju Philip, Travis W. Powell, Maren Rasmussen, Anthony C. S. Readhead, Thomas J. Rennie, Marta B. Silva, Nils-Ole Stutzer, Bade D. Uzgil, Duncan J. Watts, Ingunn Kathrine Wehus, David P. Woody, Lilian Basoalto, J. Richard Bond, Delaney A. Dunne, Todd Gaier, Brandon Hensley, Laura C. Keating, Charles R. Lawrence, Norman Murray, Roberta Paladini, Rodrigo Reeves, Marco P. Viero, Risa H. Wechsler
Summary: The CO Mapping Array Project aims to trace the distribution and properties of galaxies using line intensity mapping of carbon monoxide (CO). Through observations using the Pathfinder instrument, which is sensitive to CO emissions, the researchers have obtained direct constraints on the clustering component of the CO power spectrum. These constraints significantly improve upon previous measurements.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Havard T. Ihle, Jowita Borowska, Kieran A. Cleary, Hans Kristian Eriksen, Marie K. Foss, Stuart E. Harper, Junhan Kim, Jonas G. S. Lunde, Liju Philip, Maren Rasmussen, Nils-Ole Stutzer, Bade D. Uzgil, Duncan J. Watts, Ingunn Kathrine Wehus, J. Richard Bond, Patrick C. Breysse, Morgan Catha, Sarah E. Church, Dongwoo T. Chung, Clive Dickinson, Delaney A. Dunne, Todd Gaier, Joshua Ott Gundersen, Andrew Harris, Richard Hobbs, James W. Lamb, Charles R. Lawrence, Norman Murray, Anthony C. S. Readhead, Hamsa Padmanabhan, Timothy J. Pearson, Thomas J. Rennie, David P. Woody
Summary: This article presents the power spectrum methodology used in the first-season COMAP analysis and evaluates the quality of the current data set. Using the Feed-Feed Pseudo-Cross-Spectrum (FPXS) method, the main results are derived, and both noise modeling errors and experimental systematics are taken into account. By applying effective transfer functions, the effects of instrumental beam smoothing and various filter operations are considered. The power spectra obtained in this way help identify a systematic error related to one of the scanning strategies and demonstrate that uncertainties integrate as expected. The FPXS method allows for the estimation of the clustering component of the CO(1-0) power spectrum.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Patrick C. Breysse, Dongwoo T. Chung, Kieran A. Cleary, Havard T. Ihle, Hamsa Padmanabhan, Marta B. Silva, J. Richard Bond, Jowita Borowska, Morgan Catha, Sarah E. Church, Delaney A. Dunne, Hans Kristian Eriksen, Marie Kristine Foss, Todd Gaier, Joshua Ott Gundersen, Andrew Harris, Richard Hobbs, Laura Keating, James W. Lamb, Charles R. Lawrence, Jonas G. S. Lunde, Norman Murray, Timothy J. Pearson, Liju Philip, Maren Rasmussen, Anthony C. S. Readhead, Thomas J. Rennie, Nils-Ole Stutzer, Marco P. Viero, Duncan J. Watts, Ingunn Kathrine Wehus, David P. Woody
Summary: COMAP-EoR is a project aimed at extending CO intensity mapping to the Epoch of Reionization. By adding instruments and a receiver, COMAP-EoR is able to map CO(1-0) and CO(2-1) at reionization redshifts, providing valuable insights into cosmic history.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Marie K. Foss, Havard T. Ihle, Jowita Borowska, Kieran A. Cleary, Hans Kristian Eriksen, Stuart E. Harper, Junhan Kim, James W. Lamb, Jonas G. S. Lunde, Liju Philip, Maren Rasmussen, Nils-Ole Stutzer, Bade D. Uzgil, Duncan J. Watts, Ingunn K. Wehus, David P. Woody, J. Richard Bond, Patrick C. Breysse, Morgan Catha, Sarah E. Church, Dongwoo T. Chung, Clive Dickinson, Delaney A. Dunne, Todd Gaier, Joshua Ott Gundersen, Andrew Harris, Richard Hobbs, Charles R. Lawrence, Norman Murray, Anthony C. S. Readhead, Hamsa Padmanabhan, Timothy J. Pearson, Thomas J. Rennie
