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51. Gravitational Waves in Viable f(R) Models

Author

Yang, Louis, Lee, Chung-Chi, and Geng, Chao-Qiang

Subjects
Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology
Abstract

We study gravitational waves in viable $f(R)$ theories under a non-zero background curvature. In general, an $f(R)$ theory contains an extra scalar degree of freedom corresponding to a massive scalar mode of gravitational wave. For viable $f(R)$ models, since there always exits a de-Sitter point where the background curvature in vacuum is non-zero, the mass squared of the scalar mode of gravitational wave is about the de-Sitter point curvature $R_{d}\sim10^{-66}eV^{2}$. We illustrate our results in two types of viable $f(R)$ models: the exponential gravity and Starobinsky models. In both cases, the mass will be in the order of $10^{-33}eV$ when it propagates in vacuum. However, in the presence of matter density in galaxy, the scalar mode can be heavy. Explicitly, in the exponential gravity model, the mass becomes almost infinity, implying the disappearance of the scalar mode of gravitational wave, while the Starobinsky model gives the lowest mass around $10^{-24}eV$, corresponding to the lowest frequency of $10^{-9}$ Hz, which may be detected by the current and future gravitational wave probes, such as LISA and ASTROD-GW., Comment: 18 pages, 6 figures, several statements and references added

Published
2011
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52. Equation of state for dark energy in $f(T)$ gravity

Author

Bamba, Kazuharu, Geng, Chao-Qiang, Lee, Chung-Chi, and Luo, Ling-Wei

Subjects
Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology
Abstract

We study the cosmological evolutions of the equation of state for dark energy $w_{\mathrm{DE}}$ in the exponential and logarithmic as well as their combination $f(T)$ theories. We show that the crossing of the phantom divide line of $w_{\mathrm{DE}} = -1$ can be realized in the combined $f(T)$ theory even though it cannot be in the exponential or logarithmic $f(T)$ theory. In particular, the crossing is from $w_{\mathrm{DE}} > -1$ to $w_{\mathrm{DE}} < -1$, in the opposite manner from $f(R)$ gravity models. We also demonstrate that this feature is favored by the recent observational data., Comment: 24 pages, 12 figures, version accepted for publication in JCAP

Published
2010
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53. Observational Constraints on Exponential Gravity

Author

Yang, Louis, Lee, Chung-Chi, Luo, Ling-Wei, and Geng, Chao-Qiang

Subjects
Astrophysics - Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Phenomenology
Abstract

We study the observational constraints on the exponential gravity model of f(R)=-beta*Rs(1-e^(-R/Rs)). We use the latest observational data including Supernova Cosmology Project (SCP) Union2 compilation, Two-Degree Field Galaxy Redshift Survey (2dFGRS), Sloan Digital Sky Survey Data Release 7 (SDSS DR7) and Seven-Year Wilkinson Microwave Anisotropy Probe (WMAP7) in our analysis. From these observations, we obtain a lower bound on the model parameter beta at 1.27 (95% CL) but no appreciable upper bound. The constraint on the present matter density parameter is 0.245< Omega_m^0<0.311 (95% CL). We also find out the best-fit value of model parameters on several cases., Comment: 14pages, 3 figures, accepted by PRD

Published
2010
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54. Comment on 'Einstein's Other Gravity and the Acceleration of the Universe'

Author

Bamba, Kazuharu, Geng, Chao-Qiang, and Lee, Chung-Chi

Subjects
Astrophysics - Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology
Abstract

We show that in the exponential $f(T)$ model studied by E. Linder [arXiv:1005.3039, Phys.Rev.D 81, 127301 (2010)], it is impossible to have the crossing of the phantom divide line $w_{\mathrm{DE}}=-1$., Comment: 2 pages, 1 figure

Published
2010

55. Generic feature of future crossing of phantom divide in viable $f(R)$ gravity models

Author

Bamba, Kazuharu, Geng, Chao-Qiang, and Lee, Chung-Chi

Subjects
Astrophysics - Cosmology and Nongalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Theory
Abstract

