Search

We provide a possible interpretation of excesses reported by ATLAS and CMS at around 95GeV, 650GeV and possibly 320GeV, in terms of CP-even scalars. In particular, the combined {\sl global} statistical significances of independent indications for a 650GeV object reach the $4\sigma$ level! While this seems sufficient incentive for a further investigation, this object cannot be fitted in tradional singlet or doublet extensions of the Standard Model. It requires by itself a larger extension with doubly-charged scalars, that naturally fits the two other excesses on top of the SM-like 125~GeV Higgs. We describe the minimal model and give some numerical illustrations., Comment: To appear in the proceedings of the 29th International Symposium on Particles, Strings and Cosmology (PASCOS 2024) in Quy Nhon, Vietnam, 7-13 July, 2024

There have been indications of several new resonances at the Large Hadron Collider (LHC). Two of them, at about 95 GeV and 650 GeV, have been indicated by more than one experiments and have reached statistical significance worthy of a serious investigation. Conservatively using only the numbers given by the experimental collaborations, we find combined global significances around 3$\sigma$ and 4$\sigma$ respectively for the 95 GeV and 650 GeV putative resonances. There are some more which may soon become very significant. We show that the data on only the 650 GeV resonance, assuming they stand the test of time, predict the existence of a doubly-charged scalar, and make the extensions of the scalar sector like those by gauge singlet scalars, the 2-Higgs doublet models or the Georgi-Machacek model, highly disfavored. We provide the readers with a minimalistic model that can explain all the indications. Such a model can also accommodate the hints of a singly charged scalar at about 375 GeV, and a doubly charged scalar at about 450 GeV, as found by both the major LHC Collaborations, the combined global significance for each of them being above $2.5\sigma$. Our analysis comes with the obvious caveat that the allowed parameter space that we find depends on the available data on all the new resonances, and may change in future., Comment: 24 pages, 14 figure files, uses Revtex

Minimal triplet scalar extension of the Standard Model demanding custodial symmetry gives rise to the extended Georgi-Machacek (eGM) model. We compute one-loop corrections to all $2 \rightarrow 2$ bosonic scattering amplitudes in the eGM model, and place next-to-leading order (NLO) unitarity bounds on the quartic couplings. Additionally, we derive state-of-the-art constraints on the quartic couplings demanding the stability of the scalar potential. We perform a global fit of the eGM model to these theoretical bounds and to the latest Higgs signal strength results from the LHC detectors. In addition to the custodial symmetry, imposing a global $SU(2)_L\otimes SU(2)_R$ symmetry on the scalar potential at the electroweak scale results in the well-known Georgi-Machacek (GM) model. We assess the impact of the state-of-the-art theoretical constraints on the fit to the Higgs signal strength data in the GM model, with particular emphasis on the NLO unitarity bounds. We observe that the global fit disfavors the region where $\kappa_V$ is greater than $1.05$ with a 95.4\% confidence level. We obtain an upper limit on the absolute values of the quartic couplings to be 1.9 (4.2) and see that the absolute mass differences between the heavy Higgs bosons cannot exceed 400 GeV (380 GeV) in the GM (eGM) model. Finally, we find that the maximal mass splitting within the members of custodial symmetric multiplets is restricted to be smaller than 210 GeV in the eGM model., Comment: 58 pages, 13 figures. Comments are welcome

In this paper, we revisit the experimental constraints on the multipolar dark matter that has derivative coupling to the visible sector mediated by the Standard Model photon. The momentum dependent interaction enables them to be captured efficiently within massive celestial bodies boosted by their steep gravitational potential. This phenomena makes compact celestial bodies as an efficient target to probe such type of dark matter candidates. We demonstrate that a synergy of the updated direct detection results from DarkSide-50 and LUX-ZEPLIN together with IceCube bounds on high energy solar neutrinos from dark matter capture disfavour the viable parameter space of the dipolar dark matter scenario. Whereas, for the anapole dark matter scenario, a narrow window survives that lies within the reach of prospective heating signals due to the capture of dark matter at cold neutron stars., Comment: 12 pages, 5 figures; new appendix added

In view of the future Higgs factories, this work presents the status of scalar searches at the LHC with an emphasis on the H(650) resonance which has been observed in WW, ZZ and h(95)h(125) channels, with a cumulative evidence of about 7 s.d. global significance. Its interpretation in models, restricted to extension of the scalar sector by SU(2) singlets and doublets, is clearly excluded, while its interpretation in models with additional triplets requires an extension with respect to the conventional Georgi-Machacek model. A general picture of these searches is updated, showing that h(95) is also reaching a similar level of evidence while two other candidates, A(400) and h(151), although less prominent, are above the 4 s.d. global evidence., Comment: 14 pages, 9 figures, Work presented by F. Richard at the ECFA workshop on Higgs/EW/top factories in DESY, October 2022

