Higgs Coupling Measurements and the Scale of New Physics.
TL;DR: In this paper, the authors extend previous work on unitarity bounds from the Higgs cubic coupling to Higgs couplings to vector bosons and top quarks, and show that the deviations can be described by the leading higher-dimension gauge invariant operator, as in the SM effective field theory.
Abstract: A primary goal of present and future colliders is measuring the Higgs couplings to Standard Model (SM) particles. Any observed deviation from the SM predictions for these couplings is a sign of new physics whose energy scale can be bounded from above by requiring tree-level unitarity. In this paper, we extend previous work on unitarity bounds from the Higgs cubic coupling to Higgs couplings to vector bosons and top quarks. We find that HL-LHC measurements of these couplings compatible with current experimental bounds may point to a scale that can be explored at the HL-LHC or a next-generation collider. Our approach is completely model-independent: we assume only that there are no light degrees of freedom below the scale of new physics, and allow arbitrary values for the infinitely many couplings beyond the SM as long as they are in agreement with current measurements. We also extend and clarify the methodology of this analysis, and show that if the scale of new physics is above the TeV scale, then the deviations can be described by the leading higher-dimension gauge invariant operator, as in the SM effective field theory.
Citations
More filters
TL;DR: In this paper , it was shown that the scale of new physics could be as low as 10$ TeV, which is well within the reach of the future 100-TeV collider and can also be probed indirectly in the HL-LHC.
6 citations
TL;DR: In this article , effective field theory (EFT) extensions of the Standard Model are used to compute observables (e.g. cross sections with partonic center-of-mass energy) suppressed by a new physics scale M .
Abstract: A bstract Effective Field Theory (EFT) extensions of the Standard Model are tools to compute observables (e.g. cross sections with partonic center-of-mass energy $$ \sqrt{\hat{s}} $$ s ̂ ) as a systematically improvable expansion suppressed by a new physics scale M . If one is interested in EFT predictions in the parameter space where M < $$ \sqrt{\hat{s}} $$ s ̂ , concerns of self-consistency emerge, which can manifest as a violation of perturbative partial-wave unitarity. However, when we search for the effects of an EFT at a hadron collider with center-of-mass energy $$ \sqrt{s} $$ s using an inclusive strategy, we typically do not have access to the event-by-event value of $$ \sqrt{\hat{s}} $$ s ̂ . This motivates the need for a formalism that incorporates parton distribution functions into the perturbative partial-wave unitarity analysis. Developing such a framework and initiating an exploration of its implications is the goal of this work. Our approach opens up a potentially valid region of the EFT parameter space where M ≪ $$ \sqrt{s} $$ s . We provide evidence that there exist valid EFTs in this parameter space. The perturbative unitarity bounds are sensitive to the details of a given search, an effect we investigate by varying kinematic cuts.
4 citations
17 Mar 2022
TL;DR: In this paper , the authors describe how unitarity bounds can con-vert sensitivities for Higgs couplings at future colliders into sensitivities to the scale of new physics.
Abstract: In this Snowmass white paper, we describe how unitarity bounds can con-vert sensitivities for Higgs couplings at future colliders into sensitivities to the scale of new physics. This gives a model-independent consequence of improving these sensitivities and illustrate the impact they would have on constraining new physics. Drawing upon past successful applications of unitarity as a guide for future colliders (e.g. the Higgs mass bound and discover-ing it at the LHC), we hope this data will be useful in the planning for next generation colliders.
3 citations
TL;DR: In this article , it was shown that while the HL-LHC might be able to find new physics in the γγ and γZ sectors, the scale of new physics for both sectors is mostly beyond its reach.
Abstract: A bstract Measuring the Higgs couplings accurately at colliders is one of the best routes for finding physics Beyond the Standard Model (BSM). If the measured couplings deviate from the SM predictions, then this would give rise to energy-growing processes that violate tree-level unitarity at some energy scale, indicating new physics. In this paper, we extend previous work on unitarity bounds from the Higgs potential and the Higgs couplings to vector bosons and the top quark; to the Higgs couplings to γγ and γZ . We find that while the HL-LHC might be able to find new physics in the γZ sector, the scale of new physics in both sectors is mostly beyond its reach. However, accurate measurements of the leading couplings of the two sectors in the HL-LHC can place stringent limits on both the scale of new physics and on other Higgs couplings that are difficult to measure. In addition, the scale of new physics is mostly within the reach of the 100 TeV collider.
