Measuring hidden Higgs and strongly-interacting Higgs scenarios

Higgs couplings can be affected by physics beyond the Standard Model. We study modifications through interactions with a hidden sector and in specific composite Higgs models accessible at the LHC. Both scenarios give rise to congruent patterns of universal, or partially universal, shifts. In addition, Higgs decays to the hidden sector may lead to invisible decay modes which we also exploit. Experimental bounds on such potential modifications will measure the concordance of an observed Higgs boson with the Standard Model.     

Minimal flavour violation and beyond

The presence of new sources of massive boosted particles associated with processes probing the electroweak scale is a logical possibility that forms a solid window towards physics beyond the standard model. Such objects when decaying into hadronic final states can easily blend with the cornucopia of jets interpolated from essentially massless fundamental QCD states. We review jet observables and algorithms that can contribute to the identification of highly boosted heavy jets and the possible searches that can make use of such substructure information. We also review previous studies by CDF of boosted massive jets and measurement of jet shape observables.     

Geometrical CP violation from non-renormalisable scalar potentials

We consider in detail the non-renormalisable scalar potential of three Higgs doublets transforming as an irreducible triplet of Δ(27)$\mathrm{\Delta }(27)$ or Δ(54)$\mathrm{\Delta }(54)$. We start from a renormalisable potential that spontaneously leads to a vacuum with CP-violating phases independent of arbitrary parameters – geometrical CP violation. Then we analyse to arbitrarily high order non-renormalisable terms that are consistent with the symmetry and we demonstrate that inclusion of non-renormalisable terms in the potential can preserve the geometrical CP-violating vacuum.     

漫谈希格斯粒子

希格斯玻色子发现于2012年,是粒子物理学研究中的一件划时代的大事。它在粒子物理的“标准模型”中起关键性作用,通过神秘的对称性破缺机制给基本粒子带来质量,和高深莫测的量子真空息息相关,也被认为在宇宙演化的极早期起重要作用。在希格斯玻色子发现十周年之际,文章将从科普视角出发,描绘希格斯玻色子的理论背景、粒子特性、实验探测、研究现状和展望,揭开希格斯玻色子的神秘面纱,理解它的过去、现在和未来。     

Physics beyond Standard Model: Working group 3 report

This is a summary of the beyond the Standard Model (including model building) working group of the WHEPP-X workshop held at Chennai from January 3 to 15, 2008. Participants: Neelima Agarwal, S K Agarwalla, C S Aulakh, A Belyaev, S S Biswal, B Bhattacharjee, G Bhattacharyya, L Calibbi, D Choudhury, E J Chun, D Das, A De Roeck, N G Deshpande, E Dudas, A Giri, D Grellshceid, R Godbole, S Goswami, M Guchait, M Hirsch, R Kaul, B Kodrani, M C Kumar, A Kundu, Y Mambrini, P Mathews, B Mellado, R Mohanta, S Mohanty, A Nyffeler, S Pakvasa, M K Parida, M Passera, C Petridou, S Poddar, P Poulose, A Rajaraman, G Rajasekaran, V Ravindran, Kumar Rao, D P Roy, Probir Roy, K A Saheb, V H Satheeshkumar, T Schwetz, A Tripathi, R Vaidya and S Vempati     

Neutrino masses and mixings: a theoretical perspective

We briefly review the recent activity on neutrino masses and mixings which was prompted by the confirmation of neutrino oscillations by the Superkamiokande experiment.     

Precision tests of the standard model,the Higgs,and new physics

We present a concise review of the status of the standard model and of the search for new physics.     

Radiatively induced flavour violation in the general two-Higgs doublet model with Yukawa alignment

The most general two-Higgs doublet model contains new sources of flavour violation that are usually in conflict with the experimental constraints. One possibility to suppress the exotic contribution to the flavour changing neutral currents consists on imposing the alignment of the Yukawa couplings. This condition presumably holds at a high-energy scale and is spoiled by the radiative corrections. We compute in this Letter the size of the radiatively induced flavour violating Higgs couplings at the electroweak scale. These also yield the absolute lower bound on the size of the exotic contributions to the flavour changing neutral currents in any two-Higgs doublet model, barring cancellations and the existence of discrete symmetries. We show that these contributions are well below the experimental bounds in large regions of the parameter space.     

