New Physics at the Large Hadron Collider

The following sections are included:

• Preface
• Contents

As we consider the tremendous physics reaches of the big future circular electron–positron and proton–proton colliders, it might be advisable to keep a close track of what accelerator challenges they face. Good progresses are being made, and yet it is reported here that substantial investments in funding, manpower, as well as a long sustained time to the R&D efforts will be required in preparation to realize these dream colliders.

The discovery of the Higgs particle is demanding a detailed knowledge of the properties of this fundamental component of the Standard Model. From the available data however, it cannot be concluded yet that we have found the SM Higgs boson and not one of the scalars postulated within the possible extensions of the SM. It is shown that a Higgs factory through a muon collider is particularly appropriate for precision studies of the properties of this particle. However sizable QED radiative effects — of order of 50% — must be carefully taken into account for a precise measurement of the leptonic and total widths of the Higgs particle. The results presented here are mainly based on a recent work in collaboration of Tao Han and Zhen Liu.

With the LHC Run 1 data, the LHCb experiment discovered two pentaquark states and has evidence for a number of possible anomalies in the avour sector. The possible anomalies include indications of violations of lepton avour universality, deviations from Standard Model predictions in several B-meson decay modes that are mediated by avour-changing neutral currents, and further evidence for a discrepancy between inclusive and exclusive measurements of the CKM matrix element |V_ub|.

We present the embedding of the SM gauge group in SO10, a simple, compact unifying gauge group, with each of the three basic spin 1/2 families forming a unitary, irreducible 16-dimensional representation of spin10, which is complex, i.e. chiral. Subtle differences to the mixed representations of SU5, contained in the SO10 scheme, are pointed out. These have consequences for neutrino avors, which become paired in a light SU2_L− active doublet mode and a heavy SM singlet mode, one ν, N– pair per family.

We present an overview of our recent investigations regarding the prospects of ongoing neutrino experiments as well as future experiments in determining few of the most important unknowns in the field of neutrino physics, specifically the neutrino mass ordering and leptonic CP-violation phase. The effect of matter oscillations on the neutrino oscillation probabilities has been exploited in resolving the degeneracy between the neutrino mass ordering and the CP violation phase in the leptonic sector. Further, we estimate the extent of extrinsic CP and CPT violation in the experiments with superbeams as well as neutrino factories.

The present work attempts to provide an overview of texture specific mass matrices, which, along with Weak Basis (WB) transformations, emerge as a viable framework for explaining the fermion masses and mixing data in the quark as well as lepton sector.

Experimental era of rare B-decays started with the measurement of B → K^*γ by CLEO in 1993, followed by the measurement of the inclusive decay B → X_sγ in 1995, which serves as the standard candle in this field. The frontier has moved in the meanwhile to the experiments at the LHC, in particular, LHCb, with the decay B⁰ → μ⁺μ⁻ at about 1 part in 1010 being the smallest branching fraction measured so far. Experimental precision achieved in this area has put the standard model to unprecedented stringent tests and more are in the offing in the near future. I review some key measurements in radiative, semileptonic and leptonic rare B-decays, contrast them with their estimates in the SM, and focus on several mismatches reported recently. They are too numerous to be ignored, yet, standing alone, none of them is significant enough to warrant the breakdown of the SM. Rare B-decays find themselves at the crossroads, possibly pointing to new horizons, but quite likely requiring an improved theoretical description in the context of the SM. An independent precision experiment such as Belle II may help greatly in clearing some of the current experimental issues.

The ATLAS and CMS collaborations have performed studies of a wide range of Standard Model processes using data collected at the Large Hadron Collider at center-of-mass energies of 7, 8 and 13 TeV. These measurements are used to explore the Standard Model in a new kinematic regime, perform precision tests of the model, determine some of its fundamental parameters, constrain the proton parton distribution functions, and study new rare processes observed for the first time. Examples of recent Standard Model measurements performed by the ATLAS and CMS collaborations are summarized in this report. The measurements presented span a wide range of event final states including jets, photons, W/Z bosons, top quarks, and Higgs bosons.

