LHC Constraints Research Articles

Broad toplike vector quarks at LHC and HL-LHC

Toplike vector quarks arising from underlying strong sectors are expected to have large decay widths pushing them beyond the narrow width approximation. In this paper we consider a broad colored vector quark that strongly couples to an exotic pseudoscalar. We use the full 1PI resummed propagator for the exotic quark to recast the present LHC constraints ruling out masses below $\ensuremath{\sim}1.2(1.1)\text{ }\text{ }\mathrm{TeV}$ for width to mass ratio of 0.1(0.6). We utilize machine learning techniques that are demonstratively more efficient than traditional cut based searches to present the reach of HL-LHC on the parameter space of this broad resonance. We find that at $3\text{ }\text{ }{\mathrm{ab}}^{\ensuremath{-}1}$ the HL-LHC has a discovery potential up to 1.6 TeV dominated by the pair production channel. We study the feasibility of using machine learning techniques to analyze the broad resonance peaks expected from these exotic quarks at collider experiments like the LHC.

Vector boson dark matter from trinification

We show how trinification models based on the gauge group SU(3)C× SU(3)L× SU(3)R realized near the TeV scale can provide naturally a variety of dark matter (DM) candidates. These models contain a discrete T parity which may remain unbroken even after spontaneous symmetry breaking. The lightest T-odd particle, which could be a fermion, a scalar, or a gauge boson, can constitute the dark matter of the universe. This framework naturally admits a doublet-singlet fermionic DM, a singlet scalar DM, or a vector boson DM. Here we develop the vector boson DM scenario wherein the DM couples off-diagonally with the usual fermions and vector-like fermions present in the theory. We show consistency of this framework with dark matter relic abundance and direct detection limits as well as LHC constraints. We derive upper limits of 900 GeV on the vector gauge boson DM mass and 4.5 TeV on the vector-like quark masses. We also show the consistency of spontaneous gauge symmetry breaking down to Standard Model times an extra U(1) while preserving the T-parity.

Gluino-SUGRA scenarios in light of FNAL muon g \u2013 2 anomaly

Gluino-SUGRA ( overset{sim }{g} SUGRA), which is an economical extension of the predictive mSUGRA, adopts much heavier gluino mass parameter than other gauginos mass parameters and universal scalar mass parameter at the unification scale. It can elegantly reconcile the experimental results on the Higgs boson mass, the muon g − 2, the null results in search for supersymmetry at the LHC and the results from B-physics. In this work, we propose several new ways to generate large gaugino hierarchy (i.e. M3 » M1, M2) for overset{sim }{g} SUGRA model building and then discuss in detail the implications of the new muon g − 2 results with the updated LHC constraints on such overset{sim }{g} SUGRA scenarios. We obtain the following observations: (i) for the most interesting M1 = M2 case at the GUT scale with a viable bino-like dark matter, the overset{sim }{g} SUGRA can explain the muon g − 2 anomaly at 1σ level and be consistent with the updated LHC constraints for 6 ≤ M3/M1 ≤ 9 at the GUT scale; (ii) For M1 : M2 = 5 : 1 at the GUT scale with wino-like dark matter, the overset{sim }{g} SUGRA model can explain the muon g − 2 anomaly at 2σ level and be consistent with the updated LHC constraints for 3 ≤ M3/M1 ≤ 3.2 at the GUT scale; (iii) For M1 : M2 = 3 : 2 at the GUT scale with mixed bino-wino dark matter, the overset{sim }{g} SUGRA model can explain the muon g − 2 anomaly at 1σ level and be consistent with the updated LHC constraints for 6.9 ≤ M3/M1 ≤ 7.5 at the GUT scale. Although the choice of heavy gluino will always increase the FT involved, some of the 1σ/2σ survived points of Delta {a}_{mu}^{mathrm{combine}} can still allow low EWFT of order several hundreds and be fairly natural. Constraints from (dimension-five operator induced) proton decay are also discussed.

Collider prospects for the muon g−2 in a general two-Higgs-doublet model

Recent progress on muon $g-2$ measurement prompts one to take it even more seriously. In the general two Higgs doublet model that allows extra Yukawa couplings, we take a simplified approach of single enhanced coupling. We fix the charged lepton flavor violating coupling, $\rho_{\tau\mu} = \rho_{\mu\tau}$, via the one-loop mechanism, for illustrative masses of the heavy scalar $H$ and pseudoscalar $A$, where we assume $m_A = m_{H^+}$. Since extra top Yukawa couplings are plausibly the largest, we turn on $\rho_{tt}$ and find that LHC search for $gg \to H,\,A \to \tau\mu$ gives more stringent bound than from $\tau\to \mu\gamma$ with two-loop mechanism. Turning on a second extra top Yukawa coupling, $\rho_{tc}$, can loosen the bound on $\rho_{tt}$, but LHC constraints can again be more stringent than from $B \to D\mu\nu$ vs $De\nu$ universality. This means that evidence for $H,\,A \to \tau\mu$ may yet emerge with full LHC Run 2 data, while direct search for $\tau^\pm\mu^\mp bW^+$ or $t\bar cbW^+$ (plus conjugate) may also bear fruit.

