Showing papers by "Ian Low published in 2020"
TL;DR: In this article, a cubic bifundamental/biadjoint scalar theory for SO(N + 1 )/SO(N) nlσm was proposed.
35 citations
TL;DR: In this paper, the authors enumerate the independent operators without external sources in ChPT using an on-shell method, by counting and presenting the soft blocks at each order in the derivative expansion, up to the massless onshell condition and total momentum conservation.
Abstract: Chiral perturbation theory (ChPT) is a low-energy effective field theory of QCD and also a nonlinear sigma model based on the symmetry breaking pattern $\mathrm{SU}({N}_{f})\ifmmode\times\else\texttimes\fi{}\mathrm{SU}({N}_{f})\ensuremath{\rightarrow}\mathrm{SU}({N}_{f})$. In the limit of massless ${N}_{f}$ quarks, we enumerate the independent operators without external sources in ChPT using an on-shell method, by counting and presenting the soft blocks at each order in the derivative expansion, up to $\mathcal{O}({p}^{10})$. Given the massless on-shell condition and total momentum conservation, soft blocks are homogeneous polynomials of kinematic invariants exhibiting Adler's zero when any external momentum becomes soft and vanishing. In addition, soft blocks are seeds for recursively generating all tree amplitudes of Nambu-Goldstone bosons without recourse to ChPT, and in one-to-one correspondence with the ``low-energy constants'' which are the Wilson coefficients. Relations among operators, such as those arising from equations of motion, integration by parts, Hermiticity, and symmetry structure, manifest themselves in the soft blocks in simple ways. We find agreements with the existing results up to next-to-next-to-next-to-leading order (NNNLO) and make a prediction at ${\mathrm{N}}^{4}\mathrm{LO}$.
18 citations
TL;DR: In this article, a fit to the Wilson coefficients of the nonlinear Lagrangian was performed using the golden H 4L decay channel, where the shape information in the fully differential spectra was used to identify regions of parameter space where current LHC constraint on f is still weak.
Abstract: The most salient generic feature of a composite Higgs boson resides in the nonlinearity of its dynamics, which arises from degenerate vacua associated with the pseudo-Nambu–Goldstone (PNGB) nature of the Higgs boson. It has been shown that the nonlinear Higgs dynamics is universal in the IR and controlled only by a single parameter f, the decay constant of the PNGB Higgs. In this work we perform a fit, for the first time, to Wilson coefficients of $${\mathcal {O}}(p^4)$$
operators in the nonlinear Lagrangian using the golden H $$\rightarrow $$
4L decay channel. By utilizing both the “rate” information in the signal strength and the “shape” information in the fully differential spectra, we provide limits on the Goldstone decay constant f, as well as $${\mathcal {O}}(p^4)$$
Wilson coefficients, using Run 2 data at the LHC. In rate measurements alone, the golden channel prefers a negative $$\xi =v^2/f^2$$
corresponding to a non-compact coset structure. Including the shape information, we identify regions of parameter space where current LHC constraint on f is still weak, allowing for $$\xi \lesssim 0.5$$
or $$\xi \gtrsim -0.5$$
. We also comment on future sensitivity at the high-luminosity upgrade of the LHC which could allow for simultaneous fits to multiple Wilson coefficients.
5 citations
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TL;DR: In this article, the authors propose novel CP-violating observables in complex two-Higgs-doublet models and undertake a systematic study of the interplay between Higgs alignment and CPviolation.
Abstract: We propose novel CP-violating observables in complex two-Higgs-doublet models and undertake a systematic study of the interplay between Higgs alignment and CP-violation, which enables us to distinguish two separate sources of CP-violation in the scalar sector: in the mixing and in the decay, and identify a scenario where departures from Higgs alignment could be present independently of CP-violation. After including constraints from the electric dipole moment and measurements at the Large Hadron Collider, we suggest a smoking-gun signal of CP-violation, without recourse to the typically required angular correlations, in the Higgs-to-Higgs decay, $(h_3\to h_2 h_1)$, where $h_3, h_2$, and $h_1$ are the heaviest, second heaviest and the SM-like neutral Higgs bosons, respectively. The mere presence of this decay channel, which is non-zero only away from the alignment limit, is sufficient to establish CP-violation in a complex two-Higgs-doublet model. A distinct discovery channel lies in final states with three 125 GeV Higgs bosons, which has yet to be searched for, and could be detected at the high-luminosity LHC.
3 citations
TL;DR: In this paper, a light photon was introduced to the minimal Higgs portal model, by coupling the Higgs boson to ''dark QED'' containing fermionic dark matter, which gives rise to rich and interesting collider phenomenology.
Abstract: We introduce a light dark photon ${A}_{\ensuremath{\mu}}^{\ensuremath{'}}$ to the minimal Higgs portal model, by coupling the Higgs boson to ``dark QED'' containing fermionic dark matter, which gives rise to rich and interesting collider phenomenology. There are two prominent features in such a simple extension---the Higgs boson could have decays into the long-lived dark photon through the ``mono-${A}^{\ensuremath{'}}$ channel,'' or into multiple collimated leptons via ``darkonium,'' depending on the mixing parameter of the ${A}_{\ensuremath{\mu}}^{\ensuremath{'}}$ with the visible photon. We initiate a study on the possibility of probing the parameter space of the model in both the energy and the lifetime frontiers at the Large Hadron Collider.
3 citations