Baryonic Z' Explanation for the CDF Wjj Excess

The latest CDF anomaly, the excess of dijet events in the invariant-mass window 120-160 GeV in associated production with a $W$ boson, can be explained by a baryonic $Z'$ model in which the $Z'$ boson has negligible couplings to leptons. Although this $Z'$ model is hardly subject to the Drell-Yan constraint from Tevatron, it is constrained by the dijet data from UA2 ($\sqrt{s} = 630$ GeV), and the precision measurements at LEP through the mixing with the SM $Z$ boson. We show that under these constraints this model can still explain the excess in the M_{jj} \sim 120 - 160 GeV window, as well as the claimed cross section $\sigma(W Z') \sim 4$ pb. Implications at the Tevatron would be the associated production of $\gamma Z',\; Z Z'$, and $Z'Z'$ with the $Z' \to jj$. We show that with tightened jet cuts and improved systematic uncertainties both $\gamma Z' \to \gamma jj$ and $Z Z' \to \ell^+ \ell^- j j$ channels could be useful to probe this model at the Tevatron.Comment: 5 pages, 2 figures; Comments added why the current Z jj and gamma jj did not see the excess; matches the published version in PR

Top-phobic heavy Higgs boson as the 750 GeV diphoton resonance

A hint of a new resonance at a mass of 750\,GeV has been observed in the diphoton channel of LHC Run 2 at $\sqrt{s}=13$ TeV. The signal rate is too large to interpret it as a new Higgs boson in the context of weakly-coupled renormalizable models. One way is to reduce its total decay rate, which is possible if the CP-even heavy Higgs boson $H^0$ in the aligned two Higgs doublet model becomes top-phobic. To ensure sufficient gluon fusion production, we introduce vector-like quarks (VLQ). The Higgs precision data as well as the exclusion limits from no excesses in other 8 TeV LHC searches of $Z\gamma$, $b\bar{b}$, $\tau^+\tau^-$, and $jj$ channels are simultaneously included. In Type I, top-phobic $H^0$ cannot explain the 750\,GeV diphoton signal and the Higgs precision data simultaneously since the universal Yukawa couplings of the up-type and down-type VLQs always make more contribution to $h^0$ than to $H^0$. In Type II, small Yukawa coupling of the up-type VLQ but sizable Yukawa coupling for the down-type VLQ is shown to explain the signal while satisfying other LHC exclusion limits.Comment: Errors in the Type I calculation are corrected, and references are adde

The B ---> {\pi} K puzzle and the Bulk Randall-Sundurm model

The recent measurements of the direct CP asymmetries ($A_{CP}$) in the penguin-dominated $B\to K \pi$ decays show some discrepancy from the standard model (SM) prediction. While $A_{CP}$ of $B^+ \to \pi^0 K^+$ and that of $B^0 \to \pi^- K^+$ in the naive estimate of the SM are expected to have very similar values, their experimental data are of the opposite sign and different magnitudes. We study the effects of the custodial bulk Randall-Sundrum model on this $A_{CP}$. In this model, the misalignment of the five-dimensional (5D) Yukawa interactions to the 5D bulk gauge interactions in flavor space leads to tree-level flavor-changing neutral current by the Kaluza-Klein gauge bosons. In a large portion of the parameter space of this model, the observed nonzero $A_{CP}(B^+ \to \pi^0 K^+) - A_{CP}(B^0 \to \pi^- K^+)$ can be explained only with low Kaluza-Klein mass scale $M_{KK}$ around 1 TeV. Rather extreme parameters is required to explain it with M_{KK}\simeq 3\tev. The new contributions to well-measured branching ratios of $B \to K \pi$ decays are also shown to be suppressed.Comment: 18 pages, 2 figure

How Resonance-Continuum Interference Changes 750 GeV Diphoton Excess: Signal Enhancement and Peak Shift

The new scalar resonance contribution to the 750 GeV diphoton excess observed at the LHC 13 TeV necessarily interferes with the continuum background in the $gg\to \gamma \gamma$. The interference has two considerable effects: (1) enhancing or suppressing diphoton signal rate due to the imaginary-part interference and (2) distorting resonance shape due to the real-part interference. From the best-fit study of two benchmark models (two Higgs doublets with $\sim$50 GeV widths and a singlet scalar with 5 GeV width, both extended with vector-like fermions), we find that the resonance contribution to the 750 GeV excess can be enhanced by a factor of 2(1.6) for 3(6) fb signal rate and the 68%(95%) CL best-fit mass range can shift by 1-4 (any ${\cal O}$(1)) GeV. If the best-fit excess rate decreases with future data, the interference effects will become more significant. The inevitable interferences can also provide a consistency check of a resonance hypothesis, whether or not future precision shape measurements confirm a Breit-Wigner shape or discover interesting deviations.Comment: 23 pages, 14 figure

A probe of the Radion-Higgs mixing in the Randall-Sundrum model at e^+ e^- colliders

In the Randall-Sundrum model, the radion-Higgs mixing is weakly suppressed by the effective electroweak scale. A novel feature of the existence of gravity-scalar mixing would be a sizable three-point vertex among the KK graviton, Higgs and radion. We study this vertex in the process e^+ e^- -> h phi, which is allowed only with a non-zero radion-Higgs mixing. It is shown that the angular distribution is a unique characteristic of the exchange of massive spin-2 gravitons, and the total cross section at the future e^+ e^- collider is big enough to cover a large portion of the parameter space where the LEP/LEP II data cannot constrain.Comment: 14pages, RevTeX, 5 figure

Dip or nothingness of a Higgs resonance from the interference with a complex phase

We show that new resonance shapes -- a pure dip, nothingness and an enhanced pure peak -- can be produced from the interference between resonance and continuum with a relative phase. Production conditions of those new shapes are derived based on a general parameterization of the interference. The narrow width approximation is modified to work with the non-zero imaginary part of interference, and the correction factor can characterize the resonance shape. We demonstrate that the new resonance shapes of heavy Higgs bosons, $H^0$ and $A^0$ in the Type II aligned two Higgs doublet model, generally show up in $gg \to H^0/A^0 \to t\bar{t}$ as well as $b\bar{b}$ and $\gamma \gamma$ channels. The pure $A^0$ resonance dip in the $t\bar{t}$ channel is a particularly interesting signal as it can be probed well by the current search techniques that do not even take into account interferences; the high-luminosity LHC 14 TeV can perhaps probe a large part of its parameter space.Comment: 10 pages, 7 figure