Leptophilic U(1) massive vector bosons from large extra dimensions

We demonstrate that the discrepancy between the anomalous magnetic moment measured at BNL and Fermilab and the Standard Model prediction could be explained within the context of low-scale gravity and large extra-dimensions. The dominant contribution to (g−2)μ originates in Kaluza-Klein (KK) excitations (of the lepton gauge boson) which do not mix with quarks (to lowest order) and therefore can be quite light avoiding LHC constraints. We show that the KK contribution to (g−2)μ is universal with the string scale entering as an effective cutoff. The KK tower provides a unequivocal distinctive signal which will be within reach of the future muon smasher.

Supersymmetric interpretation of the muon g \u2013 2 anomaly

The Fermilab Muon g− 2 collaboration recently announced the first result of measurement of the muon anomalous magnetic moment (g− 2), which confirmed the previous result at the Brookhaven National Laboratory and thus the discrepancy with its Standard Model prediction. We revisit low-scale supersymmetric models that are naturally capable to solve the muon g− 2 anomaly, focusing on two distinct scenarios: chargino-contribution dominated and pure-bino-contribution dominated scenarios. It is shown that the slepton pair-production searches have excluded broad parameter spaces for both two scenarios, but they are not closed yet. For the chargino-dominated scenario, the models with {m}_{{tilde{mu}}_{mathrm{L}}}gtrsim {m}_{{tilde{chi}}_1^{pm }} are still widely allowed. For the bino-dominated scenario, we find that, although slightly non-trivial, the region with low tan β with heavy higgsinos is preferred. In the case of universal slepton masses, the low mass regions with {m}_{tilde{mu}} ≲ 230 GeV can explain the g− 2 anomaly while satisfying the LHC constraints. Furthermore, we checked that the stau-bino coannihilation works properly to realize the bino thermal relic dark matter. We also investigate heavy staus case for the bino-dominated scenario, where the parameter region that can explain the muon g− 2 anomaly is stretched to {m}_{tilde{mu}} ≲ 1.3 TeV.

Muon g \u2212 2 in gauge mediation without SUSY CP problem

We discuss gauge mediated supersymmetry breaking models which explain the observed muon anomalous magnetic moment and the Higgs boson mass simultaneously. The successful explanation requires the messenger sector which violates the relation motivated by the grand unification theory (GUT). The naive violation of the GUT relation, however, ends up with the CP problem. We propose a model in which the phases of the gaugino masses are aligned despite the violation of the GUT relation. We also consider a model which generates the μ-term and the additional Higgs soft masses squared without causing CP violation. As a result, we find a successful model which explains the muon anomalous magnetic moment and the Higgs boson mass. The model is also free from the CP, flavor-changing neutral current and the lepton flavor violation problems caused by the subdominant gravity mediation effects. The lightest supersymmetric particles are gravitino/goldstini and the next-to-lightest ones are the Wino/Higgsinos in the typical parameter space. We also study the LHC constraints.

Fermionic decays of NMSSM Higgs bosons under LHC 13 TeV constraints

This paper investigates the impact of the recent LHC constraints on the Higgs sector in the semi-constrained version of the Next-to-Minimal Supersymmetric Standard Model. Our analysis focuses on the parameter space for which the value of the Higgs doublet-singlet coupling, λ, is large as possible, while the ratio between the vacuum expectation values of the two Higgs doublets, tanβ, is small as possible. Under the current constraints, we present the possible fermionic decay channels and reduced cross-section into fermions final states for the lightest neutral Higgs bosons in the NMSSM, (h1,h2, and a1). We found that the branching ratios of the non SM-like Higgs (a1 and h2) into a pair of bottom quarks are near 90% level when the Higgs mass below 400 GeV. Moreover, the branching ratio of h2/a1→tt¯ can reach unity for all mass ranges when these bosons are mostly singlet.