We study the equation of state for dark energy and explicitly demonstrate that the future crossings of the phantom divide line $w_{\mathrm{DE}}=-1$ are the generic feature in the existing viable $f(R)$ gravity models. We also explore the future evolution of the cosmological horizon entropy and illustrate that the cosmological horizon entropy oscillates with time due to the oscillatory behavior of the Hubble parameter. The important cosmological consequence is that in the future, the sign of the time derivative of the Hubble parameter changes from negative to positive in these viable $f(R)$ gravity models., Comment: 12 pages, 3 figures, accepted for publication in JCAP

Published
2010
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56. Cosmological evolution in exponential gravity

Author

Bamba, Kazuharu, Geng, Chao-Qiang, and Lee, Chung-Chi

Subjects
Astrophysics - Cosmology and Extragalactic Astrophysics, General Relativity and Quantum Cosmology, High Energy Physics - Theory
Abstract

We explore the cosmological evolution in the exponential gravity $f(R)=R +c_1 (1-e^{- c_2 R})$ ($c_{1, 2} = \mathrm{constant}$). We summarize various viability conditions and explicitly demonstrate that the late-time cosmic acceleration following the matter-dominated stage can be realized. We also study the equation of state for dark energy and confirm that the crossing of the phantom divide from the phantom phase to the non-phantom (quintessence) one can occur. Furthermore, we illustrate that the cosmological horizon entropy globally increases with time., Comment: Published version in JCAP

Published
2010
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58. Convergence properties of fine structure constant measurements using quasar absorption systems.

Author

Webb, John K and Lee, Chung-Chi

Subjects
*FINE-structure constant, *QUASARS, *ABSORPTION, *INDUSTRIALIZED building, *X-ray absorption near edge structure
Abstract

Searches for space–time variations of fundamental constants have entered an era of unprecedented precision. New, high-quality quasar spectra require increasingly refined analytical methods. In this paper, a continuation in a series to establish robust and unbiased methodologies, we explore how convergence criteria in non-linear least-squares optimization impact on quasar absorption system measurements of the fine structure constant α. Given previous claims for high-precision constraints, we critically examine the veracity of a so-called blinding approach, in which α is fixed at the terrestrial value during the model building process, releasing it as a free parameter only after the 'final' absorption system kinematic structure has been obtained. We show that this approach results in such small consecutive parameter steps during minimization that convergence is unlikely to be reached, even after as many as 1000 iterations. The fix is straightforward: α must be treated as a free parameter from the earliest possible stages of absorption system model building. The implication of the results presented here is that all previous measurements that have used initially fixed α should be reworked. [ABSTRACT FROM AUTHOR]

Published
2024
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65. Avoiding Bias in Measurements of Fundamental Constants from High Resolution Quasar Spectra

Author

Lee Chung-Chi, John Webb, and Dinko Milaković

Subjects
Cosmology and Nongalactic Astrophysics (astro-ph.CO), General Physics and Astronomy, FOS: Physical sciences, General Relativity and Quantum Cosmology (gr-qc), Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), General Relativity and Quantum Cosmology, cosmological parameters, quasar absorption systems, methods: observational, techniques: spectroscopic, Astrophysics - Cosmology and Nongalactic Astrophysics
Abstract

Recent advances in spectroscopic instrumentation and calibration methods dramatically improve the quality of quasar spectra. Supercomputer calculations show that, at high spectral resolution, procedures used in some previous analyses of spacetime variations of fundamental constants are likely to generate spurious measurements, biased systematically towards a null result. Developments in analysis methods are also summarised and a prescription given for the analysis of new and forthcoming data., 17 pages, 6 figures, accepted for publication in "The Universe". Contribution for the AlteCosmoFun'21 conference volume, 6-10 September 2022, Szczecin, Poland

Published
2022
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66. Cosmology intertwined: A review of the particle physics, astrophysics, and cosmology associated with the cosmological tensions and anomalies

