分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The exchange of a pair of neutrinos between two objects, seperated by a distance $r$, leads to a long-range effective potential proportional to $1/r_{}^5$, assuming massless neutrinos and four-fermion contact interactions. In this paper, we investigate how this known form of neutrino-mediated potentials might be altered if the distance $r$ is sufficiently short, corresponding to a sufficiently large momentum transfer which could invalidate the contact interactions. We consider two possible scenarios to open up the contact interactions by introducing a $t$-channel or an $s$-channel mediator. We derive a general formula that is valid to describe the potential in all regimes as long as the external particles remain non-relativistic. In both scenarios, the potential decreases as $1/r_{}^5$ in the long-range limit as expected. In the short-range limit, the $t$-channel potential exhibits the Coulomb-like behavior (i.e. proportional to $1/r$), while the $s$-channel potential exhibits $1/r_{}^4$ and $1/r_{}^2$ behaviors.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Right-handed neutrinos (RHNs) provide a natural portal to a dark sector accommodating dark matter (DM). In this work, we consider that the dark sector is connected to the standard model only via RHNs and ask how DM can be produced from RHNs. Our framework concentrates on a rather simple and generic interaction that couples RHNs to a pair of dark particles. Depending on whether RHNs are light or heavy in comparison to the dark sector and also on whether one or both of them are in the freeze-in/out regime, there are many distinct scenarios resulting in rather different results. We conduct a comprehensive and systematic study of all possible scenarios in this paper. For illustration, we apply our generic results to the type-I seesaw model with the dark sector extension, addressing whether and when DM in this model can be in the freeze-in or freeze-out regime. Some observational consequences in this framework are also discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Right-handed neutrinos (RHNs) provide a natural portal to a dark sector accommodating dark matter (DM). In this work, we consider that the dark sector is connected to the standard model only via RHNs and ask how DM can be produced from RHNs. Our framework concentrates on a rather simple and generic interaction that couples RHNs to a pair of dark particles. Depending on whether RHNs are light or heavy in comparison to the dark sector and also on whether one or both of them are in the freeze-in/out regime, there are many distinct scenarios resulting in rather different results. We conduct a comprehensive and systematic study of all possible scenarios in this paper. For illustration, we apply our generic results to the type-I seesaw model with the dark sector extension, addressing whether and when DM in this model can be in the freeze-in or freeze-out regime. Some observational consequences in this framework are also discussed.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the early universe, Dirac neutrino magnetic moments due to their chirality-flipping nature could lead to thermal production of right-handed neutrinos, which would make a significant contribution to the effective neutrino number, $N_{\rm eff}$. We present in this paper a dedicated computation of the neutrino chirality-flipping rate in the thermal plasma. With a careful and consistent treatment of soft scattering and the plasmon effect in finite temperature field theories, we find that neutrino magnetic moments above $2.7\times 10^{-12}\mu_B$ have been excluded by current CMB and BBN measurements of $N_{\rm eff}$, assuming flavor-universal and diagonal magnetic moments for all three generation of neutrinos. This limit is stronger than the latest bounds from XENONnT and LUX-ZEPLIN experiments, and comparable with those from stellar cooling considerations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a free, intensive, rarely interactive and well directional messenger, solar neutrinos have been driving both solar physics and neutrino physics developments for more than half a century. Since more extensive and advanced neutrino experiments are under construction, being planned or proposed, we are striving toward an era of precise and comprehensive measurement of solar neutrinos in the next decades. In this article, we review recent theoretical and experimental progress achieved in solar neutrino physics. We present not only an introduction to neutrinos from the standard solar model and the standard flavor evolution, but also a compilation of a variety of new physics that could affect and hence be probed by solar neutrinos. After reviewing the latest techniques and issues involved in the measurement of solar neutrino spectra and background reduction, we provide our anticipation on the physics gains from the new generation of neutrino experiments.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： As a free, intensive, rarely interactive and well directional messenger, solar neutrinos have been driving both solar physics and neutrino physics developments for more than half a century. Since more extensive and advanced neutrino experiments are under construction, being planned or proposed, we are striving toward an era of precise and comprehensive measurement of solar neutrinos in the next decades. In this article, we review recent theoretical and experimental progress achieved in solar neutrino physics. We present not only an introduction to neutrinos from the standard solar model and the standard flavor evolution, but also a compilation of a variety of new physics that could affect and hence be probed by solar neutrinos. After reviewing the latest techniques and issues involved in the measurement of solar neutrino spectra and background reduction, we provide our anticipation on the physics gains from the new generation of neutrino experiments.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the early universe, Dirac neutrino magnetic moments due to their chirality-flipping nature could lead to thermal production of right-handed neutrinos, which would make a significant contribution to the effective neutrino number, $N_{\rm eff}$. We present in this paper a dedicated computation of the neutrino chirality-flipping rate in the thermal plasma. With a careful and consistent treatment of soft scattering and the plasmon effect in finite temperature field theories, we find that neutrino magnetic moments above $2.7\times 10^{-12}\mu_B$ have been excluded by current CMB and BBN measurements of $N_{\rm eff}$, assuming flavor-universal and diagonal magnetic moments for all three generation of neutrinos. This limit is stronger than the latest bounds from XENONnT and LUX-ZEPLIN experiments, and comparable with those from stellar cooling considerations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The Standard Model predicts a long-range force, proportional to $G_F^2/r^5$, between fermions due to the exchange of a pair of neutrinos. This quantum force is feeble and has not been observed yet. In this paper, we compute this force in the presence of neutrino backgrounds, both for isotropic and directional background neutrinos. We find that for the case of directional background the force can have a $1/r$ dependence and it can be significantly enhanced compared to the vacuum case. In particular, background effects caused by reactor, solar, and supernova neutrinos enhance the force by many orders of magnitude. The enhancement, however, occurs only in the direction parallel to the direction of the background neutrinos. We discuss the experimental prospects of detecting the neutrino force in neutrino backgrounds and find that the effect is close to the available sensitivity of the current fifth force experiments. Yet, the angular spread of the neutrino flux and that of the test masses reduce the strength of this force. The results are encouraging and a detailed experimental study is called for to check if the effect can be probed.
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