Testing leptoquark/EFT in {bar{B}} rightarrow {D^{(*)}}l{bar{nu }} at the LHC

We investigate the current LHC bounds on New Physics (NP) that contributes to {bar{B}} rightarrow {D^{(*)}}l{bar{nu }} for l = (e,mu ,tau ) by considering both leptoquark (LQ) models and an effective-field-theory (EFT) Hamiltonian. Experimental analyses from l+text {missing} searches with high p_T are applied to evaluate the NP constraints with respect to the Wilson coefficients. A novel point of this work is to show difference between LQs and EFT for the applicable LHC bound. In particular, we find that the EFT description is not valid to search for LQs with the mass less than lesssim 10,text {TeV} at the LHC and leads to overestimated bounds. We also discuss future prospects of high luminosity LHC searches including the charge asymmetry of background and signal events. Finally, a combined summary for the flavor and LHC bounds is given, and then we see that in several NP scenarios the LHC constraints are comparable with the flavor ones.

Artificial proto-modelling: building precursors of a next standard model from simplified model results

We present a novel algorithm to identify potential dispersed signals of new physics in the slew of published LHC results. It employs a random walk algorithm to introduce sets of new particles, dubbed “proto-models”, which are tested against simplified-model results from ATLAS and CMS (exploiting the SModelS software framework). A combinatorial algorithm identifies the set of analyses and/or signal regions that maximally violates the SM hypothesis, while remaining compatible with the entirety of LHC constraints in our database. Demonstrating our method by running over the experimental results in the SModelS database, we find as currently best-performing proto-model a top partner, a light-flavor quark partner, and a lightest neutral new particle with masses of the order of 1.2 TeV, 700 GeV and 160 GeV, respectively. The corresponding global p-value for the SM hypothesis is pglobal≈ 0.19; by construction no look-elsewhere effect applies.

Single-top final states as a probe of top-flavoured dark matter models at the LHC

Models incorporating flavoured dark matter provide an elegant solution to the dark matter problem, evading the tight LHC and direct direction constraints on simple WIMP models. In Dark Minimal Flavour Violation, a simple framework of flavoured dark matter with new sources of flavour violation, the constraints from thermal freeze-out, direct detection experiments, and flavour physics create well-defined benchmark scenarios for these models. We study the LHC phenomenology of four such scenarios, focusing on final states where a single top quark is produced accompanied by no jets, one jet from the fragmentation of light quarks or a b-tagged jet. For each of these signatures we develop a realistic LHC analysis, and we show that the proposed analyses would increase the parameter space coverage for the four benchmarks, compared to existing flavour-conserving LHC analyses. Finally we show the projected discovery potential of the considered signatures for the full LHC statistics at 14 TeV, and for the High Luminosity LHC.

Lepton flavor violations in SUSY models for muon g \u2212 2 with right-handed neutrinos

We consider supersymmetric (SUSY) models for the muon g − 2 anomaly without flavor violating masses at the tree-level. The models can avoid LHC constraints and the vacuum stability constraint in the stau-Higgs potential. Although large flavor violating processes are not induced within the framework of minimal SUSY standard model, once we adopt a seesaw model, sizable lepton flavor violating (LFV) processes such as μ → eγ and μ → e conversion are induced. These LFV processes will be observed at future experiments such as MEG-II, COMET and Mu2e if right-handed neutrinos are heavier than 109 GeV motivated by the successful leptogenesis. This conclusion is somewhat model independent since Higgs doublets are required to have large soft SUSY breaking masses, leading to flavor violations in a slepton sector via neutrino Yukawa interactions.

Fat brane and seesaw mechanism in extra dimensions

In this paper we present a higher-dimensional seesaw mechanism. We consider a single, flat extra dimension, where a fat brane is localized and contains the standard model (SM) fields, similar to Universal Extra Dimension models. There is only one Dirac fermion in the bulk, and in four dimensions it results in two towers of Kaluza-Klein (KK) Majorana sterile neutrinos, whose mass mixing with the SM neutrinos is suppressed due to a brane-localized kinetic term. The interaction between the sterile neutrinos and the SM is through the usual coupling with the Higgs boson, where the coupling depends upon the compactification radius $R^{-1}=10^{-2}-1$ GeV and the width of the fat brane $L^{-1}=2$ TeV, where the latter value is chosen to avoid LHC constraints. Due to this suppression mechanism the mass of the lightest sterile neutrinos can be of order $\mathcal{O}(1-10)$~\text{TeV} while naturally explaining the small SM neutrino mass, which in turn is easily obtained for a large range of parameter choices. Furthermore, neutrino oscillations are not substantially influenced by the tower of sterile KK particles. Finally, leptogenesis is investigated in this setup, and it is viable for some values within the parameter space.

