分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Nieh-Yan modified teleparallel gravity is a model which modifies the general relativity equivalent teleparallel gravity by a coupling between the Nieh-Yan density and an axion-like field. This model predicts parity violations in the gravitational waves if the axion-like field has a non-trivial background, and more importantly it is ghost free and avoids the pathologies presented in other parity-violating gravity models. The cosmological dynamics and perturbations of the Nieh-Yan modified teleparallel gravity have been investigated in detail, but all these previous investigations rely on the symmetry requirement that in the background universe both the metric and affine connection are homogeneous and isotropic. In this paper we relax the symmetry constraint on the connection and leave it arbitrary at the beginning, after all the cosmological principle only needs the metric of the background spacetime to meet the symmetry requirement. We find a new flat universe solution for the Nieh-Yan modified teleparallel gravity, for which the background dynamics itself is unchanged but the perturbations around it present a new feature that the scalar and tensor perturbations are coupled together at the linear level. The implications of this peculiar feature in primordial perturbations from inflation are also discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper, we consider the possibilities of generating baryon number asymmetry in thermal equilibrium within the frameworks of teleparallel and symmetric teleparallel gravities. Through the derivative couplings of the torsion scalar or the non-metricity scalar to baryons, the baryon number asymmetry is indeed produced in the radiation dominated epoch. For gravitational baryogenesis mechanisms in these two frameworks, the produced baryon-to-entropy ratio is too small to be consistent with observations. But the gravitational leptogenesis models within both frameworks have the possibilities to interpret the observed baryon-antibaryon asymmetry.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In this paper we consider the parity violating gravity model within the framework of teleparallel gravity. The parity violations are caused by the couplings of a scalar field to the scalar invariants which are parity-odd and quadratic in the torsion tensor. Totally there are two such type independent invariants, and one of them is the Nieh-Yan density. Through investigations on the cosmological perturbations of this model, we find that in general it suffers from the difficulties of ghost instability in the scalar and vector perturbations. But in the special case only the coupling to the Nieh-Yan density exists, this model is ghost free and reduces to the Nieh-Yan modified Teleparallel Gravity model. We also analyze the severity of the ghost instability by studying the perturbations around the Minkowski background.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Many parity violating gravity models suffer from the ghost instability problem. In this paper, we consider a symmetric teleparallel gravity model that extends the general relativity equivalent model by several parity violating interactions between the gravitational field and a scalar field. These interactions exclude higher derivatives and are quadratic in the nonmetricity tensor. Through investigations on the linear cosmological perturbations, our results show that, in general, this model suffers from the difficulty caused by the existence of ghost mode in the vector perturbations. However, in cases where a special condition is imposed on the coefficients of these parity violating interactions, this model can be ghost free.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The parity violating gravity models based on the symmetric teleparallel gravity have been considered in the literature, but their applications in cosmology and especially the modifications to cosmological perturbations have not been fully explored. In this paper we consider such a simple model which modifies general relativity by a parity non-conserved coupling, within the framework of the symmetric teleparallel gravity. We study in detail its cosmological applications and focus on its cosmological perturbation theory. Besides the already known parity violation in the tensor perturbations, we find that the vector perturbations in this model are promoted to be dynamical degrees of freedom, and the left- and right-handed vector modes propagate with different velocities. More importantly, we find that one of the vector modes is a ghost at high momentum scales, which will give rise to the problem of vacuum instability in the quantum theory of cosmological perturbations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Recently, based on the theory of teleparallel gravity, a simple and ghost free parity violating gravity model was proposed in [M. Li, H. Rao, and D. Zhao, J. Cosmol. Astropart. Phys. 11 (2020) 023], where the Weitzenb\"{o}ck connection was adopted for simplifying the calculations but breaks the local Lorentz symmetry explicitly. In this paper, we restore the local Lorentz symmetry of this model by giving up the Weitzenb\"{o}ck condition on the spin connection. With full local Lorentz covariance, this model is not a pure tetrad theory any more. We also apply the new version of this model to the universe with general Friedmann-Robertson-Walker background. This further generalizes the studies of [M. Li, H. Rao, and D. Zhao, J. Cosmol. Astropart. Phys. 11 (2020) 023] where only the spatially flat background was considered. Through the investigations of this paper, we confirm the results obtained in [M. Li, H. Rao, and D. Zhao, J. Cosmol. Astropart. Phys. 11 (2020) 023] and in addition get some new results.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Nieh-Yan modified teleparallel gravity is a model which modifies the general relativity equivalent teleparallel gravity by a coupling between the Nieh-Yan density and an axion-like field. This model predicts parity violations in the gravitational waves if the axion-like field has a non-trivial background, and more importantly it is ghost free and avoids the pathologies presented in other parity-violating gravity models. The cosmological dynamics and perturbations of the Nieh-Yan modified teleparallel gravity have been investigated in detail, but all these previous investigations rely on the symmetry requirement that in the background universe both the metric and affine connection are homogeneous and isotropic. In this paper we relax the symmetry constraint on the connection and leave it arbitrary at the beginning, after all the cosmological principle only needs the metric of the background spacetime to meet the symmetry requirement. We find a new flat universe solution for the Nieh-Yan modified teleparallel gravity, for which the background dynamics itself is unchanged but the perturbations around it present a new feature that the scalar and tensor perturbations are coupled together at the linear level. The implications of this peculiar feature in primordial perturbations from inflation are also discussed.
