Hong-Jian He

Natural electroweak symmetry breaking from scale invariant Higgs mechanism

We construct a minimal viable extension of the standard model (SM) with classical scale symmetry. Its scalar sector contains a complex singlet in addition to the SM Higgs doublet. The scale-invariant and CP-symmetric Higgs potential generates radiative electroweak symmetry breaking ` a la Coleman-Weinberg, and gives a natural solution to the hierarchy problem, free from fine-tuning. Besides the 125 GeV SM-like Higgs particle, it predicts a new CP-even Higgs (serving as the pseudo-Nambu-Goldstone boson of scale symmetry breaking) and a CP-odd scalar singlet (providing the dark matter candidate) at weak scale. We systematically analyze experimental constraints from direct LHC Higgs searches and electroweak precision tests, as well as theoretical bounds from unitarity, triviality and vacuum stability. We demonstrate the viable parameter space, and discuss implications for new Higgs and dark matter (DM) searches at the upcoming LHC runs and for the on-going direct detections of DM.

CERN LHC signatures of new gauge bosons in the minimal Higgsless model

We study the LHC signatures of new gauge bosons in the gauge-invariant minimal Higgsless model. It predicts an extra pair of W{sub 1} and Z{sub 1} bosons which can be as light as {approx}400 GeV and play a key role in the delay of unitarity violation. We analyze the W{sub 1} signals in pp{yields}W{sub 0}Z{sub 0}Z{sub 0}{yields}jj4l and pp{yields}W{sub 0}Z{sub 0}jj{yields}{nu}3ljj processes at the LHC, including the complete electroweak and QCD backgrounds. We reveal the complementarity between these two channels for discovering the W{sub 1} boson, and demonstrate the LHC discovery potential over the full range of allowed W{sub 1} mass.

Common Origin of

We conjecture that all CP violations (both Dirac and Majorana types) arise from a common origin in the neutrino seesaw. With this conceptually attractive and simple conjecture, we deduce that mu-tau breaking shares the common origin with all CP violations. We study the common origin of mu-tau and CP breaking in the Dirac mass matrix of seesaw Lagrangian (with right-handed neutrinos being mu-tau blind), which uniquely leads to inverted mass ordering of light neutrinos. We then predict a very different correlation between the two small mu-tau breaking observables theta(13) - 0 degrees and theta(23) - 45 degrees, which can saturate the present experimental upper limit on theta(13). This will be tested against our previous normal mass-ordering scheme by the ongoing oscillation experiments. We also analyze the correlations of theta(13) with Jarlskog invariant and neutrinoless beta beta-decay observable. From the common origin of CP and mu-tau breaking in the neutrino seesaw, we establish a direct link between the low energy CP violations and the cosmological CP violation for baryon asymmetry. With these we further predict a lower bound on theta(13), supporting the ongoing probes of theta(13) at Daya Bay, Double Chooz, and RENO experiments. Finally, we analyze the general model-independent Z(2) circle times Z(2) symmetry structure of the light neutrino sector, and map it into the seesaw sector, where one of the Z(2)s corresponds to the mu-tau symmetry Z(2)(mu tau) and another the hidden symmetry Z(2)(s) (revealed in our previous work) which dictates the solar mixing angle theta(12). We derive the physical consequences of this Z(2)(s) and its possible partial violation in the presence of mu-tau breaking (with or without the neutrino seesaw), regarding the theta(12) determination and the correlation between mu-tau breaking observables.

\mu-\tau

In this note we examine the properties of deconstructed Higgsless models for the case of a fermion whose SU(2) properties arise from delocalization over many sites of the deconstructed lattice. We derive expressions for the correlation functions and use these to establish a generalized consistency relation among correlation functions. We discuss the form of the W boson wavefunction and show that if the probability distribution of the delocalized fermions is appropriately related to the W wavefunction, then deviations in precision electroweak parameters are minimized. In particular, we show that this ideal fermion delocalization results in the vanishing of three of the four leading zero-momentum electroweak parameters defined by Barbieri et al. We then discuss ideal fermion delocalization in the context of two continuum Higgsless models, one in Anti-deSitter space and one in flat space. Our results may be applied to any Higgsless linear moose model with multiple SU(2) groups, including those with only a few extra vector bosons.

and CP Breaking in Neutrino Seesaw, Baryon Asymmetry, and Hidden Flavor Symmetry

Abstract LHC Run-2 has provided intriguing di-photon signals of a new resonance around 750 GeV , which, if not due to statistical fluctuations, must call for new physics beyond the standard model (SM) at TeV scale. We propose a minimal extension of the SM with a complex singlet scalar S and a doublet of vector-like quarks. The scalar sector respects CP symmetry, with its CP-odd imaginary component χ providing a natural dark matter (DM) candidate. The real component of S serves as the new resonance ( 750 GeV ) and explains the diphoton excess of the LHC Run-2. The new scalar degrees of freedom of S help to stabilize the Higgs vacuum, and can realize the Higgs inflation around GUT scale, consistent with the current cosmological observations. We construct two representative samples A and B of our model for demonstration. We study the mono-jet signals of DM production from invisible decays Re ( S ) → χ χ at the LHC Run-2. We further derive the DM relic density bound, and analyze constraints from the direct and indirect DM detections.