Superconformal algebra leads to remarkable connections between the masses of mesons and baryons of the same parity — supersymmetric relations between the bosonic and fermionic bound states of QCD. Supercharges connect the mesonic eigenstates to their baryonic superpartners, where the mesons have internal angular momentum one unit higher than the baryons: L_M = L_B + 1. The dynamics of the superpartner hadrons also match; for example, the power-law fall-off of the form factors are the same for the mesonic and baryonic superpartners, in agreement with twist counting rules. An effective supersymmetric light-front Hamiltonian for hadrons composed of light quarks can be constructed by embedding superconformal quantum mechanics into AdS space. This procedure also generates a spin–spin interaction between the hadronic constituents. A specific breaking of conformal symmetry inside the graded algebra determines a unique quark-confining light-front potential for light hadrons in agreement with the soft-wall AdS/QCD approach and light-front holography. Only one mass parameter appears; it sets the confinement mass scale, a universal value for the slope of all Regge trajectories, the nonzero mass of the proton and other hadrons in the chiral limit, as well as the length scale which underlies their structure. The mass for the pion eigenstate vanishes in the chiral limit. When one includes the constituent quark masses using the Feynman–Hellman theorem, the predictions are consistent with the empirical features of the light-quark hadronic spectra. Our analysis can be consistently applied to the excitation spectra of the π, ρ, K, K* and ø meson families as well as to the N, Δ, Λ, Σ, Σ*, Ξ and Ξ* baryons. We also predict the existence of tetraquarks which are degenerate in mass with baryons with the same angular momentum. The mass-squared of the light hadrons can be expressed in a universal and frame-independent decomposition of contributions from the constituent kinetic energy, the confinement potential, and spin–spin contributions. We also predict features of hadron dynamics, including hadronic light-front wave functions, distribution amplitudes, form factors, valence structure functions and vector meson electroproduction phenomenology. The mass scale can be connected to the parameter in the QCD running coupling by matching the nonperturbative dynamics, as described by the light-front holographic approach to the perturbative QCD regime. The result is an effective coupling defined at all momenta. The matching of the high and low momentum-transfer regimes determines a scale Q₀ proportional to which sets the interface between perturbative and nonperturbative hadron dynamics. The use of Q₀ to resolve the factorization scale uncertainty for structure functions and distribution amplitudes, in combination with the scheme-independent Principle of Maximal Conformality (PMC) procedure for setting renormalization scales, can greatly improve the precision of perturbative QCD predictions.

The spin-charge-family theory, which is a kind of the Kaluza-Klein theories but with fermions carrying two kinds of spins (no charges), offers the explanation for all the assumptions of the standard model, with the origin of families, the higgs and the Yukawa couplings included. It offers the explanation also for other phenomena, like the origin of the dark matter and of the matter/antimatter asymmetry in the universe. It predicts the existence of the fourth family to the observed three, as well as several scalar fields with the weak and the hyper charge of the standard model higgs (, respectively), which determine the mass matrices of family members, offering an explanation, why the fourth family with the masses above 1 TeV contributes weakly to the gluon-fusion production of the observed higgs and to its decay into two photons, and predicting that the two photons events, observed at the LHC at ≈ 750 GeV, might be an indication for the existence of one of several scalars predicted by this theory.

We first review direct CP violation in the three-body baryonic B decays of with M_P = π, K and M_V = ρ, K^*. We then present our recent results of the direct CP violating asymmetries in the two-body Λ_b decays of Λ_b → pM_i as well as the three-body Λ_b → J/Ψ_pM_P. In particular, we emphasize that the large direct CP violating asymmetries in and are both around 20%, which are accessible to the b-hadron experiments.