Author

Abdalla, Elcio, primary, Abellán, Guillermo Franco, additional, Aboubrahim, Amin, additional, Agnello, Adriano, additional, Akarsu, Özgür, additional, Akrami, Yashar, additional, Alestas, George, additional, Aloni, Daniel, additional, Amendola, Luca, additional, Anchordoqui, Luis A., additional, Anderson, Richard I., additional, Arendse, Nikki, additional, Asgari, Marika, additional, Ballardini, Mario, additional, Barger, Vernon, additional, Basilakos, Spyros, additional, Batista, Ronaldo C., additional, Battistelli, Elia S., additional, Battye, Richard, additional, Benetti, Micol, additional, Benisty, David, additional, Berlin, Asher, additional, de Bernardis, Paolo, additional, Berti, Emanuele, additional, Bidenko, Bohdan, additional, Birrer, Simon, additional, Blakeslee, John P., additional, Boddy, Kimberly K., additional, Bom, Clecio R., additional, Bonilla, Alexander, additional, Borghi, Nicola, additional, Bouchet, François R., additional, Braglia, Matteo, additional, Buchert, Thomas, additional, Buckley-Geer, Elizabeth, additional, Calabrese, Erminia, additional, Caldwell, Robert R., additional, Camarena, David, additional, Capozziello, Salvatore, additional, Casertano, Stefano, additional, Chen, Geoff C.-F., additional, Chluba, Jens, additional, Chen, Angela, additional, Chen, Hsin-Yu, additional, Chudaykin, Anton, additional, Cicoli, Michele, additional, Copi, Craig J., additional, Courbin, Fred, additional, Cyr-Racine, Francis-Yan, additional, Czerny, Bożena, additional, Dainotti, Maria, additional, D'Amico, Guido, additional, Davis, Anne-Christine, additional, de Cruz Pérez, Javier, additional, de Haro, Jaume, additional, Delabrouille, Jacques, additional, Denton, Peter B., additional, Dhawan, Suhail, additional, Dienes, Keith R., additional, Di Valentino, Eleonora, additional, Du, Pu, additional, Eckert, Dominique, additional, Escamilla-Rivera, Celia, additional, Ferté, Agnès, additional, Finelli, Fabio, additional, Fosalba, Pablo, additional, Freedman, Wendy L., additional, Frusciante, Noemi, additional, Gaztañaga, Enrique, additional, Giarè, William, additional, Giusarma, Elena, additional, Gómez-Valent, Adrià, additional, Handley, Will, additional, Harrison, Ian, additional, Hart, Luke, additional, Hazra, Dhiraj Kumar, additional, Heavens, Alan, additional, Heinesen, Asta, additional, Hildebrandt, Hendrik, additional, Hill, J. Colin, additional, Hogg, Natalie B., additional, Holz, Daniel E., additional, Hooper, Deanna C., additional, Hosseininejad, Nikoo, additional, Huterer, Dragan, additional, Ishak, Mustapha, additional, Ivanov, Mikhail M., additional, Jaffe, Andrew H., additional, Jang, In Sung, additional, Jedamzik, Karsten, additional, Jimenez, Raul, additional, Joseph, Melissa, additional, Joudaki, Shahab, additional, Kamionkowski, Marc, additional, Karwal, Tanvi, additional, Kazantzidis, Lavrentios, additional, Keeley, Ryan E., additional, Klasen, Michael, additional, Komatsu, Eiichiro, additional, Koopmans, Léon V.E., additional, Kumar, Suresh, additional, Lamagna, Luca, additional, Lazkoz, Ruth, additional, Lee, Chung-Chi, additional, Lesgourgues, Julien, additional, Levi Said, Jackson, additional, Lewis, Tiffany R., additional, L'Huillier, Benjamin, additional, Lucca, Matteo, additional, Maartens, Roy, additional, Macri, Lucas M., additional, Marfatia, Danny, additional, Marra, Valerio, additional, Martins, Carlos J.A.P., additional, Masi, Silvia, additional, Matarrese, Sabino, additional, Mazumdar, Arindam, additional, Melchiorri, Alessandro, additional, Mena, Olga, additional, Mersini-Houghton, Laura, additional, Mertens, James, additional, Milaković, Dinko, additional, Minami, Yuto, additional, Miranda, Vivian, additional, Moreno-Pulido, Cristian, additional, Moresco, Michele, additional, Mota, David F., additional, Mottola, Emil, additional, Mozzon, Simone, additional, Muir, Jessica, additional, Mukherjee, Ankan, additional, Mukherjee, Suvodip, additional, Naselsky, Pavel, additional, Nath, Pran, additional, Nesseris, Savvas, additional, Niedermann, Florian, additional, Notari, Alessio, additional, Nunes, Rafael C., additional, Ó Colgáin, Eoin, additional, Owens, Kayla A., additional, Özülker, Emre, additional, Pace, Francesco, additional, Paliathanasis, Andronikos, additional, Palmese, Antonella, additional, Pan, Supriya, additional, Paoletti, Daniela, additional, Perez Bergliaffa, Santiago E., additional, Perivolaropoulos, Leandros, additional, Pesce, Dominic W., additional, Pettorino, Valeria, additional, Philcox, Oliver H.E., additional, Pogosian, Levon, additional, Poulin, Vivian, additional, Poulot, Gaspard, additional, Raveri, Marco, additional, Reid, Mark J., additional, Renzi, Fabrizio, additional, Riess, Adam G., additional, Sabla, Vivian I., additional, Salucci, Paolo, additional, Salzano, Vincenzo, additional, Saridakis, Emmanuel N., additional, Sathyaprakash, Bangalore S., additional, Schmaltz, Martin, additional, Schöneberg, Nils, additional, Scolnic, Dan, additional, Sen, Anjan A., additional, Sehgal, Neelima, additional, Shafieloo, Arman, additional, Sheikh-Jabbari, M.M., additional, Silk, Joseph, additional, Silvestri, Alessandra, additional, Skara, Foteini, additional, Sloth, Martin S., additional, Soares-Santos, Marcelle, additional, Solà Peracaula, Joan, additional, Songsheng, Yu-Yang, additional, Soriano, Jorge F., additional, Staicova, Denitsa, additional, Starkman, Glenn D., additional, Szapudi, István, additional, Teixeira, Elsa M., additional, Thomas, Brooks, additional, Treu, Tommaso, additional, Trott, Emery, additional, van de Bruck, Carsten, additional, Vazquez, J. Alberto, additional, Verde, Licia, additional, Visinelli, Luca, additional, Wang, Deng, additional, Wang, Jian-Min, additional, Wang, Shao-Jiang, additional, Watkins, Richard, additional, Watson, Scott, additional, Webb, John K., additional, Weiner, Neal, additional, Weltman, Amanda, additional, Witte, Samuel J., additional, Wojtak, Radosław, additional, Yadav, Anil Kumar, additional, Yang, Weiqiang, additional, Zhao, Gong-Bo, additional, and Zumalacárregui, Miguel, additional