2 citations
References
More filters
TL;DR: In this paper, it was shown that the parital wave unitarity is not respected by the tree diagrams for two-body scattering of gauge bosons, and the weak interactions must become strong at high energies.
Abstract: We give an $S$-matrix-theoretic demonstration that if the Higgs-boson mass exceeds ${M}_{c}={(8\ensuremath{\pi}\frac{\sqrt{2}}{3}{G}_{F})}^{\frac{1}{2}}$, parital-wave unitarity is not respected by the tree diagrams for two-body scattering of gauge bosons, and the weak interactions must become strong at high energies. We exhibit the relation of this bound to the structure of the Higgs-Goldstone Lagrangian, and speculate on the consequences of strongly coupled Higgs-Goldstone systems. Prospects for the observation of massive Higgs scalars are noted.
1,206 citations
TL;DR: In this article, a systematic search is made for all renormalizable theories of heavy vector bosons and it is proved that any such theory is tree-unitary if and only if it is equivalent under a point transformation to a spontaneously broken gauge theory, possibly modified by the addition of mass terms for vectors associated with invariant Abelian subgroups.
Abstract: A systematic search is made for all renormalizable theories of heavy vector bosons. It is argued that in any renormalizable Lagrangian theory high-energy unitarity bounds should not be violated in perturbation theory (apart from logarithmic factors in the energy). This leads to the specific requirement of “tree unitarity„; the N -particle S -matrix elements in the tree approximation must grow no more rapidly than E 4- N in the limit of high energy ( E ) at fixed, nonzero angles (i.e., at angles such that all invariants P i − P j i≠j , grow like E 2 ). We have imposed this tree-unitarity criterion on the most general scalar, spinor, and vector Lagrangian with terms of mass dimension less than or equal to four; a certain class of nonpolynomial Lagrangians is also considered. It is proved that any such theory is tree-unitary if and only if it is equivalent under a point transformation to a spontaneously broken gauge theory, possibly modified by the addition of mass terms for vectors associated with invariant Abelian subgroups. Our result suggests that gauge theories are the only renormalizable theories of massive vector particles and that the existence of Lie groups of internal symmetries in particle physics can be traced to the requirement of renormalizability.
743 citations
"Higgs Coupling Measurements and the..." refers methods in this paper
...The calculation of this can be considerably simplified using the equivalence theorem, which tells us that the leading high-energy behavior of scattering amplitudes for longitudinally polarized gauge bosons is given by the amplitude for the corresponding ‘eaten’ NambuGoldstone bosons [4, 21]....
[...]
TL;DR: In this article, the authors study the general signatures of a strongly interacting W, Z system and conclude that these two possibilities can be unambiguously distinguished by a hadron collider facility capable of observing the enhanced production of WW, WZ and ZZ pairs that will occur if W's and Z's have strong interactions.
669 citations
TL;DR: Combined measurements of Higgs boson production cross sections and branching fractions arc are presented in this paper, based on the analyses of the Higgs particle decay modes H -> gamma gamma, ZZ...
Abstract: Combined measurements of Higgs boson production cross sections and branching fractions arc presented. The combination is based on the analyses of the Higgs boson decay modes H -> gamma gamma, ZZ ...
505 citations
TL;DR: In this article, it was shown that if the Higgs boson mass exceeds Mc=(8π23GF)12 partial-wave unitarity is not respected by the tree diagrams for two-body reactions of gauge bosons, then the weak interactions must become strong.
Abstract: It is shown that if the Higgs boson mass exceeds Mc=(8π23GF)12 partial-wave unitarity is not respected by the tree diagrams for two-body reactions of gauge bosons, and the weak interactions must become strong.
493 citations
"Higgs Coupling Measurements and the..." refers background in this paper
...However, what is often not sufficiently emphasized is that if these measurements find a deviation from the SM predictions, then they directly point to a scale of new physics, in exactly the same way that the work of Lee, Quigg, and Thacker pointed to the scale of the Higgs sector before its discovery....
[...]
...Lee, Quigg, and Thacker [8, 9] turned this into a quantitative constraint, showing that tree-level unitarity of longitudinal vector boson scattering could be used to give a bound on the energy scale of the Higgs sector (see also Refs....
[...]
...It is well known that a deviation in the hV V couplings leads to unitarity violation in longitudinal W and Z scattering at high energies [8,9]....
[...]