Many new physics models predict resonances with masses in the TeV range which decay into a pair of top quarks. With its large cross section, t-bar t production at the Large Hadron Collider (LHC) offers an excellent opportunity to search for such particles. We present a detailed study of the discovery potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu b-bar bq-bar q' (ell=e, mu) final state. We utilize final states with one or two tagged b-quarks, and two, three or four jets (including b-jets). Our calculations take into account the finite resolution of detectors, the energy loss due to b-quark decays, the expected reduced b-tagging efficiency at large t-bar t invariant masses, and include the background originating from Wb-bar b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios, and compare them with those for KK gravitons, and a Z_H boson in the Littlest Higgs model. We also analyze the capabilities of the LHC experiments to differentiate between individual KK gluon models and measure the couplings of KK gluons to quarks. We find that, for the parameters and models chosen, KK gluons with masses up to about 4 TeV can be discovered at the LHC. The ability of the LHC to discriminate between different bulk RS models, and to measure the couplings of the KK gluons is found to be highly model dependent.
We explore the possibility of searching for axionlike particle (ALP) by $ep$ collisions via the subprocess $e^{-}γ\rightarrow e^{-}a \rightarrow e^{-}γγ$. Sensitivities to the effective ALP-photon coupling $g_{aγγ}$ for its mass in the range of 10 GeV $< M_{a}< 3$ TeV are obtained for the LHeC and its high-energy upgrade, FCC-eh. Comparing to existing bounds on the ALP free parameters, we find that the bounds given by $ep$ colliders are competitive and complementary to other colliders.
We investigate the prospects for discovering axion-like particles (ALPs) via a light-by-light (LBL) scattering at two colliders, the future circular collider (FCC-ee) and circular electron-positron collider (CEPC). The promising sensitivities to the effective ALP-photon coupling $g_{aγγ}$ are obtained. Our numerical results show that the FCC-ee and CEPC might be more sensitive to the ALPs with mass 2 GeV $\sim$ 10 GeV than the LHC and CLIC.
We investigate the production of fourth generation neutrino in the context of new $e ν_4 W$ magnetic dipole moment type interaction in $ep$ collisions at the future lepton-hadron colliders. We have obtained the mass limits of 700 GeV for THERA ($\sqrt S$=1 TeV) and 2.8 TeV for LC$\otimes$ LHC ($\sqrt S$=3.74 TeV).
We discuss the production of new matter particles that are predicted by many extensions of the Standard Model, at future high--energy pp, eP and $e^+e^-$ linear colliders. We focus on the case of exotic, excited and di--fermions. Talk given at "Beyond the Standard Model IV", Lake Tahoe, Ca., December 1994.
We examine the sensitivity of the process e+e- -> nu nubar + gamma to additional W-like bosons which arise in various models. The process is found to be sensitive to W' masses up to several TeV.
We discuss the possibility of the existence of a long-lived top squark ($τ\ll 10^{10} years$) and its motivation. If the stop is indeed metastable, it forms hadrons. We study properties of the low-energy stop-containing hadrons and their signatures in collider experiments.
Lorentz violation has been a popular field in recent years in the search for new physics beyond the Standard Model. We present a general method to build all Lorentz-violating terms in gauge field theories, including ones involving operators of arbitrary mass dimension. Applying these results to two types of experiments in high-energy colliders, light-by-light scattering and deep-inelastic scattering, we extract first bounds on certain coefficients for Lorentz violation.
Axion-like particles are an important part of the spectrum of anomalous gauge theories involving modified mechanisms of cancellation of the gauge anomalies. Among these are intersecting brane models, which are characterized by the presence of one physical axion. We overview a recent study of their supersymmetric construction and some LHC studies of the productions rates for a gauged axion.
We correct our treatment of decays of the lightest chargino to final states containing the lightest neutralino in the case where the chargino and neutralino masses differ by less than 1 GeV. A brief summary of the phenomenological implications is given.
We investigate the potential of a high-energy $γγ$ collider to detect an anomalous $\bar t q γ$ coupling from observation of the reaction $γγ\to t\bar q$, $\bar t q$, where $q=c$ or $u$. We find that with $b$-tagging and suitable kinematic cuts this process should be observable if the anomalous coupling $κ/Λ$ is no less than about 0.05/TeV, where $Λ$ is the scale of new physics associated with the anomalous interaction. This improves upon the bound possible from observation of top decays at the Tevatron.