希格斯玻色子发现简史

希格斯玻色子于2012年的发现是粒子物理发展史上的一座里程碑。它为标准模型补上了最后一块拼图,希格斯机制的提出者们也因此获得了2013年的诺贝尔物理学奖。在希格斯玻色子发现十周年之际,文章将带领读者简短回顾希格斯玻色子从提出到发现的近半个世纪的历史。     

Constraining new physics in with reparametrization invariance and QCD factorization

Usually, B⁰→π⁺π⁻ decays are expressed in terms of weak amplitudes explicitly dependent on the CKM weak phase α or γ. In this Letter, we show that the weak amplitudes can be rewritten such that a manifest dependence on β emerges instead. Based on this, we constrain new-physics contributions to the CP-violating phase _d in mixing. Further, we apply reparametrization invariance and use QCD factorization predictions to investigate the bounds on an additional new-physics amplitude in B⁰→π⁺π⁻.     

Heavy flavour physics and CP violation at LHCb: A ten-year review

Heavy flavour physics provides excellent opportunities to indirectly search for new physics at very high energy scales and to study hadron properties for deep understanding of the strong interaction. The LHCb experiment has been playing a leading role in the study of heavy flavour physics since the start of the LHC operations about ten years ago, and made a range of high-precision measurements and unexpected discoveries, which may have far-reaching implications on the field of particle physics. This review highlights a selection of the most influential physics results on CP violation, rare decays, and heavy flavour production and spectroscopy obtained by LHCb using the data collected during the first two operation periods of the LHC. The upgrade plan of LHCb and the physics prospects are also briefly discussed.     

Search for a lighter Higgs boson in the Next-to-Minimal Supersymmetric Standard Model

Following the discovery of the Higgs boson with a mass of approximately 125 Ge V at the LHC, many studies have been performed from both the theoretical and experimental viewpoints to search for a new Higgs Boson that is lighter than 125 Ge V. We explore the possibility of constraining a lighter neutral scalar Higgs boson h_1 and a lighter pseudo-scalar Higgs boson a_1 in the Next-to-Minimal Supersymmetric Standard Model by restricting the next-to-lightest scalar Higgs boson h_2 to be the one observed at the LHC after applying the phenomenological constraints and those from experimental measurements. Such lighter particles are not yet completely excluded by the latest results of the search for a lighter Higgs boson in the diphoton decay channel from LHC data. Our results show that some new constraints on the Next-to-Minimal Supersymmetric Standard Model could be obtained for a lighter scalar Higgs boson at the LHC if such a search is performed by experimental collaborations and more data. The potentials of discovery for other interesting decay channels of such a lighter neutral scalar or pseudo-scalar particle are also discussed.     

Strongly first order phase transitions near an enhanced discrete symmetry point

We propose a group theoretic condition which may be applied to extensions of the Standard Model in order to locate regions of parameter space in which the electroweak phase transition is strongly first order, such that electroweak baryogenesis may be a viable mechanism for generating the baryon asymmetry of the universe. Specifically, we demonstrate that the viable corners of parameter space may be identified by their proximity to an enhanced discrete symmetry point. At this point, the global symmetry group of the theory is extended by a discrete group under which the scalar sector is non-trivially charged, and the discrete symmetry is spontaneously broken such that the discrete symmetry relates degenerate electroweak preserving and breaking vacua. This idea is used to investigate several specific models of the electroweak symmetry breaking sector. The phase transitions identified through this method suggest implications for other relics such as dark matter and gravitational waves.     

