A leptophobic Z ′ that does not couple with the Standard Model leptons can evade the stringent bo... more A leptophobic Z ′ that does not couple with the Standard Model leptons can evade the stringent bounds from the dilepton-resonance searches. In our earlier paper [T. Arun et al., Search for the Z ′ boson decaying to a right-handed neutrino pair in leptophobic U(1) models, Phys. Rev. D, 106 (2022) 095035; arXiv:2204.02949], we presented two gauge anomaly-free U(1) models-one based on the Green-Schwarz (GS) anomaly cancellation mechanism, and the other on a grand unified theory (GUT) framework with gauge kinetic mixing-where a heavy leptophobic Z ′ is present along with right-handed neutrinos (N R). We pointed out the interesting possibility of a correlated search for Z ′ and N R at the LHC through the pp → Z ′ → N R N R channel. This channel can probe a part of the Z ′ parameter space beyond the reach of the standard dijet resonance searches. In this follow-up paper, we analyse the challenging monolepton final state arising from the decays of the N R pair with Deep Learning. We present the high-luminosity LHC discovery reaches for six different GUT embeddings and a benchmark point in the GS setup. We also update our previous estimates in the dilepton channel with Deep Learning. We identify parameter regions that can be probed with the proposed channel but will remain inaccessible to dijet searches at the HL-LHC.
In the left-right symmetric models, a heavy charged gauge boson W 0 can decay to a lepton and a r... more In the left-right symmetric models, a heavy charged gauge boson W 0 can decay to a lepton and a righthanded neutrino (RHN). If the neutrino masses are generated through the standard type-I seesaw mechanism, the Yukawa couplings controlling two-body decays of the RHN become very small. As a result, the RHN decays to another lepton and a pair of jets via an off-shell W 0. This is the basis of the Keung-Senjanović (KS) process, which was originally proposed as a probe of lepton number violation at the LHC. However, if a different mechanism like the inverse seesaw generates the neutrino masses, a TeV-scale RHN can have large Yukawa couplings and hence dominantly decay to a lepton and a W boson, leading to a kinematically different process from the KS one. We investigate the prospect of this unexplored process as a probe of the inverse seesaw mechanism in the left-right symmetric models at the High Luminosity LHC (HL-LHC). Our signal arises from the Drell-Yan production of a W 0 and leads to two high-p T same-flavour-opposite-sign leptons and a boosted W-like fatjet in the final state. We find that a sequential W 0 with mass up to ∼6 TeV along with a TeV-scale RHN can be discovered at the HL-LHC.
The Uð1Þ extensions of the Standard Model contain a heavy neutral gauge boson Z 0. If leptophobic... more The Uð1Þ extensions of the Standard Model contain a heavy neutral gauge boson Z 0. If leptophobic, the boson can evade the stringent bounds from the dilepton resonance searches. We consider two theoretically well-motivated examples of leptophobic Uð1Þ extensions in which the Z 0 decays to right-handed neutrinos (RHNs) with substantial branchings. The coexistence of a leptophobic Z 0 and the RHNs opens up a new possibility of searching for these particles simultaneously through the production of a Z 0 at the LHC and its decay to a RHN pair. For this decay to occur, the RHNs need to be lighter than the Z 0. Hence, we study this process in an inverse seesaw setup where the RHNs can be in the TeV range. However, in this case, they have a pseudo-Dirac nature, i.e., a RHN pair would produce only opposite-sign lepton pairs, as opposed to the Majorana-type neutrinos, which can produce both same-and opposite-sign lepton pairs. Hence, the final state we study has a same-flavor opposite-sign lepton pair plus hadronically decaying boosted W bosons. Our analysis shows that the high luminosity LHC can discover a TeV-scale leptophobic Z 0 decaying via a RHN pair in a wide range of available parameters. Interestingly, large parameter regions beyond the reach of future dijet-resonance searches can be probed exclusively through our channel.
