Narrow Results

Possible manifestations of new physics in rare (exotic) decays of orthopositronium (o - Ps) are briefly reviewed. It is pointed out that models with infinite additional dimension(s) of Randall–Sundrum type predict disappearance of orthopositronium into additional dimension(s). The experimental signature of this effect is the invisible decay of orthopositronium. We point out that this process may occur at a rate within two or three orders of magnitude of the present experimental upper limit. We also propose a model with a light weakly interacting boson leading to o - Ps → invisible decays at the experimentally interesting rate. We discuss this in details and stress that the existence of invisible decay of orthopositronium in vacuum could explain the o - Ps decay rate puzzle. Thus, our result enhances the existing motivation and justifies efforts for a more sensitive search for o - Ps → invisible decay in a near future experiment.

New physics can show up in various well-known processes already studied in the Standard Model, in particular by modifying decay rates to some extent. In this work we examine leptonic decays of ϒ resonances of bottomonium below production, subsequent to a magnetic dipole radiative structural transition of the vector resonance yielding a pseudoscalar continuum state, searching for the existence of a light Higgs-like neutral boson that would imply a slight but experimentally measurable breaking of lepton universality.

The highlights and conflicts at the B factories are briefly reviewed. CP violation was established in 2001 in B⁰→J/ψK_S and related modes, which has now become a precision measurement of CP violation in mixing. However, the situation for the B⁰→π⁺π^- and charmless b→s modes, which also probe CP violation in the decay amplitude, are not quite settled yet. They could be hinting at the presence of both strong (CP conserving) and new physics (CP violating) phases. We critically assess the developments and discuss some related discrepancies and highlights, such as observation of direct CP violation, and make a projection towards the next few years.

We demonstrate the existence of model-independent one-to-one correspondence relations between different lepton flavor violating processes (LFV). Applying the criterion of naturalness, based on the idea of "custodial symmetry", we show that all the LFV processes, independently of specific mechanisms behind them, but with the same external leptons, have a priori comparable amplitudes modulo their kinematics and involved hadronic form factors.

Our previous analysis on the contributions of mirror matter admixtures in ordinary hadrons to K_L→γγ is extended to study the relevance of such contributions to the K_L→μ⁺μ^- rare decay. The mixing angle of the admixtures previously determined to describe the enhancement phenomenon in two-body non-leptonic decays of strange hadrons is used, along with recent results for the description of the strong and electromagnetic interaction parts of the transition amplitudes. We find that these admixtures give a significant contribution with a small SU(2) breaking of only 2.8%, we also find a value of ~ -17.9° for the η–η′ mixing angle consistent with some of its determinations in the literature and a preferred negative value around -16 for the local counterterm contribution χ₁+χ₂ consistent with the existence of a unique counterterm assuming lepton universality. We conclude that those mixings may be relevant in low energy physics and should not be ignored.

Experiments will soon start taking data at CERN's Large Hadron Collider (LHC) with high expectations for discovery of new physics phenomena. Indeed, the LHC's unprecedented center-of-mass energy will allow the experiments to probe an energy regime where the standard model is known to break down. Here, the experiments' capability to observe new resonances in various channels is reviewed.

In 2010, the Compact Muon Solenoid (CMS) experiment at LHC recorded over 45 pb^-1 of pp collision data at . The large collected datasets are of very high quality and have been used to commission and calibrate the CMS detector, with the achieved performance close to the TDR specifications. CMS has re-established all the major Standard Model processes in the 2010 Run and is entering new territory in searches for New Physics, with sensitivity already exceeding that at LEP and TeVatron.

Latest developments in leptogenesis are reviewed with a particular emphasis on the possibilities to test models of new physics, embedding the seesaw mechanism, by combining the requirement of successful leptogenesis with the information from low energy neutrino experiments. In particular, we discuss the role played by light and heavy flavor effects in the determination of the final asymmetry and the attractive features of the N₂-dominated scenario that is naturally realized within SO(10) models. We also discuss leptogenesis within discrete flavor symmetries models, supersymmetry and in the minimal two right-handed (RH) neutrino model.

Recently several developments have taken place in the lattice QCD calculations of hadronic factors in the case of and the mixings along with contribution of the long distance effects in the system. These have led some authors (Refs. 12 and 13) to point towards the possibility of New Physics (NP) in these systems to the tune of 20% or so. However, the present analysis, based on essentially NP free inputs and incorporating constraints of unitarity, shows that in case the NP effects are there in the parameters associated with these systems, e.g. sin 2β, V_td, ϵ_K, etc., these seem to be only at a few percent level.

The contributions of G′-boson predicted by the chiral color symmetry of quarks to the charge asymmetry in -production at the LHC and to the forward–backward asymmetry in -production at the Tevatron are calculated and analyzed in dependence on two free parameters of the model, the G′ mass m_G′ and mixing angle θ_G. The m_G′ - θ_G regions of 1 σ consistency with the CMS data on the cross-section and on the charge asymmetry are found and compared with those resulted from the CDF data on the cross-section and on the forward–backward asymmetry of -production at the Tevatron with account of the current SM predictions for .

Decays of B mesons into final states containing a τ lepton are sensitive to new charged current interactions that break lepton-flavor universality. These decays have been studied only at e⁺e^- colliders, where the low-background environment and well-known initial state make it possible to observe small signals with undetectable neutrinos. In particular, the large data samples of the B factories and recent advances in techniques for full-event reconstruction have led to evidence for the decay B⁺→τ⁺ ν_τ and unambiguous observation of the decays . These results exclude large regions of the parameter space for a variety of new physics models. Furthermore, the branching fraction for has been measured to be higher than the Standard Model expectation by more than three standard deviations, making this an interesting topic for further research. This paper reviews the theoretical and experimental status of this topic, summarizing the results at this time and outlining the path for further improvements.