Two Higgs bi-doublet left-right model with spontaneous P and CP violation

A left-right symmetric model with two Higgs bi-doublet is shown to be a consistent model for both spontaneous P and CP violation. The flavor changing neutral currents can be suppressed by the mechanism of approximate global U(1) family symmetry. The constraints from neural K meson mass difference Δm _K are calculated and it is demonstrated that a right-handed gauge boson W ₂ contribution in box-diagrams with mass well below 1 TeV is allowed due to a cancelation caused by a light-charged Higgs boson with a mass range of 150–300 GeV. The W ₂ contribution to ε _K can be suppressed from an appropriate choice of additional CP phases appearing in the right-handed Cabbibo-Kobayashi-Maskawa matrix. The model is also found to be fully consistent with B ⁰ mass difference Δm _B and the mixing induced CP violation sin2β _{J/ Ψ}, which is usually difficult for the model with only one Higgs bi-doublet. The new physics beyond the standard model can be directly searched at the colliders LHC and ILC. Supported by the National Natural Science Foundation of China (NSFC) (Grant Nos. 10475105 and 10491306) and the Key Project of Chinese Academy of Sciences (CAS)     

The bases of effective field theories

With reference to the equivalence theorem, we discuss the selection of basis operators for effective field theories in general. The equivalence relation can be used to partition operators into equivalence classes, from which inequivalent basis operators are selected. These classes can also be identified as containing Potential-Tree-Generated (PTG) operators, Loop-Generated (LG) operators, or both, independently of the specific dynamics of the underlying extended models, so long as it is perturbatively decoupling. For an equivalence class containing both, we argue that the basis operator should be chosen from among the PTG operators, because they may have the largest coefficients. We apply this classification scheme to dimension-six operators in an illustrative Yukawa model as well in the Standard Model (SM). We show that the basis chosen by Grzadkowski et al. [5] for the SM satisfies this criterion. In this light, we also revisit and verify our earlier result [6] that the dimension-six corrections to the triple-gauge-boson couplings only arise from LG operators, so the magnitude of the coefficients should only be a few parts per thousand of the SM gauge coupling if BSM dynamics respects decoupling. The same is true of the quartic-gauge-boson couplings.     

Prospects for Higgs boson searches at the Large Hadron Collider

These proceedings summarize the sensitivity for the CMS and ATLAS experiments at the LHC to discover a Standard Model Higgs boson with relatively low integrated luminosity per experiment. The most relevant discovery modes are dealt with. A brief discussion on the expected performance from these experiments in searches for one or more of the Higgs bosons from the minimal version of the supersymmetric theories is also included.      

Family symmetries and alignment in multi-Higgs doublet models

The exact alignment of the Yukawa structures on multi-Higgs doublet models provides cancellation of tree-level flavour changing couplings of neutral scalar fields. We show that family symmetries can provide a suitable justification for the Yukawa alignment.     

Muon g-2 discrepancy:new physics or a relatively light Higgs?

After a brief review of the muon g-2 status,we discuss hypothetical errors in the Standard Model prediction that might explain the present discrepancy with the experimental value.None of them seems likely.In particular,a hypothetical increase of the hadroproduction cross section in low-energy e+e-collisions could bridge the muon g-2 discrepancy,but it is shown to be unlikely in view of current experimental error estimates.If,nonetheless,this turns out to be the explanation of the discrepancy,then the 95% CL upper bound on the Higgs boson mass is reduced to about 135 GeV which,in conjunction with the experimental 114.4 GeV 95%CL lower bound,leaves a narrow window for the mass of this fundamental particle.     

Higgs-boson couplings beyond the Standard Model

The implications for Higgs decays of potential new physics beyond the Standard Model (BSM) are considered in the context of effective field theory, assuming perturbative decoupling. Using existing data to restrict which dimension-six operators can arise, it is shown that, given the existing experimental constraints, only a small number of operators can affect the decays of the Higgs: those that may be potentially-tree-generated (PTG) and modify the Higgs–fermion couplings, or those that may be loop-generated (LG) that modify the Higgs couplings to γγ, Zγ and GG  . Implications for specific branching ratios are given in terms of the coefficients of various dimension-six operators. In such a scenario, the ratios Γ(H→WW^?)/Γ(H→ZZ^?)$\Gamma (H\to W{W}^{?})/\Gamma (H\to Z{Z}^{?})$ and Γ(H→W?ν)/Γ(H→Z??)$\Gamma (H\to W?\nu )/\Gamma (H\to Z??)$ equal to their Standard Model values to an accuracy of O(1%)$O(1\text{\%})$ or less.