The high-energy astrophysical neutrinos recently observed by IceCube may provide a new opportunity for new physics search in particle physics. In this talk, we discuss L_μ – L_τ gauge symmetry as an interesting example of new physics which is probed by the IceCube observatory.

The LHC experiments ATLAS and CMS have reported an excess in the diphoton spectrum at ∼750 GeV. At the same time the motivation for Supersymmetry (SUSY) remains unbowed. Consequently, we review briefly the proposals to explain this excess in SUSY, focusing on “pure” (N)MSSM solutions. We then review in more detail a proposal to realize this excess within the NMSSM. In this particular scenario a Higgs boson with mass around 750 GeV decays to two light pseudo-scalar Higgs bosons. Via mixing with the pion these pseudo-scalars decay into a pair of highly collimated photons, which are identified as one photon, thus resulting in the observed signal.

Form factors are important low-energy quantities and an accurate knowledge of these sheds light on the strong interactions. A variety of methods based on general principles have been developed to use information known in different energy regimes to constrain them in regions where experimental information needs to be tested precisely. Here we review our recent work on the electromagnetic ωπ form factor in a model-independent framework known as the method of unitarity bounds, partly motivated by the discre-pancies noted recently between the theoretical calculations of the form factor based on dispersion relations and certain experimental data measured from the decay ω → π⁰γ^*. We have applied a modified dispersive formalism, which uses as input the discontinuity of the ωπ form factor calculated by unitarity below the ωπ threshold and an integral constraint on the square of its modulus above this threshold. The latter constraint was obtained by exploiting unitarity and the positivity of the spectral function of a QCD correlator, computed on the spacelike axis by operator product expansion and perturbative QCD. An alternative constraint is obtained by using data available at higher energies for evaluating an integral of the modulus squared with a suitable weight function. From these conditions we derived upper and lower bounds on the modulus of the ωπ form factor in the region below the ωπ threshold. The results confirm the existence of a disagreement between dispersion theory and experimental data on the ωπ form factor around 0:6 GeV, including those from NA60 published in 2016.

I explain the cosmological consequence of the particle physics models with the Coleman–Weinberg (CW) type potential. Such particle physics models generally predict the small field inflation (SFI), but the SFI requires a very unnatural fine-tuning of the initial condi- tion. In this talk, I reviewed our proposal¹ to solve the fine-tuning problem dynamically by a trapping of the inflaton field due to the preheating before the SFI starts.

In the Standard Model, there is the single Higgs field, ϕ, which gives rise to constituent quark and lepton masses. The Yukawa coupling is a highly complex set of 3×3 matrices, resulting in many textures of quark and lepton masses.

In this talk, I present a model which transfers the complexity of the Yukawa coupling matrices to a family of Higgs fields, so that the Yukawa coupling itself becomes a simple interaction.

In the context of this Enriched Standard Model, we introduce a new r-symmetry in the extended SU(2)_L × U(1)_Y × U(1)_R model and show how the 125 GeV and 750 GeV resonances may be identified with H and H^′, the key members of the Higgs family, with H being in every way identifed with the SM Higgs. There are interesting consequences of their 2γ decay widths.

In light of the observation of a relatively large θ₁₃, one has to consider breaking the μ-τ symmetry properly which would otherwise result in a vanishing θ₁₃ (as well as θ₂₃ = π/4). Therefore, we investigate various symmetry-breaking patterns and accordingly identify those that are phenomenologically viable. Furthermore, the symmetry-breaking effects arising from some specific physics (e.g., the renormalization group equation running effect) are discussed as well.

Motivated by recent intensive experimental efforts on searching for neutrinoless double beta decays, we present a detailed quantitative analysis on the prospect of resolving neutrino mass ordering in the next generation ⁷⁶Ge-type experiments.