Ideal fermion delocalization in Higgsless models

Neutrino oscillation data strongly support μ – τ symmetry as a good approximate flavor symmetry of the neutrino sector, which has to appear in any viable theory for neutrino mass-generation. The μ – τ breaking is not only small, but also the source of Dirac CP-violation. We conjecture that both discrete μ – τ and CP symmetries are fundamental symmetries of the seesaw Lagrangian (respected by interaction terms), and they are only softly broken, arising from a common origin via a unique dimension-3 Majorana mass-term of the heavy right-handed neutrinos. From this conceptually attractive and simple construction, we can predict the soft μ – τ breaking at low energies, leading to quantitative correlations between the apparently two small deviations θ23−45° and θ13−0°. This nontrivially connects the on-going measurements of mixing angle θ23 with the upcoming experimental probes of θ13. We find that any deviation of θ23−45° must put a lower limit on θ13. Furthermore, we deduce the low energy Dirac and Majorana CP violations from a common soft-breaking phase associated with μ – τ breaking in the neutrino seesaw. Finally, from the soft CP breaking in neutrino seesaw we derive the cosmological CP violation for the baryon asymmetry via leptogenesis. We fully reconstruct the leptogenesis CP-asymmetry from the low energy Dirac CP phase and establish a direct link between the cosmological CP-violation and the low energy Jarlskog invariant. We predict new lower and upper bounds on the θ13 mixing angle, 1°θ136° . In addition, we reveal a new hidden symmetry that dictates the solar mixing angle θ12 by its group-parameter, and includes the conventional tri-bimaximal mixing as a special case, allowing deviations from it.

Realizing dark matter and Higgs inflation in light of LHC diphoton excess

We extend the visible content of the standard model (SM) with a hidden sector composed of three right-handed singlet neutrinos and one singlet Higgs. These extra singlets are charged under a new U(1)X gauge symmetry while the SM particles are not. Two heavy scalar doublets are introduced to play the role of the messengers between the visible and hidden sectors. The neutrinos naturally acquire tiny Dirac masses because the ratio of weak scale over the heavy messenger masses is highly suppressed. Furthermore, the heavy messengers simultaneously generate baryon asymmetry of the universe through their out-of-equilibrium CP-violating decays.

Common origin of soft μ−τ and CP breaking in neutrino seesaw and the origin of matter

Despite the discovery of a Higgs boson h(125 GeV) at the LHC Run-1, its self-interaction has fully evaded direct experimental probe so far. Such self-interaction is vital for electroweak symmetry breaking, vacuum stability, electroweak phase transition, and Higgs ination. It is a most likely place to encode new physics beyond the standard model. We parametrize such new physics by model-independent dimension-6 eective operators, and study their tests via Higgs pair production at hadron colliders. We analyze three major di-Higgs production channels at parton level, and compare the parameter-dependence of total cross sections and kinematic distributions at the LHC (14TeV) and pp(100TeV) hadron collider. We further perform full simulations for the diHiggs production channel gg ! hh ! b b and its backgrounds at the pp (100TeV) hadron collider. We construct four kinds of benchmark points, and study the sensitivities to probing dierent regions of the parameter space of cubic Higgs interactions. We nd that for one-parameter

Neutrino Mass and Baryon Asymmetry from Dirac Seesaw

Abstract Current data from neutrino oscillation experiments are in good agreement with δ = − π 2 and θ 23 = π 4 under the standard parametrization of the mixing matrix. We define the notion of “constrained maximal CP violation” (CMCPV) for predicting these features and study their origin in flavor symmetry. We derive the parametrization-independent solution of CMCPV and give a set of equivalent definitions for it. We further present a theorem on how the CMCPV can be realized. This theorem takes the advantage of residual symmetries in neutrino and charged lepton mass matrices, and states that, up to a few minor exceptions, ( | δ | , θ 23 ) = ( π 2 , π 4 ) is generated when those symmetries are real. The often considered μ – τ reflection symmetry, as well as specific discrete subgroups of O(3), is a special case of our theorem.

Probing new physics of cubic Higgs boson interaction via Higgs pair production at hadron colliders

We study gravitational interaction of Higgs boson through the unique dimension-4 operator xi(HHR)-H-dagger, with H the Higgs doublet and R the Ricci scalar curvature. We analyze the effect of this dimensionless nonminimal coupling xi on weak gauge boson scattering in both Jordan and Einstein frames. We explicitly establish the longitudinal-Goldstone equivalence theorem with nonzero xi coupling in both frames, and analyze the unitarity constraints. We study the xi-induced weak boson scattering cross sections at O(1 30) TeV scales, and propose to probe the Higgs-gravity coupling via weak boson scattering experiments at the LHC (14 TeV) and the next generation pp colliders (50 100 TeV). We further extend our study to Higgs inflation, and quantitatively derive the perturbative unitarity bounds via coupled channel analysis, under large field background at the inflation scale. We analyze the unitarity constraints on the parameter space in both the conventional Higgs inflation and the improved models in light of the recent BICEP2 data.