The contributions of $G^{\prime }$-boson predicted by the chiral color symmetry of quarks to the differential dijet cross-sections in pp-collisions at the large hadron collider (LHC) are calculated and analyzed in dependence on two free parameters of the model, the $G^{\prime }$ mass $m_{G^{\prime }}$ and mixing angle ${𝜃}_G$. The exclusion and consistency $m_{G^{\prime }}-{𝜃}_G$ regions imposed by the ATLAS and CMS data on dijet cross-sections are found. Using the CT10 (MSTW2008) parton distribution function (PDF) set we show that the $G^{\prime }$-boson for ${𝜃}_G=45^{\circ }$, i.e. the axigluon, with the masses $m_{G^{\prime }}<2.3(2.6)$ TeV and $m_{G^{\prime }}<3.35(3.25)$ TeV is excluded at the probability level of 95% by the ATLAS and CMS dijet data, respectively. For the other values of ${𝜃}_G$ the exclusion limits are more stringent. The $m_{G^{\prime }}-{𝜃}_G$ regions consistent with these data at CL = 68% and CL = 90% are also found.

Assuming that the corrections to relevant Wilson coefficients from new physics (NP) contain the possible CP phases, we analyze the constraints on the NP corrections from the updated experimental data on rare B decays from LHCb, BABAR, and BELLE, etc. systematically. Through global fit among the theoretical evaluations and corresponding experimental observations, we find that the possible CP phases of the corrections to relevant Wilson coefficients from NP affect the allowed parameter space obviously.

We propose two different and complementary observables for singling out possible signals of physics beyond the Standard Model (SM) in the semi-leptonic decays ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c\ell {\bar{\nu }}_{\ell }$, both with the $\tau$ lepton and with a light lepton. The two observables are the partial decay width and a T-odd asymmetry, whose respective sensitivities to scalar and/or pseudo-scalar coupling are calculated as functions of the parameters characterizing new physics (NP). Two different form factors are used. Three particular cases are discussed and analyzed in detail.

We investigate the nonstandard neutrino interactions (NSI) in the rare decays of $B_c^{+}$ mesons involving neutrinos in the final state. It is suggested that the interference between Standard Model and nonstandard interaction can provide sizeable contribution. We calculate the limits on NSI free parameters (${𝜖}_{\tau \tau }^{uL}$, ${𝜖}_{\tau \tau }^{dL}$) and compare them with experimental data.

Construction of future Muon Collider (or dedicated $\mu$-ring) tangential to the energy frontier $hh$ colliders will give opportunity to realize $\mu p$ and $\mu A$ collisions at multi-TeV center-of-mass energies with sufficiently high luminosities. Obviously, such colliders will essentially enlarge the physics search potential of corresponding muon and hadron colliders for both the SM (especially for clarifying QCD basics and confinement hypothesis) and BSM phenomena. In addition, they will provide parton distribution functions for adequate interpretation of energy frontier $hh$ colliders’ and cosmic ray experiments data. This paper is devoted to review of main parameters of $\mu h$ colliders proposed until now.

We propose to investigate the effects of new physics in the semi-leptonic sequential decay ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c(\to \mathrm{\Lambda }\pi )\tau {\bar{\nu }}_{\tau }$. First, we write the general, model-independent, non-covariant expression of the differential decay width of the process. Then, we calculate that observable according to three different types of new physics interactions, which might explain the tension of data with the Standard Model predictions. We find that some coefficients of the differential decay width are sensitive to the kind of interaction that is assumed. The measurements that we suggest seem to be feasible.

We implement the ${\chi }^2$ fit for $R(K^{(\ast )})$ with possible tree-level new physics in a model-independent parametrization. Relevant Wilson coefficients are decomposed into the new physics scale, its power, and the fermionic couplings. Constraints from the branching ratio of $B_s\to {\mu }^{+}{\mu }^{-}$ can be naturally incorporated with the scheme. For a reasonable set of the parameter ranges it is found that the new physics is less than $\sim 5\mathrm{\text{TeV}}$. Some new physics models including the leptoquark, $Z^{\prime }$, etc. can be embraced within our framework. We give comments on new LHCb data which are close to the standard model predictions.

Virtual effects induced by new physics in rare Z decays are reviewed. Since the expected sensitivity of the giga-Z linear collider is of the order of 10^-8, we emphasize the importance of any new physics effect that gives a prediction above this limit. It is also pointed out that an improvement on the known experimental constraints on rare Z decays will provide us with a critical test of the validity of the standard model at the loop level.

In this work, we examine the possible existence of new physics beyond the standard model which could modify the branching fractions of the leptonic (mainly tauonic) decays of bottomonium vector resonances below the threshold. The decay width is factorized as the product of two pieces: (a) the probability of an intermediate pseudoscalar color-singlet state (coupling to the dominant Fock state of the Upsilon via a magnetic dipole transition) and a soft (undetected) photon; (b) the annihilation width of the pair into two leptons, mediated by a non-standard CP-odd Higgs boson of mass about 10 GeV, introducing a quadratic dependence on the lepton mass in the partial width. The process would be unwittingly ascribed to the ϒ leptonic channel thereby (slightly) breaking lepton universality. A possible mixing of the pseudoscalar Higgs and bottomonium resonances is also considered. Finally, several experimental signatures to check out the validity of the conjecture are discussed.