分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要：In this paper, we present a systematic investigation on simple inverse seesaw models for neutrino masses and flavor mixing based on the modular $S^{}_4$ symmetry. Two right-handed neutrinos and three extra fermion singlets are introduced to account for light neutrino masses through the inverse seesaw mechanism, and to provide a keV-mass sterile neutrino as the candidate for warm dark matter in our Universe. Considering all possible modular forms with weights no larger than four, we obtain twelve models, among which we find one is in excellent agreement with the observed lepton mass spectra and flavor mixing. Moreover, we explore the allowed range of the sterile neutrino mass and mixing angles, by taking into account the direct search of $X$-ray line and the Lyman-$\alpha$ observations. The model predictions for neutrino mixing parameters and the dark matter abundance will be readily testable in future neutrino oscillation experiments and cosmological observations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要：We consider a modified gravity framework for inflation by adding to the Einstein-Hilbert action a direct $f(\phi)T$ term, where $\phi$ is identified as the inflaton and $T$ is the trace of the energy-momentum tensor. The framework goes to Einstein gravity naturally when the inflaton decays out. We investigate inflation dynamics in this $f(\phi)T$ gravity (not to be confused with torsion-scalar coupled theories) on a general basis and then apply it to three well-motivated inflationary models. We find that the predictions for the spectral tilt and the tensor-to-scalar ratio are sensitive to this new $f(\phi)T$ term. This $f(\phi)T$ gravity brings chaotic and natural inflation into better agreement with data and allows a larger tensor-to-scalar ratio in the Starobinsky model.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Chen Jiang
Tao Wu
Adina D. Feinstein
Keivan G. Stassun
Timothy R. Bedding
Dimitri Veras
Enrico Corsaro
Derek L. Buzasi
Dennis Stello
Yaguang Li
Savita Mathur
Rafael A. Garcia
Sylvain N. Breton
Mia S. Lundkvist
Przemyslaw J. Mikolajczyk
Charlotte Gehan
Tiago L. Campante
Diego Bossini
Stephen R. Kane
Jia Mian Joel Ong
摘要：The Transiting Exoplanet Survey Satellite (TESS) mission searches for new exoplanets. The observing strategy of TESS results in high-precision photometry of millions of stars across the sky, allowing for detailed asteroseismic studies of individual systems. In this work, we present a detailed asteroseismic analysis of the giant star HD 76920 hosting a highly eccentric giant planet ($e = 0.878$) with an orbital period of 415 days, using 5 sectors of TESS light curve that cover around 140 days of data. Solar-like oscillations in HD 76920 are detected around $52 \, \mu$Hz by TESS for the first time. By utilizing asteroseismic modeling that takes classical observational parameters and stellar oscillation frequencies as constraints, we determine improved measurements of the stellar mass ($1.22 \pm 0.11\, M_\odot$), radius ($8.68 \pm 0.34\,R_\odot$), and age ($5.2 \pm 1.4\,$Gyr). With the updated parameters of the host star, we update the semi-major axis and mass of the planet as $a=1.165 \pm 0.035$ au and $M_{\rm p}\sin{i} = 3.57 \pm 0.22\,M_{\rm Jup}$. With an orbital pericenter of $0.142 \pm 0.005$ au, we confirm that the planet is currently far away enough from the star to experience negligible tidal decay until being engulfed in the stellar envelope. We also confirm that this event will occur within about 100\,Myr, depending on the stellar model used.
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