Published
2022
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77. Addendum: Precision in high resolution absorption line modelling, analytic Voigt derivatives, and optimisation methods

Author

Robert Carswell, John Webb, and Lee Chung-Chi

Subjects
Space and Planetary Science, Physics - Data Analysis, Statistics and Probability, FOS: Physical sciences, Astronomy and Astrophysics, Computational Physics (physics.comp-ph), Astrophysics - Instrumentation and Methods for Astrophysics, Instrumentation and Methods for Astrophysics (astro-ph.IM), Physics - Computational Physics, Data Analysis, Statistics and Probability (physics.data-an)
Abstract

The parent paper to this Addendum describes the optimisation theory on which VPFIT, a non-linear least-squares program for modelling absorption spectra, is based. In that paper, we show that Voigt function derivatives can be calculated analytically using Taylor series expansions and look-up tables, for the specific case of one column density parameter for each absorption component. However, in many situations, modelling requires more complex parameterisation, such as summed column densities over a whole absorption complex, or common pattern relative ion abundances. This Addendum provides those analytic derivatives., 4 pages, 2 figures. Submitted to MNRAS 23 Dec 2021, accepted 24 Dec 2021

Published
2021

92. Four direct measurements of the fine-structure constant 13 billion years ago

Author

Wilczynska, Michael R., primary, Webb, John K., additional, Bainbridge, Matthew, additional, Barrow, John D., additional, Bosman, Sarah E. I., additional, Carswell, Robert F., additional, Dąbrowski, Mariusz P., additional, Dumont, Vincent, additional, Lee, Chung-Chi, additional, Leite, Ana Catarina, additional, Leszczyńska, Katarzyna, additional, Liske, Jochen, additional, Marosek, Konrad, additional, Martins, Carlos J. A. P., additional, Milaković, Dinko, additional, Molaro, Paolo, additional, and Pasquini, Luca, additional

Published
2020
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