In view of recent observation of neutrino mixing angles and also the CP-phase, the model to predict the CP phase becomes more interesting. In 2000, we proposed the neutrino mass matrix that predicts the maximal CP violation and the 2-3 mixing angle. I revisit this model and explore this model further to investigate Majorana phases and the possible extension that allows the deviation of the CP phase and the 2-3 mixing from the maximal.

There is a wide class of models which give a dynamical description of the origin of avor in terms of spontaneous symmetry breaking of an underlying symmetry. Many of these models exhibit sum rules which relate on the one hand mixing angles and the Dirac CP phase with each other and/or on the other hand neutrino masses and Majorana phases with each other. We will briey sketch how this happens and discuss briey the impact of renormalization group corrections to the mass sum rules.

In a composite model of the weak bosons the p-wave bosons are studied. The state with the lowest mass is identified with the boson, which has been discovered at the LHC. Specific properties of the excited bosons are discussed, in particular their decays into weak bosons and photons. Recently a two-photon signal has been observed, which might come from the decay of a neutral heavy boson with a mass of about 0.75 TeV. This particle could be an excited weak tensor boson.

Composite Higgs models have the potential to provide a solution to the hierarchy problem and a dynamical explanation for the generation of the Higgs potential. They can be tested at the LHC as the new sector which underlies electroweak symmetry breaking must become strong in the TeV regime, which implies additional bound states beyond the Higgs. In this paper, we first discuss prospects and search strategies for top partners (and other quark partners) in the strongly coupled sector, which we study in an effective field theory setup. In the second part of the proceedings, we go beyond the effective field theory approach. We discuss potential UV embeddings for composite Higgs models which contain a Higgs as well as top partners. We show that in all of these models, additional pseudo-Nambu–Goldstone bosons beyond the Higgs are present. In particular, all of the models contain a pseudoscalar which couples to the Standard Model gauge fields through Wess–Zumino–Witten terms, providing a prime candidate for a di-boson (including a di-photon) resonance. The models also contain colored pNGBs which can be searched for at the LHC.

Four-dimensional Higgs field is identified with the extra-dimensional component of gauge potentials in the gauge-Higgs unifiation scenario. SO(5) × U(1) gauge-Higgs EW unification in the Randall–Sundrum warped space is successful at low energies. The Higgs field appears as an Aharonov–Bohm phase θ_H in the fifth dimension. Its mass is generated at the quantum level and is finite. The model yields almost the same phenomenology as the standard model for θ_H < 0.1, and predicts Z^′ bosons around 6–10 TeV with very broad widths. The scenario is generalized to SO(11) gauge-Higgs grand unification. Fermions are introduced in the spinor and vector representations of SO(11). Proton decay is naturally forbidden.

In this paper we consider some aspects of the Manohar–Wise extension of the SM with a colour-octet electroweak-doublet scalar applied to 2HDM. We present theoretical constraints on the parameters of this extension to both the SM and the 2HDM and discuss related phenomenology at LHC.

Vector boson scattering is (together with the production of multiple electroweak gauge bosons) the key process in the current run 2 of LHC to probe the microscopic nature of electroweak symmetry breaking. Deviations from the Standard Model are generically parameterized by higher-dimensional operators, however, there is a subtle issue of perturbative unitarity for such approaches for the process above. We discuss a parameter-free unitarization prescription to get physically meaningful predictions. In the second part, we construct simplified models for generic new resonances that can appear in vector boson scattering, with a special focus on the technicalities of tensor resonances.

The absence of the quadratic divergence in the Higgs sector of the Standard Model in the dimensional regularization is usually regarded to be an exceptional property of a specific regularization. To understand what is going on in the dimensional regularization, we illustrate how to reproduce the results of the dimensional regularization for the λϕ⁴ theory in the more conventional regularization such as the higher derivative regularization; the basic postulate involved is that the quadratically divergent induced mass, which is independent of the scale change of the physical mass, is kinematical and unphysical. This is consistent with the derivation of the Callan–Symanzik equation, which is a comparison of two theories with slightly different masses, for the λϕ⁴ theory without encountering the quadratic divergence. In this sense the dimensional regularization may be said to be generic in a bottom-up approach starting with a successful low energy theory. We also define a modified version of the mass independent renormalization for a scalar field which leads to the homogeneous renormalization group equation. Implications of the present analysis on the Standard Model at high energies and the presence or absence of SUSY at LHC energies are briey discussed.