A high energy muon collider can provide new and complementary discovery potential to the LHC or future hadron colliders. Leptoquarks are a motivated class of exotic new physics models, with distinct production channels at hadron and lepton machines. We study a vector leptoquark model at a muon collider with $\sqrt{s} = 3, 14$ TeV within a set of both UV and phenomenologically motivated flavor scenarios. We compute which production mechanism has the greatest reach for various values of the leptoquark mass and the coupling between leptoquark and Standard Model fermions. We find that we can probe…
Considering the theoretical constraints on the charged-current (CC) non-standard neutrino interaction (NSI) parameters in a simplified $W'$ model, we study the sensitivities of the Large Hadron electron Collider (LHeC) and Future Circular Collider-hadron electron (FCC-he) to the CC NSI parameters through the subprocess $e^{-}q \to W' \to v_{e}q'$. Our results show that the LHeC with $\mathcal{L} = 100\;{\rm fb}^{-1}$ is a little more sensitive to the CC NSI parameters than that of the high-luminosity (HL) LHC, and the absolute values of the lower limits on the CC NSI parameters at the FCC-he a…
I overview the status of the Electroweak Symmetry Breaking problem, paying special attention to the possible signals of new physics at the Large Hadron Collider (and at a Linear Collider)
The Georgi-Machacek model is one of many beyond Standard Model scenarios with an extended scalar sector which can group under the custodial $\rm SU(2)_C$ symmetry. There are 5-plet, 3-plet and singlet Higgs bosons under the classification of such symmetry in addition to the Standard Model Higgs boson. In this paper, we study the prospects for detecting the doubly-charged Higgs boson ($\rm H_5^{\pm\pm}$) through the vector boson fusion production at the electron-proton (ep) colliders. We concentrate on our analysis through $μ$-lepton pair production via pair of same-sign W bosons decay. The $\r…
If the Higgs is produced with a large enough cross section in the {\em exclusive} reaction $p + \bar{p} \to p + H + \bar{p}$ it will give rise to a peak at $M_H$ in the {\em missing mass} ($MM$) spectrum, calculated from the 4-momenta of the beam particles and the outgoing $p$ and $\bar{p}$. The resolution in $MM$ can be approximately 250 MeV, independent of $M_H$ from 100 GeV to 200 GeV. This high resolution makes a search feasible over nearly this full mass range at the Tevatron with 15 fb$^{-1}$ as hoped for in Run II.
We discuss the parity-violating left-right asymmetries (LRAs) in Möller scattering at the International Linear Collider (ILC) induced by doubly charged Higgs bosons in models with $SU(2)_L$ triplet and singlet scalar bosons, which couple to the left- and right-handed charged leptons, respectively. These bosons are important in the scenarios for the generation of the neutrino mass. We demonstrate that the contributions to the LRAs from the triplet and singlet bosons are opposite to each other. In particular, we show that the doubly charged Higgs boson from the singlet scalar can be tested at th…
We consider theories where lepton flavor is violated, in particular concentrating on the four fermion operator consisting of three electrons and a tau. Strong constraints are available from existing searches for tau -> eee, requiring the scale of the contact interaction to be less than ~(9 TeV)^-2. We reexamine this type of physics, assuming that the particles responsible are heavy (with masses greater than ~TeV) such that a contact interaction description continues to be applicable at the energies for a future e+e- collider. We find that the process e+e- -> e tau can be a very sensitive probe…
We investigate the prospects for the discovery of massive color-octet vector bosons at the CERN Large Hadron Collider with $\sqrt{s} = 14$ TeV. A phenomenological Lagrangian is adopted to evaluate the cross section of a pair of colored vector bosons (colorons, $\tildeρ$) decaying into four colored scalar resonances (hyper-pions, $\tildeπ$), which then decay into eight gluons. We include the dominant physics background from the production of $8g,7g1q, 6g2q$, and $5g3q$, and determine the masses of $\tildeπ$ and $\tildeρ$ where discovery is possible. For example, we find that a 5$σ$ signal can b…
Theories of quantum gravity suggest the existence of a minimal length scale. It is interesting to speculate what the consequences of the existence of such a length scale would be for models of large extra dimensions, in particular, the ADD model. When ADD model is conflated with the minimal length scale scenario, processes involving virtual exhange of gravitons cease to be ulraviolent divergent. We study the production of dileptons at hadron colliders as an example of a process mediated by virtual gravitons. We find that the bounds we derive on the effective string scale are significantly diff…
Weak singlet charged scalar exists in many new physics models beyond the Standard Model. In this work we show that a light singlet charged scalar with mass above 65~GeV is still allowed by the LEP and LHC data. The interactions of the singlet charged scalar with the Standard Model particles are described by operators up to dimension-5. Dominant decay modes of the singlet charged scalar are obtained, and a subtlety involving field redefinition and gauge fixing due to a dimension-5 operator is also clarified. We demonstrate that it is promising to observe the singlet charged scalar at the LHC.