分类： 物理学 >> 普通物理:统计和量子力学,量子信息等 提交时间： 2017-11-10
Hong Li
Si-Yu Li
Yang Liu
Yong-Ping Li
Yifu Cai
Mingzhe Li
Gong-Bo
Zhao
Cong-Zhan Liu
Zheng-Wei Li
He Xu
Di Wu
Yong-Jie Zhang
Zu-Hui
Fan
Yong-Qiang Yao
Chao-Lin Kuo
Fang-Jun Lu
Xinmin Zhang
摘要： In this paper, we will give a general introduction to the project of Ali CMB Polarization Tele-scope (AliCPT), which is a Sino-US joint project led by the Institute of High Energy Physics (IHEP) and has involved many di erent institutes in China. It is the rst ground-based cosmic microwave background (CMB) polarization experiment in China and an integral part of China's Gravitational Waves Program. The main scienti c goal of AliCPT project is to probe the primor-dial gravitational waves (PGWs) originated from the very early Universe. The AliCPT project includes two stages. The rst stage referred to as AliCPT-1, is to build a telescope in the Ali region of Tibet with an altitude of 5,250 meters. Once completed, it will be the worldwide highest ground-based CMB observatory and open a new window for probing PGWs in northern hemisphere. AliCPT-1 telescope is designed to have about 7,000 TES detectors at 90GHz and 150GHz. The second stage is to have a more sensitive telescope (AliCPT-2) with the number of detectors more than 20,000. Our simulations show that AliCPT will improve the current constraint on the tensor-to-scalar ratio r by one order of magnitude with 3 years' observation. Besides the PGWs, the AliCPT will also enable a precise measurement on the CMB rotation angle and provide a precise test on the CPT symmetry. We show 3 years' observation will improve the current limit by two order of magnitude.
分类： 生物学 >> 植物学 >> 植物生物化学、植物生物物理学 提交时间： 2016-05-03
摘要： >Flowering is a highly orchestrated and extremely critical process in a plant's life cycle. Previous study has demonstrated that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) and FLOWERING LOCUS T (FT) integrate the gibberellic acid (GA) signaling pathway and vernalization pathway in regulating flowering time, but detailed molecular mechanisms remain largely unclear. In GA signaling pathway, DELLA proteins are a group of master transcriptional regulators, while in vernalization pathway FLOWERING LOCUS C (FLC) is a core transcriptional repressor that down-regulates the expression of SOC1 and FT. Here, we report that DELLA proteins interact with FLC in vitro and in vivo, and the LHRI domains of DELLAs and the C-terminus of MADS domain of FLC are required for these interactions. Phenotypic and gene expression analysis showed that mutation of FLC reduces while over-expression of FLC enhances the GA response in the flowering process. Further, DELLA-FLC interactions promote the repression ability of FLC on its target genes. In summary, these findings report that the interaction between MADS box transcription factor FLC and GRAS domain regulator DELLAs may integrate various signaling inputs in flowering time control, and shed new light on the regulatory mechanism both for FLC and DELLAs in regulating gene expression.
点击量
待评议
点击量
下载量
评论