Summary: We describe the analysis pipeline of the first-season CO Mapping Array Project (COMAP) that converts raw detector readouts to calibrated sky maps. This pipeline includes four main steps: gain calibration, filtering, data selection, and mapmaking. The resulting data set and maps are analyzed and evaluated in terms of data processing and observing efficiencies.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Dongwoo T. Chung, Patrick C. Breysse, Kieran A. Cleary, Havard T. Ihle, Hamsa Padmanabhan, Marta B. Silva, J. Richard Bond, Jowita Borowska, Morgan Catha, Sarah E. Church, Delaney A. Dunne, Hans Kristian Eriksen, Marie Kristine Foss, Todd Gaier, Joshua Ott Gundersen, Stuart E. Harper, Andrew Harris, Brandon Hensley, Richard Hobbs, Laura C. Keating, Junhan Kim, James W. Lamb, Charles R. Lawrence, Jonas Gahr Sturtzel Lunde, Norman Murray, Timothy J. Pearson, Liju Philip, Maren Rasmussen, Anthony C. S. Readhead, Thomas J. Rennie, Nils-Ole Stutzer, Bade D. Uzgil, Marco P. Viero, Duncan J. Watts, Risa H. Wechsler, Ingunn Kathrine Wehus, David P. Woody
Summary: This article presents the current state of models for the carbon monoxide (CO) line intensity signal at redshift z similar to 3, which is targeted by the CO Mapping Array Project (COMAP) Pathfinder. The Pathfinder's early science results provide a direct 3D constraint on the clustering component of the CO (1-0) power spectrum and improve upon previous indirect measurements. The study also demonstrates the complementary nature of COMAP and interferometric CO surveys, and provides forecasts for future detection of the CO power spectrum and the CO-galaxy cross-spectrum.
ASTROPHYSICAL JOURNAL
(2022)
Article
Astronomy & Astrophysics
Hamsa Padmanabhan, Patrick Breysse, Adam Lidz, Eric R. Switzer
Summary: This study forecasts the ability of future experiments to detect the fine-structure lines of carbon and oxygen ions during the Epoch of Reionization. The authors also propose methods to improve ground-based and balloon-based surveys, as well as a space-based mission for enhanced cross-correlation measurements.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2022)
Article
Astronomy & Astrophysics
Dongwoo T. Chung, Ishika Bangari, Patrick C. Breysse, Havard T. Ihle, J. Richard Bond, Delaney A. Dunne, Hamsa Padmanabhan, Liju Philip, Thomas J. Rennie, Marco P. Viero
Summary: We propose the deconvolved distribution estimator (DDE) as an extension of the voxel intensity distribution (VID) in future observations for the CO Mapping Array Project (COMAP). The DDE utilizes the convolution property of the observed VID, which is a combination of correlated signal intensity distributions and uncorrelated noise or interloper intensity distributions. By deconvolving the individual VID from their joint VID in Fourier-space, the DDE reduces sensitivity to interloper emission while maintaining sensitivity to correlated components. The DDE improves upon the VID by minimizing the influence of uncorrelated noise and interloper biases, making it valuable for COMAP observations.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Astronomy & Astrophysics
Hamsa Padmanabhan, Abraham Loeb
Summary: We use CHIME catalog data on fast radio bursts (FRBs) to obtain an upper limit on the magnetic field in the intergalactic medium (IGM) on subkiloparsec scales. A nonmagnetized, photoionized IGM cannot explain the scattering of FRBs at all redshifts, but a warm-hot component is marginally consistent with data at z ~ 1. Including a nonzero magnetic field as the lower limit of the smearing distribution leads to upper limits of B < 10-30 nG on scales of 0.07-0.20 kpc in the IGM at z ~ 1-2. Our study introduces a novel technique to constrain small-scale magnetic fields in the IGM, which has not been explored by FRB rotation and dispersion measures.
ASTROPHYSICAL JOURNAL LETTERS
(2023)
Article
Astronomy & Astrophysics
Hamsa Padmanabhan
Summary: We use ALMA surveys targeting the [C ii] and [O iii] lines, combined with predictions for the evolution of H i, to explore the cross-correlations between 21 cm and submillimetre surveys. Our results show that the [C ii] luminosity-halo mass relation can be described by a double power law, and the autopower spectrum of [C ii] can be detected at all redshifts with an enhanced configuration. We also find that a balloon-borne experiment can detect the 21 cm - [O iii] cross-correlation with the MWA and SKA-LOW out to z similar to 7.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