We explore an anomaly-free U(1) gauge extended beyond the Standard model (BSM) framework, to acco... more We explore an anomaly-free U(1) gauge extended beyond the Standard model (BSM) framework, to account for the baryon asymmetry of the Universe, along with arranging for tiny neutrino mass. Neutrino masses are generated via higher-dimensional operators (HDOs) involving three right-handed neutrinos (RHNs) with gauge charges (4, 4 and −5 respectively) and two BSM scalars. This is an attractive framework as it can accommodate a keV scale dark matter, with the lightest RHN being the candidate. The remaining two RHNs are quasi-degenerate at the TeV-scale, actively participating in the process of resonant leptogenesis through their decay governed by the same set of HDOs. The RHNs being at the TeV scale, make this framework relevant for studying flavored resonant leptogenesis. This TeV-scale resonant leptogenesis, after satisfying the neutrino oscillation data, leads to interesting predictions on the Yukawa sector of the model HDOs. The thermal evolution of the baryon asymmetry has followed the experimental results rather accurately in that corner of parameter space. As a matter of fact, this TeV-scale framework which in principle relies on the low scale resonant leptogenesis typically leads to predictions that potentially can be tested at the colliders. In particular, we consider the same-sign dilepton signature that arises from the RHN pair production through the decay of heavy gauge boson of the extra U(1).
The current experimental data allow for a sub-TeV colorless weak-singlet scalar or pseudoscalar. ... more The current experimental data allow for a sub-TeV colorless weak-singlet scalar or pseudoscalar. If such a singlet field is present together with TeV-range vectorlike top and bottom partners, there is a possibility that the heavy quarks decay dominantly to the singlet state and a third-generation quark, and the singlet state decays to quark and boson pairs. Such a possibility may arise in various models but it has not been explored experimentally, especially in the context of vectorlike-quark searches. We consider some minimal models, covering the possible weak representations of the top and bottom partners, that can be mapped to many well-motivated ultraviolet-complete theories. We chart out the possible interesting and unexplored signatures of the exotic decay of vectorlike quarks and identify benchmark points representing different signal topologies for the high luminosity LHC. We perform a general scan of the parameter space with the relevant direct search bounds and find that large regions, which do not require any fine-tuning, remain open for the unexplored channels. We also perform a simple projection study in the cleanest channel and indicate how other new but experimentally challenging channels can be used to probe more regions of the parameter space.
Motivated by the persistent anomalies in the semileptonic B-meson decays, we investigate the comp... more Motivated by the persistent anomalies in the semileptonic B-meson decays, we investigate the competency of LHC data to constrain the R D (*)-favoured parameter space in a charge −1/3 scalar leptoquark (S1) model. We consider some scenarios with one large free coupling to accommodate the R D (*) anomalies. As a result, some of them dominantly yield nonresonant τ τ and τ ν events at the LHC through the t-channel S1 exchange. So far, no experiment has searched for leptoquarks using these signatures and the relevant resonant leptoquark searches are yet to put any strong exclusion limit on the parameter space. We recast the latest τ τ and τ ν resonance search data to obtain new exclusion limits. The nonresonant processes strongly interfere (destructively in our case) with the Standard Model background and play the determining role in setting the exclusion limits. To obtain precise limits, we include non-negligible effects coming from the subdominant (resonant) pair and inclusive single leptoquark productions systematically in our analysis. To deal with large destructive interference, we make use of the transverse mass distributions from the experiments in our statistical analysis. In addition, we also recast the relevant direct search results to obtain the most stringent collider bounds on these scenarios to date. These are independent bounds and are competitive to other known bounds. Finally, we indicate how one can adopt these bounds to a wide class of models with S1 that are proposed to accommodate the R D (*) anomalies.
We present the scalar leptoquark pair production process at the LHC computed at the next-to-leadi... more We present the scalar leptoquark pair production process at the LHC computed at the next-to-leading order in QCD, matched to the PYTHIA parton shower using the MC@NLO formalism. We consider the leading order decay of a leptoquark to a lepton (e, µ, τ or νe, νµ, ντ) and a jet and observe the effects of parton shower on the final states. For demonstration, we display the kinametical distributions of a selection of observables along with their scale uncertainties for the 13 TeV LHC. We also present pair production cross sections and K-factors using massless five-quark flavor scheme for different LHC center-of-mass energies. The complete stand-alone code is available online.
In addition to the long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) observab... more In addition to the long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) observables by various independent experiments, the CDF Collaboration has found another significant one in the W-boson mass. These anomalies might be intertwined at a fundamental level and have a single new-physics explanation. In this paper, we present a simultaneous solution to these anomalies with two scalar leptoquarks of roughly equal mass-one weak-singlet S 1 and the other a weak-triplet S 3-which mix through a Higgs portal. The solution has only a few new couplings and TeV-scale leptoquarks, making the solution testable at the LHC. We put a lower and upper bound on the leptoquark masses in this setup from the current LHC data and the assumption that all new couplings are within the perturbative limit.
