The experimental status of direct searches for exotic physics beyond the standard model at the Large Hadron Collider

Abstract

The standard model of particle physics is an extremely successful theory of fundamental interactions, but it has many known limitations. It is therefore widely believed to be an effective field theory that describes interactions near the TeV scale. A plethora of strategies exist to extend the standard model, many of which contain predictions of new particles or dynamics that could manifest in proton-proton collisions at the Large Hadron Collider (LHC). As of now, none have been observed, and much of the available phase space for natural solutions to outstanding problems is excluded. If new physics exists, it is therefore either heavy (i.e. above the reach of current searches) or hidden (i.e. currently indistinguishable from standard model backgrounds). We summarize the existing searches, and discuss future directions at the LHC. discrepancy in the anomalous magnetic moment of the muon (g-2) [48], and the strong CP problem [49][50][51]. Even further, there are open questions about long-standing observations, such as whether or not there is an extended Higgs sector [52], why there are multiple generations of fermions with a large mass hierarchy [32,[53][54][55], and why no magnetic monopoles are observed to exist [56]. For these reasons, the SM is considered to be an effective field theory, and that physics beyond the SM (BSM) should exist.There is no shortage of models to explain these elusive phenomenon, with varying degrees of complexity and explanatory power. One very popular group of theories to explain several of these phenomena involve supersymmetric (SUSY) extensions to the SM [12,13]. Many SUSY models contain a particle that only interacts very weakly with ordinary matter (the "lightest SUSY particle", or LSP), providing a simple DM candidate. At the same time, SUSY also attempts to address questions about the hierarchy problem, the nature of space-time, grand unified theories, and even string theory. For this reason, SUSY has long been held as a very attractive BSM physics model, because it can explain a wide range of phenomena with simple assumptions.Unfortunately, as of yet, no easily detectable signals have been observed at the LHC. This, in and of itself, is not necessarily a problem, because the scale of SUSY could always either be heavier than we can currently access, or exists in a region where the signals are hidden among SM backgrounds. The former case, however, limits the ability for SUSY to mitigate the hierarchy problem.The infrared divergences of the mass of the Higgs boson are only canceled if the masses of the SUSY particles are very close to their SM counterparts. This raises questions of whether or not the models themselves "naturally" explain the hierarchy problem. For the case of subtle signatures, of course, such questions of naturalness are less pressing, and can still preserve solutions to the hierarchy problem with a DM candidate.Despite those attractive theoretical features, there is really no a priori reason (other than our personal aesthetic) that one model should address all of ...

SM-GR Reconciliation and Dark Sector

“…under the affine curvature in (29) . This action reveals that the scalar masses (8) cannot give rise to the big hierarchy problem [14] in Table 1 as their Λ 2 ℘ parts eventuate in the non-minimal coupling c φ /4 between the scalars and the curvature scalar [24].…”

“…The action S QFT∪GR is the master formula for all the cosmological, astrophysical and collider phenomena. Its field theory part (the SM plus a BSM sector) and gravity part (the GR plus higher-curvature scalar-tensor theory) are expected to evolve into wider and precise forms as progresses are made in collider experiments [29,30], astrophysical observations [31,22], and cosmological measurements [32,22,33].…”

Fine-Tuned Spin-3/2 and the Hierarchy Problem

“…With the discovery of a resonance at the LHC [1,2] that seems to be rather consistent with the standard model Higgs boson in light of the initial assessment of its properties [3,4]; the electroweak naturalness [5,6] is the foremost problem that we should turn our attention to. Even though many new physics theories have been suggested in order to cure the destabilization of the Higgs mass [7][8][9][10][11][12]; so far no signal of these has been observed [13][14][15]. The lack of any new physics particle at the TeV scale casts doubts on the relevance of the idea of naturalness and strengthens the view that the Standard Model (SM) of electroweak and strong interactions may well be the model of physics at Fermi scale [16][17][18][19].…”

Levels of Composition: from Quarks to HHe+ Molecular Ion

“…Even further, there are open questions about long-standing observations, such as whether or not there is an extended Higgs sector, why there are multiple generations of fermions with a large mass hierarchy, and why no magnetic monopoles are observed to exist. For these reasons, the SM is considered to be an effective field theory, and that physics beyond the SM (BSM) should exist" [1] . For an stimulating and detailed discussion about material things see the book of van Inwagen [2] and the writings collected by Castellani [3] .…”