LHC constraints on W^prime ,~Z^prime that couple mainly to third generation fermions

We use the results of CMS and ATLAS searches for resonances that decay to tau nu or tb and tau ^+tau ^- or t{bar{t}} final states to constrain the parameters of non-universal W^prime and Z^prime gauge bosons that couple preferentially to the third generation. For the former we consider production from cbar{b} annihilation and find very weak constraints on the strength of the interaction and only for the mass range between 800 and 1100 GeV from the pp rightarrow tau _h p_T^{mathrm{miss}} channel. The constraints on the latter are much stronger and arise from both t{bar{t}} and tau ^+tau ^- production. Treated separately, we find that the weak constraints on the W^prime still permit an explanation of the R(D^{(star )}) anomalies with a light sterile neutrino whereas the stronger constraints on the Z^prime exclude significant light sterile neutrino contributions to the K rightarrow pi nu bar{nu } rates. Within specific models the masses of W^prime and Z^prime are of course related and we briefly discuss the consequences.

A golden probe of nonlinear Higgs dynamics

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.

Testing Yukawa unification at LHC Run-3 and HL-LHC

We explore t-b-τ Yukawa unification (YU) in a supersymmetric SU(4)c× SU(2)L× SU(2)R model without imposing a discrete left-right (L-R) symmetry. A number of interesting solutions that are compatible with t-b-τ YU, LSP neutralino dark matter (DM), and LHC and other experimental constraints are identified. In particular, they include gluino-neutralino and stau-neutralino coannihilation scenarios, where the NLSP gluino mass can range from 1–3 TeV. Higgsino-like dark matter solutions are also identified for which gluino masses can approach 5 TeV or so. This scenario will be tested at LHC Run-3 and its future upgrades.

Lepton flavor violation and dilepton tails at the LHC

Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes pp rightarrow ell _k ell _l (with kne l). The current (projected) limits derived in this paper from LHC data with 36~mathrm {fb}^{-1} (3~mathrm {ab}^{-1}) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic brightarrow d transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays Krightarrow pi ell ^{pm }_k ell ^{{mp }}_l, Brightarrow pi ell ^{pm }_k ell ^{{mp }}_l and Brightarrow K^{(*)} ell ^{pm }_k ell ^{{mp }}_l.

Minimal Z′ models for flavor anomalies

By allowing gauge anomaly cancellation between fermions in different families we find a non-universal solution for a Z′ family of models with the same content of fermions of the standard model plus three right-handed neutrinos. We also impose constraints from the Yukawa interaction terms in such a way that at the end we obtain a solution with six free parameters. Our solution contains as particular cases well-known models in the literature. As an application, we report a model that evades LHC constraints, flavor changing neutral currents and low energy constraints. Simultaneously, the model is able to explain the flavor anomalies in the Wilson coefficients C9(μ) and C10(μ) without modifying the corresponding Wilson coefficients for the first family. In our approach, this procedure is always possible for Z′ masses smaller than ∼2.5 TeV.

Any room left for technicolor? Holographic studies of NJL assisted technicolor

We use a holographic description of technicolor dynamics to study gauge theories that only break chiral symmetry when aided by a strong four fermion interaction. These Nambu-Jona-Lasinio (NJL) assisted technicolor models provide examples of different dynamics from walking technicolor which can, by tuning, generate a light higgs like $\sigma$ meson. We compute the vector meson ($\rho$) and axial vector meson (A) spectrum for a variety of models with techni-quarks in the fundamental representation, enlarging the available parameter space over a previous analysis of walking theories. These predictions determine the parameter space of a low energy effective description where LHC constraints from dilepton channels have already been applied. Many of the models with low numbers of electroweak doublets still lie beyond current constraints and motivate exploration of new signatures beyond dilepton for LHC and a 100 TeV proton collider.

Confronting the neutralino and chargino sector of the NMSSM with the multilepton searches at the LHC

We test the impact of the ATLAS and CMS multi-lepton searches performed at the LHC with 8 as well as 13 TeV center-of-mass energy (using only the pre-2018 results) on the chargino and neutralino sector of the NMSSM. Our purpose consists in analyzing the actual reach of these searches for a full model and in emphasizing effects beyond the MSSM that affect the performance of current (MSSM-inspired) electroweakino searches. To this end, we consider several scenarios characterizing specific features of the NMSSM electroweakino sector. We then perform a detailed collider study, generating Monte-Carlo events through Pythia and testing against current LHC constraints implemented in the public tool CheckMATE. We find e.g. that SUSY decay chains involving intermediate singlino or Higgs-singlet states can modify the naive MSSM-like picture of the constraints by inducing final-states with softer or less-easily identifiable SM particles -- reversely, a compressed configuration with singlino NLSP occasionally induces final states that are rich with photons, which could provide complementary search channels.