The possibility of a vectorlike top partner decaying to a new colorless weak-singlet scalar or ps... more The possibility of a vectorlike top partner decaying to a new colorless weak-singlet scalar or pseudoscalar has attracted some attention in the literature. We investigate the production of a weaksinglet charge-2=3 T quark that can decay to a spinless boson (Φ) and a top quark at the LHC. Earlier [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, arXiv:2203.13753.], we showed that in a large part of the parameter space, the T → tΦ and the loopinduced Φ → gg decays become the dominant decay modes for these particles. Here, we investigate the discovery prospects of the T quark in this region through the above decays. In particular, we focus on the pp → TT → ðtΦÞðtΦÞ → ðtðggÞÞðtðggÞÞ channel. Separating this signal from the huge Standard Model background is a challenging task, forcing us to employ a multivariate machine-learning technique. We find that the above channel can be a discovery channel of the top partner in the large part of the parameter space where the above decay chain dominates. Our analysis is largely model independent, and hence our results would be useful in a broad class of new physics models.
The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks c... more The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks considerably. We consider the case of a weak-singlet vectorlike B quark that can decay to a singlet scalar or pseudoscalar Φ. In an earlier paper [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, Phys. Rev. D, 106, 095014 (2022)], we mapped the possibilities to explore such setups at the LHC. We showed that it is possible for a B quark to decay into Φ and the Φ to dominantly decay to a pair of gluons or b quark(s) without fine-tuning the parameters. In this paper, we present a collider search strategy to look for the pair production of singlet B quarks. If both B's decay into bΦ pairs, the final state is fully hadronic: BB → ðbΦÞðbΦÞ → ðbggÞðbggÞ=ðbbbÞðbbbÞ, which is very challenging to probe. Therefore, we consider a simpler mixed decay specific to the singlet B case, BB → ðbΦÞðtWÞ with a lepton in the final state, to achieve the best sensitivity at the high-luminosity LHC. We use a deep neural network with a weighted cross-entropy loss to separate the signal from the huge Standard Model background. Our analysis shows that large areas of the M B − M Φ parameter space are discoverable through this signature. We show how the discovery and exclusion regions scale with the branching ratio in the new decay mode. We also estimate the reach in the inclusive monolepton channel with the same network model.
In addition to the three long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) ob... more In addition to the three long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) observables by various independent experiments, the CDF collaboration has found another significant one in the W boson mass. These anomalies might be intertwined at a fundamental level and have a single new physics explanation. In this paper, we investigate the possibility of whether these anomalies can be explained in a model of a weak-singlet S 1 and a weak-triplet S 3 scalar leptoquarks. We find that with an appropriate flavour ansatz and mass mixing between the S 1 and S 3 leptoquarks through a Higgs portal, the model can explain the four anomalies simultaneously while being consistent with potential spoilsport observables like R νν K (*) .
The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks c... more The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks considerably. We consider the case of a weak-singlet vectorlike B quark that can decay to a singlet scalar or pseudoscalar Φ. In an earlier paper [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, Phys. Rev. D, 106 (2022) 095014; arXiv:2203.13753], we mapped the possibilities to explore such setups at the LHC. We showed that it is possible for a B quark to decay into Φ and the Φ to dominantly decay to a pair of gluons or b quark(s) without fine-tuning the parameters. In this paper, we present a collider search strategy to look for the pair production of singlet B quarks. If both B's decay into bΦ pairs, the final state is fully hadronic: BB → (bΦ)(bΦ) → (bgg)(bgg)/(bbb)(bbb), which is very challenging to probe. Therefore, we consider a simpler mixed decay specific to the singlet B case, BB → (bΦ)(tW) with a lepton in the final state, to achieve the best sensitivity at the highluminosity LHC. We use a deep neural network with a weighted cross-entropy loss to separate the signal from the huge SM background. Our analysis shows that large areas of the MB − MΦ parameter space are discoverable through this signature. We show how the discovery and exclusion regions scale with the branching ratio in the new decay mode. We also estimate the reach in the inclusive monolepton channel with the same network model.