The recent CDF-II measurement of the mass of the $W$ boson shows a significant tension with the Standard Model (SM) expectation, even when averaged with earlier measurements. The tension can be explained in the framework of any beyond-SM dynamics that contributes substantially to the oblique $S$ and $T$ parameters. As a typical example of such beyond-SM physics, we try to explain the tension in the framework of the Georgi-Machacek model that keeps $\rho=1$ at the tree-level, and explore the parameter space that can accommodate the $W$ mass shift. We find that a sizeable split between the custodial triplet and 5-plet of scalars can help alleviate the tension to a large extent, and raise the $W$-mass by about 30 MeV over its SM value., Comment: 8 pages, 2 figures

In an SU(2) gauge theory, if the gauge bosons turn out to be degenerate after spontaneous symmetry breaking, obviously these mass terms are invariant under a global SU(2) symmetry that is unbroken. The pure gauge terms are also invariant under this symmetry. This symmetry is called the {\em custodial symmetry} (CS). In $\rm SU(2)\times U(1)$ gauge theories, CS implies a mass relation between the $W$ and the $Z$ bosons. The Standard Model (SM), as well as various extensions of it in the scalar sector, possess such a symmetry. In this paper, we critically examine the notion of CS and show that there may be three different classes of CS, depending on the gauge couplings and self-couplings of the scalars. Among old models that preserve CS, we discuss the Two-Higgs Doublet Model and the one doublet plus two triplet model by Georgi and Machacek. We show that for two-triplet extensions, the Georgi-Machacek model is not the most general possibility with CS. Rather, we find, as the most general extension, a new model with more parameters and hence a richer phenomenology. Some of the consequences of this new model have also been discussed., Comment: 29 pages, 5 figures. Major changes in Section 2 regarding the classification of custodial symmetry. Version accepted in Physical Review D

Without any mechanism to protect its mass, the self-energy of the Higgs boson diverges quadratically, leading to the hierarchy or fine-tuning problem. One bottom-up solution is to postulate some yet-to-be-discovered symmetry which forces the sum of the quadratic divergences to be zero, or almost negligible; this is known as the Veltman condition. Even if one assumes the existence of some new physics at a high scale, the fine-tuning problem is not eradicated, although it is softer than what it would have been with a Planck scale momentum cut-off. We study such divergences in an effective theory framework, and construct the Veltman condition with dimension-six operators. We show that there are two classes of diagrams, the one-loop and the two-loop ones, that contribute to quadratic divergences, but the contribution of the latter is suppressed by a loop factor of $1/16\pi^2$. There are only six dimension-six operators that contribute to the one-loop category, and the Wilson coefficients of these operators play an important role towards softening the fine-tuning problem. We find the parameter space for the Wilson coefficients that satisfies the extended Veltman condition, and also discuss why one need not bother about the $d>6$ operators. The parameter space is consistent with the theoretical and experimental bounds of the Wilson coefficients, and should act as a guide to the model builders., Comment: 10 pages, 2 figures. v2: Corrected an error, added an Appendix. Version to be published in Physical Review D

Recently, the CMS Collaboration observed the hint of a resonance decaying to two photons at about 96 GeV with a local significance of $2.8\sigma$. While it is too early to say whether this will stand the test of time, such a resonance can easily be accommodated in many extensions of the Standard Model (SM). The more challenging part is to tune such an extension so that the required number of diphoton events is reproduced. Assuming that the new resonance is a scalar, we propose that the signal may come either from an ultraviolet complete model with vectorial quarks, or a model involving gluon-scalar and photon-scalar effective operators. We then incorporate this portal to several extensions of the SM that include one or more cold dark matter candidates, and try to investigate how the existence of such a scalar resonance affects the parameter space of such models. As expected, we find that with such a scalar, the parameter space gets more constrained and hence, more tractable. We show how significant constraints can be placed on the parameter space, not only from direct dark matter searches or LHC data but also from theoretical considerations like scattering unitarity or stability of the potential, and discuss some novel features of the allowed parameter space., Comment: 23 pages, 25 figures. v2: significant changes, with a proper treatment of the diphoton signal. Version to be published in Nuclear Physics B