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Register a new userResidual proton-neutron interactions and the $N_{rm p} N_{rm n}$ scheme
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We investigate the correlation between integrated proton-neutron interactions obtained by using the up-to-date experimental data of binding energies and the $N_{rm p} N_{rm n}$, the product of valence proton number and valence neutron number with respect to the nearest doubly closed nucleus. We make corrections on a previously suggested formula for the integrated proton-neutron interaction. Our results demonstrate a nice, nearly linear, correlation between the integrated p-n interaction and $N_{rm p} N_{rm n}$, which provides us with a firm foundation of the applicability of the $N_{rm p} N_{rm n}$ scheme to nuclei far from the stability line.
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If neutrinos are Dirac particles the existence of light right-handed neutrinos $ u_{R}$ is implied. Those would contribute to the effective number of relativistic neutrino species $N_{{rm eff}}$ in the early Universe. With pure standard model interactions, the contribution is negligibly small. In the presence of new interactions, however, the contribution could be significantly enhanced. We consider the most general effective four-fermion interactions for neutrinos (scalar, pseudo-scalar, vector, axial-vector and tensor), and compute the contribution of right-handed neutrinos to $N_{{rm eff}}$. Taking the Planck 2018 measurement of $N_{{rm eff}}$, strong constraints on the effective four-fermion coupling are obtained, corresponding to interaction strengths of $10^{-5}sim10^{-3}$ in units of the Fermi constant. This translates in new physics scales of up to 43 TeV and higher. Future experiments such as CMB-S4 can probe or exclude the existence of effective 4-neutrino operators for Dirac neutrinos. Ways to avoid this conclusion are discussed.
A new U(1) gauge symmetry is the simplest extension of the Standard Model and has various theoretical and phenomenological motivations. In this paper, we study the cosmological constraint on the MeV scale dark photon. After the neutrino decoupling era at $T = mathcal{O}(1),$MeV, the decay and annihilation of the dark photon heats up the electron and photon plasma and accordingly decreases the effective number of neutrino $N_{mathrm{eff}}$ in the recombination era. We derive a conservative lower-limit of the dark photon mass around 8.5 MeV from the current Planck data if the mixing between the dark photon and ordinary photon is larger than $mathcal{O}(10^{-9})$. We also find that the future CMB stage-$rm I! V$ experiments can probe up to 17 MeV dark photon.
We investigate whether the $4.4sigma$ tension on $H_0$ between SH$_{0}$ES 2019 and Planck 2018 can be alleviated by a variation of Newtons constant $G_N$ between the early and the late Universe. This changes the Hubble rate before recombination, similarly to adding $Delta N_{rm eff}$ extra relativistic degrees of freedom. We implement a varying $G_N$ in a scalar-tensor theory of gravity, with a non-minimal coupling $(M^2+beta phi^2)R$. If the scalar $phi$ starts in the radiation era at an initial value $phi_I sim 0.5~M_p$ and with $beta<0$, a dynamical transition occurs naturally around the epoch of matter-radiation equality and the field evolves towards zero at late times. As a consequence, the $H_0$ tension between SH$_{0}$ES (2019) and Planck 2018+BAO slightly decreases, as in $Delta N_{rm eff}$ models, to the 3.8$sigma$ level. We then perform a fit to a combined Planck, BAO and supernovae (SH$_0$ES and Pantheon) dataset. When including local constraints on Post-Newtonian (PN) parameters, we find $H_0=69.08_{-0.71}^{+0.6}~text{km/s/Mpc}$ and a marginal improvement of $Deltachi^2simeq-3.2$ compared to $Lambda$CDM, at the cost of 2 extra parameters. In order to take into account scenarios where local constraints could be evaded, we also perform a fit without PN constraints and find $H_0=69.65_{-0.78}^{+0.8}~text{km/s/Mpc}$ and a more significant improvement $Deltachi^2=-5.4$ with 2 extra parameters. For comparison, we find that the $Delta N_{rm eff}$ model gives $H_0=70.08_{-0.95}^{+0.91}~text{km/s/Mpc}$ and $Deltachi^2=-3.4$ at the cost of one extra parameter, which disfavors the $Lambda$CDM limit just above 2$sigma$, since $Delta N_{rm eff}=0.34_{-0.16}^{+0.15}$. Overall, our varying $G_N$ model performs similarly to the $Delta N_{rm eff}$ model in respect to the $H_0$ tension, if a physical mechanism to remove PN constraints can be implemented.
We discuss Dirac neutrinos whose right-handed component $ u_R$ has new interactions that may lead to a measurable contribution to the effective number of relativistic neutrino species $N_{rm eff}$. We aim at a model-independent and comprehensive study on a variety of possibilities. Processes for $ u_R$-genesis from decay or scattering of thermal species, with spin-0, spin-1/2, or spin-1 initial or final states are all covered. We calculate numerically and analytically the contribution of $ u_R$ to $N_{rm eff}$ primarily in the freeze-in regime, since the freeze-out regime has been studied before. While our approximate analytical results apply only to freeze-in, our numerical calculations work for freeze-out as well, including the transition between the two regimes. Using current and future constraints on $N_{rm eff}$, we obtain limits and sensitivities of CMB experiments on masses and couplings of the new interactions. As a by-product, we obtain the contribution of Higgs-neutrino interactions, $Delta N_{rm eff}^{rm SM} approx 7.5times10^{-12}$, assuming the neutrino mass is 0.1 eV and generated by the standard Higgs mechanism.
We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio $G^{n}_{E}/G^{n}_{M}$ was extracted from the beam-target vector asymmetry $A_{ed}^{V}$ at four-momentum transfers $Q^{2}=0.14$, 0.20, 0.29 and 0.42 (GeV/c)$^{2}$.
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