The U(1) extensions of the Standard Model contain a heavy neutral gauge boson Z. If leptophobic, ... more The U(1) extensions of the Standard Model contain a heavy neutral gauge boson Z. If leptophobic, the boson can evade the stringent bounds from the dilepton resonance searches. We consider two theoretically well-motivated examples of leptophobic U(1) extensions in which the Z decays to righthanded neutrinos (RHNs) with substantial branchings. The coexistence of a leptophobic Z and the RHNs opens up a new possibility of searching for these particles simultaneously through the production of a Z at the LHC and its decay to a RHN pair. For this decay to occur, the RHNs need to be lighter than the Z. Hence, we study this process in an inverse seesaw setup where the RHNs can be in the TeV range. However, in this case, they have a pseudo-Dirac nature, i.e., a RHN pair would produce only opposite-sign lepton pairs, as opposed to the Majorana-type neutrinos, which can produce both sameand opposite-sign lepton pairs. Hence, the final state we study has a same-flavour opposite-sign lepton pair plus hadronically-decaying boosted W bosons. Our analysis shows that the high luminosity LHC can discover a TeV-scale leptophobic Z decaying via a RHN pair in a wide range of available parameters. Interestingly, large parameter regions beyond the reach of future dijet-resonance searches can be probed exclusively through our channel.
This is a summary of the activities of the Physics at the LHC working group in the XIth Workshop ... more This is a summary of the activities of the Physics at the LHC working group in the XIth Workshop on High Energy Physics Phenomenology (WHEPP-XI) held at the Physical Research Laboratory, Ahmedabad, India in January 2010. We discuss the activities of each sub-working group on physics issues at colliders such as Tevatron and Large Hadron Collider (LHC). The main issues discussed involve (1) results on W mass measurement and associated QCD uncertainties, (2) an attempt to understand the asymmetry measured at Tevatron in the top quark production, and (3) phenomenology of warped space dimension model.
We investigate a SO(10) grand unification scenario where the complex 10-dimensional scalar multip... more We investigate a SO(10) grand unification scenario where the complex 10-dimensional scalar multiplet, containing the Standard Model (SM) Higgs boson, resides at the TeV scale altogether. The resulting low-energy model is a 2-Higgs-doublet model augmented with two S1-type leptoquarks. The gauge-coupling unification is achieved with only one intermediate scale at which the Pati-Salam gauge group is broken down to the SM. A U (1)PQ global symmetry is also introduced, with the corresponding axion providing a solution to the strong CP problem while also being an important dark matter candidate. The proton-destabilising couplings of the light leptoquarks are forbidden by a discrete symmetry. We discuss how the simultaneous explanation for the R K (*) , R D (*) , and aµ anomalies comes about in the model, and investigate its phenomenological implications.
The current experimental data allow for a sub-TeV colourless weak-singlet scalar or pseudoscalar.... more The current experimental data allow for a sub-TeV colourless weak-singlet scalar or pseudoscalar. If such a singlet field is present together with TeV-range vector-like top and bottom partners, there is a possibility that the heavy quarks decay dominantly to the singlet state and a third-generation quark, and the singlet state can decay to quark and boson pairs. Such a possibility may arise in various models but has not been explored experimentally, especially in the context of the vectorlike-quark searches. We consider some minimal models, covering the possible weak representations of the top and bottom partners, that can be mapped to many well-motivated ultra-violate complete theories. We chart out the possible interesting and unexplored signatures of the exotic decay of vector-like quarks and identify benchmark points representing different signal topologies for high luminosity LHC. We perform a general scan of the parameter space with the relevant direct search bounds and find that large regions, which do not require any fine-tuning, remain open for the unexplored channels. We also perform a simple projection study in the cleanest channel and indicate how other new but experimentally challenging channels can be used to probe more regions of the parameter space.
The LHC search strategies for leptoquarks that couple dominantly to the top quark are different t... more The LHC search strategies for leptoquarks that couple dominantly to the top quark are different than the ones that couple mostly to light quarks. We consider TeV-scale charge 1/3 (φ1) and 5/3 (φ5) scalar leptoquarks that can decay to a top quark and a charged lepton pair (tℓ) giving rise to a resonance system with a boosted top quark and a high-pT lepton at the LHC. We implement a search strategy for these leptoquarks with a signal that is a combination of pair and single production channels by selecting events with at least one hadronically decaying boosted top and two high-pT same flavour opposite sign leptons. While the pair production is best for discovery in the lower mass region, our combined signal can substantially improve the LHC discovery reach as single productions generally overcome pair production in the high mass region. Contrary to the general consensus, we find that the single production of topphilic φ = {φ1, φ5} in association with a lepton and jets could be significant for order one φtℓ coupling if φ couples to a left-handed top quark. Our estimate shows that the leptoquark searches in the tℓℓ + X channel can discover a scalar leptoquark as heavy as 2.1 TeV with 5σ significance for some coupling configurations at the 14 TeV HL-LHC.
