A system of classical interacting spins can develop collective instabilities, which, in the nonlinear regime, mimic the motion of a gyroscopic pendulum. Known as the flavor pendulum, this behavior appears among the collective modes of a dense neutrino plasma after a strong reduction of phase space through symmetry assumptions. It has been identified in homogeneous slow and fast flavor systems and, most recently, in single-wave solutions of the fast system. For the first time, we explain the reasons for its ubiquitous appearance. We show that a system of three classical spins must always be pendular, or only two in the presence of an external field. Furthermore, such a system always defines a continuum of vectors with time-independent length. If these are identified as interacting spins, they immediately lead to the continuum cases of slow and fast flavor pendula. As another new insight, any of these spins can be chosen as the pendulum, periodically exchanging flavor with the rest of the system.
Standard-Model (SM) hadronic parton showers initiated by secondary cosmic-ray production or dark matter (DM) annihilations robustly predict very low antinuclei yields and a strong additional suppression for heavier antinuclei. We show that an important exception can arise if DM annihilates into a confining dark sector that produces soft unclustered energy patterns (SUEPs). The hallmark of SUEPs is the emission of very large multiplicities of soft dark mesons (pi D), which can overcome the usual phase-space suppression of antinuclei formation in parton showers, provided that the dark mesons decay promptly into SM quarks, i.e., within a SM hadronization length. We study several benchmark realizations and find that for DM masses mDM O(10 TeV), dark meson masses m pi D 400 GeV, pi D dominantly decaying to tt & strns;, and a SUEP temperature TSUEP <^> 0.1m pi D, DM annihilation into SUEPs can yield tens of antideuterons and a few antihelium-3 events at AMS - 02 at kinetic energies of O(GeV/n) and a few antideuterons and antihelium-3 events in GAPS at energies below 0.5 GeV/n. A future confirmation of an antinuclei signal by the AMS - 02 or GAPS experiments could provide hints for hidden confining dynamics and would significantly constrain the relevant SUEP parameters.
We perform dimensional reduction of the dimension-6 standard model effective field theory (SMEFT) to order g4 in coupling constants g. This analysis includes one-loop contributions to kinetic terms and quartic couplings, as well as two-loop contributions, where operators such as four-fermion interactions first appear, to squared mass terms. Using lattice data, we provide evidence that, in contrast with previous statements in the literature, the SMEFT may undergo a first-order phase transition even for null j phi j6 at zero temperature-where phi is the Higgs doublet-opening the door to entirely unexplored directions in model building. In such case, however, our analysis implies that the phase transition is not sufficiently strong, narrowing down the new physics that allows for electroweak baryogenesis.
We compute the electromagnetic form factors of the proton and neutron using lattice QCD. We employ Nf = 2 + 1 + 1 twisted mass clover-improved fermions with quark masses tuned to their physical values. Three ensembles with lattice spacings of a = 0.080 fm, 0.068 fm, and 0.057 fm and approximately the same physical volume allow us to obtain the continuum limit directly at the physical pion mass. For each ensemble, we use several values of the sink-source time separation, ranging from 0.5 to 1.5 fm, to allow for a thorough analysis of excited-state effects via multistate fits. The disconnected contributions are also analyzed using high statistics combined with techniques to mitigate stochastic noise in the estimation of the fermion loop. These techniques include low-mode deflation, dilution in the color and spin components, and hierarchical probing. We study the momentum-transfer dependence of the form factors using the z-expansion and dipole Ans & auml;tze, thereby enabling the extraction of the electric and magnetic radii and the magnetic moments, as well as the Zemach and Friar radii in the continuum limit. Results for the proton and neutron electric and magnetic mean square radii are p ffiffiffiffiffiffiffiffiffiffiffi p ffiffiffiffiffiffiffiffiffiffiffi (r2 E)n = -0.147(48) fm2, (r2 M)p = 0.870(53)(15) fm, and (r2M)n = 0.913(67)(19) fm, and for the proton and neutron magnetic moments, mu p = 2.849(92)(52) and mu n= -1.819(76)(29), respectively. In all cases, the first error is statistical, and the second is systematic, where the latter includes an estimate of the error from the fits to the momentum dependence of the form factors and from the continuum extrapolation.
Using (2.712 +/- 0.014) x 10(9) psi(3686) events collected with the BESIII detector at the BEPCII collider, we report an evidence of Xi(0) transverse polarization with a significance of 4.4 sigma, a precise measurement of the branching fraction and the ratios between the S-wave and D-wave contributions of psi(3686) -> Xi(0)(Xi) over bar (0). The weak decay parameters (phi(Xi 0/(Xi) over bar)0, alpha(Xi 0/(Xi) over bar0)) and the angular distribution (alpha(psi)) are also measured with higher precision compared to the previous measurements. Furthermore, two the CP observables are also determined to be A(CP)(Xi 0) = -0.014 +/- 0.030 +/- 0.010 and Delta phi(Xi 0)(CP) = 0.000 +/- 0.028 +/- 0.003 rad, which are still consistent with CP conservation at 1 sigma level under the current statistics.