Lepton flavor violating interactions are absent in the standard model but are expected in various beyond standard models. In this work, the potential of the future circular electron-positron collider to probe the four fermion lepton flavor couplings via the $e^{+}e^{-}\rightarrow e^{\pm}τ^{\mp}$ process is revisited by means of an effective field theory approach. We provide constraints at $95\%$ CL on the dimension-six Wilson coefficients including major sources of background processes and considering realistic detector effects at four expected operation energies $\sqrt{s}=157.5$, $162.5$, $24…
While it is natural for supersymmetric particles to be well within the mass range of the large hadron collider, it is possible that the sparticle masses could be very heavy. Signatures are examined at a very high energy hadron collider and an very high luminosity option for the Large Hadron Collider in such scenarios.
The Georgi-Machacek model is one of many beyond Standard Model scenarios with an extended scalar sector which can group under the custodial $\rm SU(2)_C$ symmetry. There are 5-plet, 3-plet and singlet Higgs bosons under the classification of such symmetry in addition to the Standard Model Higgs boson. Here we study the prospects for detecting the doubly-charged Higgs boson ($\rm H_5^{\pm\pm}$) through the vector boson fusion production at the electron-proton colliders. Typically, we concentrate on our analysis through $μ$-lepton pair production via pair of same-sign W bosons decay. The discove…
This talk gives a brief introduction to open questions in jet physics and QCD which come to the fore in the high-luminosity regime characterizing the upcoming phase of the Large Hadron Collider and future hadron colliders.
Upon assuming the $B-L$ Supersymmetric Standard Model (BLSSM) as theoretical framework accommodating a multi-Higgs sector, we assess the scope of the High Luminosity Large Hadron Collider (HL-LHC) in accessing charged Higgs bosons ($H^\pm$) produced in pairs from $Z'$ decays. We show that, by pursuing both di-jet and tau-neutrino decays, several signals can be established for $H^\pm$ masses ranging from about $M_{W}$ to above $m_t$ and $Z'$ masses between 2.5 TeV and 3.5 TeV. The discovery can be attained, even in a background free environment in some cases, owing to the fact that the very mas…
In this work, we propose a possible experimental research topic on the $Υ(6S)\to Υ(nS)η^{(\prime)}$ ($n=1,2,3$) transitions. Considering the hadronic loop effect from the intermediate $S$-wave $B_{(s)}$ and $B_{(s)}^*$ mesons, we estimate the partial decay widths and the corresponding branching ratios of the $Υ(6S)\to Υ(nS)η^{(\prime)}$ hadronic decays, which become considerably large. With the running of the Belle II experiment, it becomes possible to explore these $Υ(6S)\to Υ(nS)η^{(\prime)}$ transitions.
We investigate nonfactorizable contributions to charm meson decays in $ D \rightarrow \bar K π$/ $ \bar K ρ$ /$ \bar K ^{*} π$ / $ \bar K a_{1}$ / $ \bar K ^{*} ρ$ modes. Obtaining the contributions from spectator-quark diagrams for $ N_{c}$ = 3, we determine nonfactorizable isospin 1/2 and 3/2 amplitudes required to explain the data for these modes. We observe that ratio of these amplitudes seem to follow a universal value.
We point out that a study of event shapes at hadron colliders allows to explore novel aspects of QCD. These studies are today made easier by the development of a program which automates the resummation.
The LHCb Collaboration recently gave an update on testing lepton flavour universality with $B^+ \rightarrow K^+ \ell^+ \ell^-$, in which a 3.1 standard deviations from the standard model prediction was observed. The g-2 experiment also reports a 3.3 standard deviations from the standard model on muon anomalous magnetic moment measurement. These deviations could be explained by introducing new particles including leptoquarks. In this paper, we show the possibility to search for heavy spin-1 leptoquarks at a future TeV scale muon collider by performing studies from three channels: 1) same flavou…
A compilation is given of the pair production cross sections for scalar and vector leptoquarks in the kinematic range of the hadron colliders Tevatron and LHC.
I discuss the impact of the the coherent parton radiation on semi-inclusive production of hadrons in deep inelastic scattering at lepton-proton colliders. Such radiation can be consistently described in the $b$-space resummation formalism, which was originally developed to improve theoretical description of production of hadrons at $e^+e^-$ colliders and electroweak vector bosons at hadron-hadron colliders. I present the detailed derivation of the resummed cross section and the energy flow at the next-to-leading order of perturbative QCD. The theoretical results are compared to the experimenta…
The theoretical status of Higgs boson and supersymmetric particle production at hadron colliders is reviewed with particular emphasis on recent results and open problems.