A leptophobic Z ′ that does not couple with the Standard Model leptons can evade the stringent bo... more A leptophobic Z ′ that does not couple with the Standard Model leptons can evade the stringent bounds from the dilepton-resonance searches. In our earlier paper [T. Arun et al., Search for the Z ′ boson decaying to a right-handed neutrino pair in leptophobic U(1) models, Phys. Rev. D, 106 (2022) 095035; arXiv:2204.02949], we presented two gauge anomaly-free U(1) models-one based on the Green-Schwarz (GS) anomaly cancellation mechanism, and the other on a grand unified theory (GUT) framework with gauge kinetic mixing-where a heavy leptophobic Z ′ is present along with right-handed neutrinos (N R). We pointed out the interesting possibility of a correlated search for Z ′ and N R at the LHC through the pp → Z ′ → N R N R channel. This channel can probe a part of the Z ′ parameter space beyond the reach of the standard dijet resonance searches. In this follow-up paper, we analyse the challenging monolepton final state arising from the decays of the N R pair with Deep Learning. We present the high-luminosity LHC discovery reaches for six different GUT embeddings and a benchmark point in the GS setup. We also update our previous estimates in the dilepton channel with Deep Learning. We identify parameter regions that can be probed with the proposed channel but will remain inaccessible to dijet searches at the HL-LHC.
In the left-right symmetric models, a heavy charged gauge boson W 0 can decay to a lepton and a r... more In the left-right symmetric models, a heavy charged gauge boson W 0 can decay to a lepton and a righthanded neutrino (RHN). If the neutrino masses are generated through the standard type-I seesaw mechanism, the Yukawa couplings controlling two-body decays of the RHN become very small. As a result, the RHN decays to another lepton and a pair of jets via an off-shell W 0. This is the basis of the Keung-Senjanović (KS) process, which was originally proposed as a probe of lepton number violation at the LHC. However, if a different mechanism like the inverse seesaw generates the neutrino masses, a TeV-scale RHN can have large Yukawa couplings and hence dominantly decay to a lepton and a W boson, leading to a kinematically different process from the KS one. We investigate the prospect of this unexplored process as a probe of the inverse seesaw mechanism in the left-right symmetric models at the High Luminosity LHC (HL-LHC). Our signal arises from the Drell-Yan production of a W 0 and leads to two high-p T same-flavour-opposite-sign leptons and a boosted W-like fatjet in the final state. We find that a sequential W 0 with mass up to ∼6 TeV along with a TeV-scale RHN can be discovered at the HL-LHC.
The Uð1Þ extensions of the Standard Model contain a heavy neutral gauge boson Z 0. If leptophobic... more The Uð1Þ extensions of the Standard Model contain a heavy neutral gauge boson Z 0. If leptophobic, the boson can evade the stringent bounds from the dilepton resonance searches. We consider two theoretically well-motivated examples of leptophobic Uð1Þ extensions in which the Z 0 decays to right-handed neutrinos (RHNs) with substantial branchings. The coexistence of a leptophobic Z 0 and the RHNs opens up a new possibility of searching for these particles simultaneously through the production of a Z 0 at the LHC and its decay to a RHN pair. For this decay to occur, the RHNs need to be lighter than the Z 0. Hence, we study this process in an inverse seesaw setup where the RHNs can be in the TeV range. However, in this case, they have a pseudo-Dirac nature, i.e., a RHN pair would produce only opposite-sign lepton pairs, as opposed to the Majorana-type neutrinos, which can produce both same-and opposite-sign lepton pairs. Hence, the final state we study has a same-flavor opposite-sign lepton pair plus hadronically decaying boosted W bosons. Our analysis shows that the high luminosity LHC can discover a TeV-scale leptophobic Z 0 decaying via a RHN pair in a wide range of available parameters. Interestingly, large parameter regions beyond the reach of future dijet-resonance searches can be probed exclusively through our channel.
