Connected formulas for amplitudes in standard model

Witten's twistor string theory has led to new representations of S-matrix in massless QFT as a single object, including Cachazo-He-Yuan formulas in general and connected formulas in four dimensions. As a first step towards more realistic processes of the standard model, we extend the construction to QCD tree amplitudes with massless quarks and those with a Higgs boson. For both cases, we find connected formulas in four dimensions for all multiplicities which are very similar to the one for Yang-Mills amplitudes. The formula for quark-gluon color-ordered amplitudes differs from the pure-gluon case only by a Jacobian factor that depends on flavors and orderings of the quarks. In the formula for Higgs plus multi-parton amplitudes, the massive Higgs boson is effectively described by two additional massless legs which do not appear in the Parke-Taylor factor. The latter also represents the first twistor-string/connected formula for form factors.Comment: 18 pages, 3 figure

A protocol of potential advantage in the low frequency range to gravitational wave detection with space based optical atomic clocks

A recent proposal describes space based gravitational wave (GW) detection with optical lattice atomic clocks [Kolkowitz et. al., Phys. Rev. D 94, 124043 (2016)] [1]. Based on their setup, we propose a new measurement method for gravitational wave detection in low frequency with optical lattice atomic clocks. In our method, n successive Doppler signals are collected and the summation for all these signals is made to improve the sensitivity of the low-frequency GW detection. In particular, the improvement is adjustable by the number of Doppler signals, which is equivalent to that the length between two atomic clocks is increased. Thus, the same sensitivity can be reached but with shorter distance, even though the acceleration noises lead to failing to achieve the anticipated improvement below the inflection point of frequency which is determined by the quantum projection noise. Our result is timely for the ongoing development of space-born observatories aimed at studying physical and astrophysical effects associated with low-frequency GW

Exotic Charges, Multicomponent Dark Matter and Light Sterile Neutrinos

Generating small sterile neutrino masses via the same seesaw mechanism that suppresses active neutrino masses requires a specific structure in the neutral fermion mass matrix. We present a model where this structure is enforced by a new U(1)' gauge symmetry, spontaneously broken at the TeV scale. In order not to spoil the neutrino structure, the additional fermions necessary for anomaly cancellations need to carry exotic charges, and turn out to form multicomponent cold dark matter. The active-sterile mixing then connects the new particles and the Standard Model---opening a new portal in addition to the usual Higgs- and kinetic-mixing portals---which leads to dark matter annihilation almost exclusively into neutrinos.Comment: 11 pages, 3 figures. More references, longer discussions. Matches JHEP versio

Domain of attraction of quasi-stationary distribution for one-dimensional diffusions

We study quasi-stationarity for one-dimensional diffusions killed at 0, when 0 is a regular boundary and $+\infty$ is an entrance boundary. We give a necessary and sufficient condition for the existence of exactly one quasi-stationary distribution, and we also show that this distribution attracts all initial distributions.Comment: This paper is published in Frontiers of Mathematics in China (2016

Modelling the number counts of early-type galaxies by pure luminosity evolution

In this paper, we explore the plausible luminosity evolution of early-type galaxies in different cosmological models by constructing a set of pure luminosity evolution (PLE) models via the choices of the star formation rate (SFR) parameters and formation redshift $z_f$ of galaxies, with the observational constraints derived from the Hubble Space Telescope (HST) morphological number counts for elliptical and S0 galaxies of the Medium Deep Survey (MDS) and the Hubble Deep Field (HDF). We find that the number counts of early-type galaxies can be explained by the pure luminosity evolution models, without invoking exotic scenarios such as merging or introducing an additional population. But the evolution should be nearly passive, with a high $z_f$ assumed. The conclusion is valid in all of the three cosmological models we adopted in this paper. We also present the redshift distributions for three bins of observed magnitudes in F814w pass-band, to show at which redshift are the objects that dominate the counts at a given magnitude. The predictions of the redshift distribution of $22.5<b_j<24.0$ are also presented for comparison with future data.Comment: Plain tex, 15pages, 9 eps figures, plus an extra figure fig2c.eps, with the tex-macro mn.tex. MNRAS, accepte