The tau lepton plays important role in the correlation between the low-energy neutrino oscillation data and the lepton flavor structure in heavy neutrino decay. We investigate the lepton flavor signatures with tau lepton at hadron collider through lepton number violating (LNV) processes. In the Type I Seesaw with U$(1)_{\rm B-L}$ extension, we study the pair production of heavy neutrinos via a $Z'$ resonance. We present a detailed assessment of the search sensitivity to the channels with tau lepton in the subsequent decay of heavy neutrinos. For the benchmark model with $Z'$ only coupled to th…
We review the theoretical status of b to s hadronic penguin decays in the Standard Model and beyond. We summarize the main theoretical tools to compute Branching Ratios and CP asymmetries for b to s penguin dominated nonleptonic decays, and discuss the theoretical uncertainties in the prediction of time-dependent CP asymmetries in this processes. We consider general aspects of b to s transitions beyond the Standard Model. Then we present detailed predictions in supersymmetric models with new sources of flavor and CP violation.
To provide context for discussions of experiments at future muon colliders, I survey what is known and what will be known about the top quark and the Higgs boson from experiments at hadron colliders.
This writeup gives an introduction to the theoretical understanding that lies behind automated resummation. It then discusses its applications to hadron-collider event shapes.
We studied the interplay between the mass reach for electroweakinos at future hadron colliders and direct detection experiments. The lack of new phenomena at the LCH motivates us to focus on split supersymmetry scenarios with different electroweakino spectra. A 100 TeV hadron collider may reach masses up to 3 TeV in models of anomaly mediation with long-lived thermal Winos. Moreover, in scenarios where the lightest neutralino is not the only dark matter component, the interplay between collider searches and direct detection experiments might cover large part of the parameter space.
I survey the characteristics of hadron colliders as tools to investigate top-quark physics and to explore the 1-TeV scale of electroweak symmetry breaking.
We report the calculation of next-to-next-to-leading order (NNLO) QCD corrections in the purely gluonic channel to dijet production and related observables at hadron colliders. Our result represents the first NNLO calculation of a massless jet observable at hadron colliders, and opens the path towards precision QCD phenomenology with the LHC.
We study the flavor-changing decay $h\to τμ$ with $τ=τ^-+τ^+$ and $μ=μ^-+μ^+$ of a Higgs boson at future hadron colliders, namely: a) High Luminosity Large Hadron Collider, b) High Energy Large Hadron Collider and c) Future hadron-hadron Circular Collider. The theoretical framework adopted is the Two-Higgs-Doublet Model type III. The free model parameters involved in the calculation are constrained through Higgs boson data, Lepton Flavor Violating processes and the muon anomalous magnetic dipole moment; later they are used to analyze the branching ratio of the decay $h\toτμ$ and to evaluate th…
We discuss theoretical aspects of parton distribution functions for very high energy scattering in relation with upcoming measurements in DIS and hadron-hadron collisions.
The current theoretical understanding of anomalous gauge boson couplings is reviewed, and the direct measurement of these couplings in present and future hadron collider experiments is briefly discussed.
We review the recent theoretical progress in single-top physics at hadron colliders. Apart from single-top production within the Standard Model we treat certain aspects of single-top production in beyond Standard Model scenarios.
We present compact analytic expressions for all one-loop helicity amplitudes contributing to ttbar production at hadron colliders. Using recently developed generalised unitarity methods and a traditional Feynman based approach we produce a fast and flexible implementation.
We investigate the discovery potential of Kaluza-Klein gluons as a dijet resonance at hadron colliders with different center-of-mass energies, from 14 TeV to 33 TeV to 100 TeV. We also present the current bounds from dijet searches at UA2, Tevatron, and LHC.
We present here the results for Higgs and Supersymmetry prospective searches at the Large Hadron Collider. We show that for one year at high luminosity, Standard Model and MSSM Higgs should be observed within the theoretically expected mass range. MSUGRA and restricted phenomenological MSSM searches lead to discovery of up to 2.5 TeV squarks and gluinos.
We compute the pair production cross section of two Kaluza Klein modes in the Randall-Sundrum model at $e^+e^-$ and hadron hadron colliders. These processes are interesting because they get dominant contribution from the graviton interaction at next to leading order. Hence they provide a nontrivial test of the low scale gravity models. All the Feynman rules at next to leading order are also presented. These rules may be useful for many phenomenological applications including the computation of higher order loop corrections.
The International Linear Collider (ILC) will be able to precisely measure the electroweak couplings of the top in e+e- -> tt~. We compare the limits which can be achieved at the ILC with those which can be obtained in tt~gamma$ and tt~Z production at the Large Hadron Collider (LHC).