We explore an anomaly-free U(1) gauge extended beyond the Standard model (BSM) framework, to acco... more We explore an anomaly-free U(1) gauge extended beyond the Standard model (BSM) framework, to account for the baryon asymmetry of the Universe, along with arranging for tiny neutrino mass. Neutrino masses are generated via higher-dimensional operators (HDOs) involving three right-handed neutrinos (RHNs) with gauge charges (4, 4 and −5 respectively) and two BSM scalars. This is an attractive framework as it can accommodate a keV scale dark matter, with the lightest RHN being the candidate. The remaining two RHNs are quasi-degenerate at the TeV-scale, actively participating in the process of resonant leptogenesis through their decay governed by the same set of HDOs. The RHNs being at the TeV scale, make this framework relevant for studying flavored resonant leptogenesis. This TeV-scale resonant leptogenesis, after satisfying the neutrino oscillation data, leads to interesting predictions on the Yukawa sector of the model HDOs. The thermal evolution of the baryon asymmetry has followed the experimental results rather accurately in that corner of parameter space. As a matter of fact, this TeV-scale framework which in principle relies on the low scale resonant leptogenesis typically leads to predictions that potentially can be tested at the colliders. In particular, we consider the same-sign dilepton signature that arises from the RHN pair production through the decay of heavy gauge boson of the extra U(1).
The current experimental data allow for a sub-TeV colorless weak-singlet scalar or pseudoscalar. ... more The current experimental data allow for a sub-TeV colorless weak-singlet scalar or pseudoscalar. If such a singlet field is present together with TeV-range vectorlike top and bottom partners, there is a possibility that the heavy quarks decay dominantly to the singlet state and a third-generation quark, and the singlet state decays to quark and boson pairs. Such a possibility may arise in various models but it has not been explored experimentally, especially in the context of vectorlike-quark searches. We consider some minimal models, covering the possible weak representations of the top and bottom partners, that can be mapped to many well-motivated ultraviolet-complete theories. We chart out the possible interesting and unexplored signatures of the exotic decay of vectorlike quarks and identify benchmark points representing different signal topologies for the high luminosity LHC. We perform a general scan of the parameter space with the relevant direct search bounds and find that large regions, which do not require any fine-tuning, remain open for the unexplored channels. We also perform a simple projection study in the cleanest channel and indicate how other new but experimentally challenging channels can be used to probe more regions of the parameter space.
Motivated by the persistent anomalies in the semileptonic B-meson decays, we investigate the comp... more Motivated by the persistent anomalies in the semileptonic B-meson decays, we investigate the competency of LHC data to constrain the R D (*)-favoured parameter space in a charge −1/3 scalar leptoquark (S1) model. We consider some scenarios with one large free coupling to accommodate the R D (*) anomalies. As a result, some of them dominantly yield nonresonant τ τ and τ ν events at the LHC through the t-channel S1 exchange. So far, no experiment has searched for leptoquarks using these signatures and the relevant resonant leptoquark searches are yet to put any strong exclusion limit on the parameter space. We recast the latest τ τ and τ ν resonance search data to obtain new exclusion limits. The nonresonant processes strongly interfere (destructively in our case) with the Standard Model background and play the determining role in setting the exclusion limits. To obtain precise limits, we include non-negligible effects coming from the subdominant (resonant) pair and inclusive single leptoquark productions systematically in our analysis. To deal with large destructive interference, we make use of the transverse mass distributions from the experiments in our statistical analysis. In addition, we also recast the relevant direct search results to obtain the most stringent collider bounds on these scenarios to date. These are independent bounds and are competitive to other known bounds. Finally, we indicate how one can adopt these bounds to a wide class of models with S1 that are proposed to accommodate the R D (*) anomalies.
We present the scalar leptoquark pair production process at the LHC computed at the next-to-leadi... more We present the scalar leptoquark pair production process at the LHC computed at the next-to-leading order in QCD, matched to the PYTHIA parton shower using the MC@NLO formalism. We consider the leading order decay of a leptoquark to a lepton (e, µ, τ or νe, νµ, ντ) and a jet and observe the effects of parton shower on the final states. For demonstration, we display the kinametical distributions of a selection of observables along with their scale uncertainties for the 13 TeV LHC. We also present pair production cross sections and K-factors using massless five-quark flavor scheme for different LHC center-of-mass energies. The complete stand-alone code is available online.
In addition to the long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) observab... more In addition to the long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) observables by various independent experiments, the CDF Collaboration has found another significant one in the W-boson mass. These anomalies might be intertwined at a fundamental level and have a single new-physics explanation. In this paper, we present a simultaneous solution to these anomalies with two scalar leptoquarks of roughly equal mass-one weak-singlet S 1 and the other a weak-triplet S 3-which mix through a Higgs portal. The solution has only a few new couplings and TeV-scale leptoquarks, making the solution testable at the LHC. We put a lower and upper bound on the leptoquark masses in this setup from the current LHC data and the assumption that all new couplings are within the perturbative limit.