By studying the t-J model for superconductivity, the Pati–Salam model and the Haplon model for particle unifications, we extract their common feature which is the spin-charge separation of fermions. This becomes a de-gauging process for charged fermions by considering them as bound states of a neutral fermion and charged or neutral bosons. We present a few examples including the weak-charge-spin separation for the leptons in the Standard Model. Some fundamental fermions can be obtained by continuing this de-gauging process for different kinds of charges. Finally the binding forces of the bound states might be provided by interactions related to spacetime symmetries such as supersymmetry.

With multi-spinor fields which behave as triple-tensor products of the Dirac spinors, the Standard Model is extended so as to embrace three families of ordinary quarks and leptons in the visible sector and an additional family of exotic quarks and leptons in the dark sector of our Universe. Apart from the gauge and Higgs fields of the Standard Model symmetry G, new gauge and Higgs fields of a symmetry isomorphic to G are postulated to exist in the dark sector. It is the bi-quadratic interaction between visible and dark Higgs fields that opens a main portal to the dark sector. Breakdowns of the visible and dark electroweak symmetries result in the Higgs boson with mass 125 GeV and a new boson which can be related to the diphoton excess around 750 GeV. Subsequent to a common inationary phase and a reheating period, the visible and dark sectors follow weakly-interacting paths of thermal histories. We propose scenarios for dark matter in which no dark nuclear reaction takes place. A candidate for the main component of the dark matter is a stable dark hadron with spin 3/2, and the upper limit of its mass is estimated to be 15.1 GeV/c².

I discuss possible connections between several scales in particle physics and cosmology, such the the electroweak, ination, dark energy and Planck scales. In particular, I discuss the physics of extra dimensions and low scale gravity that are motivated from the problem of mass hierarchy, providing an alternative to low energy supersymmetry. I describe their realization in type I string theory with D-branes and I present the main experimental predictions in particle accelerators and their implications in cosmology. I also show that low-mass-scale string compactifications, with a generic D-brane configuration that realizes the Standard Model by open strings, can explain the relatively broad peak in the diphoton invariant mass spectrum at 750 GeV recently reported by the ATLAS and CMS collaborations.

Next year we will celebrate 100 years of the cosmological term, Λ, in Einstein’s gravitational field equations, also 50 years since the cosmological constant problem was first formulated by Zeldovich, and almost about two decades of the observational evidence that a nonvanishing, positive, Λ-term could be the simplest phenomenological explanation for the observed acceleration of the Universe. This mixed state of affairs already shows that we do no currently understand the theoretical nature of Λ. In particular, we are still facing the crucial question whether Λ is truly a fundamental constant or a mildly evolving dynamical variable. At this point the matter should be settled once more empirically and, amazingly enough, the wealth of observational data at our disposal can presently shed true light on it. In this short review, I summarize the situation of some of these studies. It turns out that the Λ = const. hypothesis, despite being the simplest, may well not be the most favored one when we put it in hard-fought competition with specific dynamical models of the vacuum energy. Recently, it has been shown that the overall fit to the cosmological observables SNI_a+BAO+H(z)+LSS+BBN+CMB do favor the class of “running” vacuum models (RVM’s)— in which Λ = Λ(H) is a function of the Hubble rate — against the “concordance” ΛCDM model. The support is at an unprecedented level of ∼4σ and is backed up with Akaike and Bayesian criteria leading to compelling evidence in favor of the RVM option and other related dynamical vacuum models. I also address the implications of this framework on the possible time evolution of the fundamental constants of Nature.