The possibility of a vectorlike top partner decaying to a new colorless weak-singlet scalar or ps... more The possibility of a vectorlike top partner decaying to a new colorless weak-singlet scalar or pseudoscalar has attracted some attention in the literature. We investigate the production of a weaksinglet charge-2=3 T quark that can decay to a spinless boson (Φ) and a top quark at the LHC. Earlier [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, arXiv:2203.13753.], we showed that in a large part of the parameter space, the T → tΦ and the loopinduced Φ → gg decays become the dominant decay modes for these particles. Here, we investigate the discovery prospects of the T quark in this region through the above decays. In particular, we focus on the pp → TT → ðtΦÞðtΦÞ → ðtðggÞÞðtðggÞÞ channel. Separating this signal from the huge Standard Model background is a challenging task, forcing us to employ a multivariate machine-learning technique. We find that the above channel can be a discovery channel of the top partner in the large part of the parameter space where the above decay chain dominates. Our analysis is largely model independent, and hence our results would be useful in a broad class of new physics models.
The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks c... more The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks considerably. We consider the case of a weak-singlet vectorlike B quark that can decay to a singlet scalar or pseudoscalar Φ. In an earlier paper [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, Phys. Rev. D, 106, 095014 (2022)], we mapped the possibilities to explore such setups at the LHC. We showed that it is possible for a B quark to decay into Φ and the Φ to dominantly decay to a pair of gluons or b quark(s) without fine-tuning the parameters. In this paper, we present a collider search strategy to look for the pair production of singlet B quarks. If both B's decay into bΦ pairs, the final state is fully hadronic: BB → ðbΦÞðbΦÞ → ðbggÞðbggÞ=ðbbbÞðbbbÞ, which is very challenging to probe. Therefore, we consider a simpler mixed decay specific to the singlet B case, BB → ðbΦÞðtWÞ with a lepton in the final state, to achieve the best sensitivity at the high-luminosity LHC. We use a deep neural network with a weighted cross-entropy loss to separate the signal from the huge Standard Model background. Our analysis shows that large areas of the M B − M Φ parameter space are discoverable through this signature. We show how the discovery and exclusion regions scale with the branching ratio in the new decay mode. We also estimate the reach in the inclusive monolepton channel with the same network model.
In addition to the three long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) ob... more In addition to the three long-standing anomalies seen in the muon g − 2, R K (*) , and R D (*) observables by various independent experiments, the CDF collaboration has found another significant one in the W boson mass. These anomalies might be intertwined at a fundamental level and have a single new physics explanation. In this paper, we investigate the possibility of whether these anomalies can be explained in a model of a weak-singlet S 1 and a weak-triplet S 3 scalar leptoquarks. We find that with an appropriate flavour ansatz and mass mixing between the S 1 and S 3 leptoquarks through a Higgs portal, the model can explain the four anomalies simultaneously while being consistent with potential spoilsport observables like R νν K (*) .
The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks c... more The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks considerably. We consider the case of a weak-singlet vectorlike B quark that can decay to a singlet scalar or pseudoscalar Φ. In an earlier paper [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, Phys. Rev. D, 106 (2022) 095014; arXiv:2203.13753], we mapped the possibilities to explore such setups at the LHC. We showed that it is possible for a B quark to decay into Φ and the Φ to dominantly decay to a pair of gluons or b quark(s) without fine-tuning the parameters. In this paper, we present a collider search strategy to look for the pair production of singlet B quarks. If both B's decay into bΦ pairs, the final state is fully hadronic: BB → (bΦ)(bΦ) → (bgg)(bgg)/(bbb)(bbb), which is very challenging to probe. Therefore, we consider a simpler mixed decay specific to the singlet B case, BB → (bΦ)(tW) with a lepton in the final state, to achieve the best sensitivity at the highluminosity LHC. We use a deep neural network with a weighted cross-entropy loss to separate the signal from the huge SM background. Our analysis shows that large areas of the MB − MΦ parameter space are discoverable through this signature. We show how the discovery and exclusion regions scale with the branching ratio in the new decay mode. We also estimate the reach in the inclusive monolepton channel with the same network model.
The U(1) extensions of the Standard Model contain a heavy neutral gauge boson Z. If leptophobic, ... more The U(1) extensions of the Standard Model contain a heavy neutral gauge boson Z. If leptophobic, the boson can evade the stringent bounds from the dilepton resonance searches. We consider two theoretically well-motivated examples of leptophobic U(1) extensions in which the Z decays to righthanded neutrinos (RHNs) with substantial branchings. The coexistence of a leptophobic Z and the RHNs opens up a new possibility of searching for these particles simultaneously through the production of a Z at the LHC and its decay to a RHN pair. For this decay to occur, the RHNs need to be lighter than the Z. Hence, we study this process in an inverse seesaw setup where the RHNs can be in the TeV range. However, in this case, they have a pseudo-Dirac nature, i.e., a RHN pair would produce only opposite-sign lepton pairs, as opposed to the Majorana-type neutrinos, which can produce both sameand opposite-sign lepton pairs. Hence, the final state we study has a same-flavour opposite-sign lepton pair plus hadronically-decaying boosted W bosons. Our analysis shows that the high luminosity LHC can discover a TeV-scale leptophobic Z decaying via a RHN pair in a wide range of available parameters. Interestingly, large parameter regions beyond the reach of future dijet-resonance searches can be probed exclusively through our channel.
This is a summary of the activities of the Physics at the LHC working group in the XIth Workshop ... more This is a summary of the activities of the Physics at the LHC working group in the XIth Workshop on High Energy Physics Phenomenology (WHEPP-XI) held at the Physical Research Laboratory, Ahmedabad, India in January 2010. We discuss the activities of each sub-working group on physics issues at colliders such as Tevatron and Large Hadron Collider (LHC). The main issues discussed involve (1) results on W mass measurement and associated QCD uncertainties, (2) an attempt to understand the asymmetry measured at Tevatron in the top quark production, and (3) phenomenology of warped space dimension model.
We investigate a SO(10) grand unification scenario where the complex 10-dimensional scalar multip... more We investigate a SO(10) grand unification scenario where the complex 10-dimensional scalar multiplet, containing the Standard Model (SM) Higgs boson, resides at the TeV scale altogether. The resulting low-energy model is a 2-Higgs-doublet model augmented with two S1-type leptoquarks. The gauge-coupling unification is achieved with only one intermediate scale at which the Pati-Salam gauge group is broken down to the SM. A U (1)PQ global symmetry is also introduced, with the corresponding axion providing a solution to the strong CP problem while also being an important dark matter candidate. The proton-destabilising couplings of the light leptoquarks are forbidden by a discrete symmetry. We discuss how the simultaneous explanation for the R K (*) , R D (*) , and aµ anomalies comes about in the model, and investigate its phenomenological implications.
The current experimental data allow for a sub-TeV colourless weak-singlet scalar or pseudoscalar.... more The current experimental data allow for a sub-TeV colourless weak-singlet scalar or pseudoscalar. If such a singlet field is present together with TeV-range vector-like top and bottom partners, there is a possibility that the heavy quarks decay dominantly to the singlet state and a third-generation quark, and the singlet state can decay to quark and boson pairs. Such a possibility may arise in various models but has not been explored experimentally, especially in the context of the vectorlike-quark searches. We consider some minimal models, covering the possible weak representations of the top and bottom partners, that can be mapped to many well-motivated ultra-violate complete theories. We chart out the possible interesting and unexplored signatures of the exotic decay of vector-like quarks and identify benchmark points representing different signal topologies for high luminosity LHC. We perform a general scan of the parameter space with the relevant direct search bounds and find that large regions, which do not require any fine-tuning, remain open for the unexplored channels. We also perform a simple projection study in the cleanest channel and indicate how other new but experimentally challenging channels can be used to probe more regions of the parameter space.
The LHC search strategies for leptoquarks that couple dominantly to the top quark are different t... more The LHC search strategies for leptoquarks that couple dominantly to the top quark are different than the ones that couple mostly to light quarks. We consider TeV-scale charge 1/3 (φ1) and 5/3 (φ5) scalar leptoquarks that can decay to a top quark and a charged lepton pair (tℓ) giving rise to a resonance system with a boosted top quark and a high-pT lepton at the LHC. We implement a search strategy for these leptoquarks with a signal that is a combination of pair and single production channels by selecting events with at least one hadronically decaying boosted top and two high-pT same flavour opposite sign leptons. While the pair production is best for discovery in the lower mass region, our combined signal can substantially improve the LHC discovery reach as single productions generally overcome pair production in the high mass region. Contrary to the general consensus, we find that the single production of topphilic φ = {φ1, φ5} in association with a lepton and jets could be significant for order one φtℓ coupling if φ couples to a left-handed top quark. Our estimate shows that the leptoquark searches in the tℓℓ + X channel can discover a scalar leptoquark as heavy as 2.1 TeV with 5σ significance for some coupling configurations at the 14 TeV HL-LHC.
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Papers by Tanumoy Mandal