Effects Of New Physics Research Articles

An imperative study of the angular observables in $$ {\Lambda}_b\to {\Lambda}_c^{+}\left(\to \Lambda {\pi}^{+}\right){\ell}^{-}{\overline{\nu}}_{\ell } $$ decay and probing the footprint of new physics

Abstract We study the four-fold angular distribution of the semileptonic $$ {\Lambda}_b\to {\Lambda}_c^{+}\left(\to \Lambda {\pi}^{+}\right){\ell}^{-}{\overline{\nu}}_{\ell } $$ Λ b → Λ c + → Λ π + ℓ − ν ¯ ℓ decay and find out analytical expressions for various asymmetric and angular observables in the standard model (SM) and the relevant new physics (NP) scenarios. Using the available inputs on the form factors from the lattice, we predict the values with uncertainties of all these observables in the SM. We have considered NP effects only in $$ b\to c{\tau}^{-}{\overline{\nu}}_{\tau } $$ b → c τ − ν ¯ τ transitions, and constrain the Wilson coefficients of the model-independent beyond the SM operators from the available data on B → D(*)ℓνℓ and $$ {\Lambda}_b\to {\Lambda}_c^{+}{\ell}^{-}{\overline{\nu}}_{\ell } $$ Λ b → Λ c + ℓ − ν ¯ ℓ decays. In this study, we focus on analysing the contributions to these decays in one- and two-operator scenarios. Furthermore, we test the new physics sensitivities (one or two-operator scenarios) of the different angular and asymmetric observables in $$ {\Lambda}_b\to {\Lambda}_c^{+}\left(\to \Lambda {\pi}^{+}\right){\tau}^{-}{\overline{\nu}}_{\tau } $$ Λ b → Λ c + → Λ π + τ − ν ¯ τ decays and discuss the phenomenology. We observe that it will be possible to distinguish the different NP effects from one another by measuring these observables.

Observation of γγ→ττ in proton–proton collisions and limits on the anomalous electromagnetic moments of the τ lepton

The production of a pair of τ leptons via photon-photon fusion,γγ→ττ, is observed for the first time in proton-proton collisions, with a significance of 5.3 standard deviations. This observation is based on a data set recorded with the CMS detector at the LHC at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 138 fb-1. Events with a pair of τ leptons produced via photon-photon fusion are selected by requiring them to be back-to-back in the azimuthal direction and to have a minimum number of charged hadrons associated with their production vertex. The τ leptons are reconstructed in their leptonic and hadronic decay modes. The measured fiducial cross section ofγγ→ττisσobsfid=12.4-3.1+3.8fb. Constraints are set on the contributions to the anomalous magnetic moment (aτ) and electric dipole moments (dτ) of the τ lepton originating from potential effects of new physics on theγττvertex:aτ=0.0009-0.0031+0.0032and|dτ|<2.9×10-17ecm(95% confidence level), consistent with the standard model.

One-loop contributions to WWZ from a seesaw variant with radiatively induced light neutrino masses

The experimental confirmation of neutrino mass and mixing disagrees with the picture of the Standard Model, and thus provides a good motivation to look for unknown physics. A seesaw variant in which neutrino masses are radiatively generated, with neutrinos characterized by Majorana fields and where a set of three hypothetical neutral heavy leptons are present, has been considered in the present work. We have calculated, estimated, and analyzed the contributions from virtual light and heavy neutrinos to the gauge vertex WWZ, in the context of a future electron-positron collider. We have found that contributions to both CP-even and CP-odd anomalous couplings are generated. Our estimations indicate that contributions as large as 10−3 can be achieved in both cases. This is particularly interesting for the CP-odd effects, which are expected to appear in the framework of the Standard Model since the three-loop order, thus being quite suppressed. By considering the expected sensitivity of the International Linear Collider to this gauge vertex, we conclude that these new-physics effects would be within its reach for e+e− collisions taking place at a center-of-mass energy of 800 GeV. Published by the American Physical Society 2024

Polarized and unpolarized off-shell decay above the threshold* *Supported by UNAM Posdoctoral Program (POSDOC), and the Sistema Nacional de Investigadores (Mexico)

An analysis of the off-shell decay width is presented for both unpolarized and polarized gauge bosons in the scenario with the most general vertex function, which is expressed in terms of two -even ( and ) and one -odd ( ) anomalous couplings. The SM contributions to the coupling up to the one-loop level are also included. Explicit analytic results for the unpolarized and polarized square amplitudes and the four-body phase space are presented, out of which several observable quantities can be obtained straightforwardly. Regarding numerical analysis, a cross-check was performed via , where our model was implemented with the aid of FeynRules. We then considered the most stringent bounds on anomalous complex couplings and analyzed the effects of the polarizations of the gauge bosons through the polarized decay width as well as left-right and forward-backward asymmetries, which were found to be sensitive to new-physics effects. Particular focus was put on the effects of the absorptive parts of the anomalous couplings, which have been largely overlooked up to now in LHC analyses. It was found that the studied observable quantities, particularly the left-right asymmetries, can be helpful to search for effects of -violation in the coupling and set bounds on the absorptive parts. For completeness, we also analyzed the case of unpolarized gauge bosons.

SMEFT chromomagnetic dipole operator contributions to tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t{{\\bar{t}}}$$\\end{document} production at approximate NNLO in QCD

We study higher-order QCD corrections for the production of a top–antitop quark pair (tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$t{{\\bar{t}}}$$\\end{document} production) at the Large Hadron Collider in the Standard Model Effective Field Theory. We consider effects of new physics parametrized by the top-quark chromomagnetic dipole operator. We calculate new physics contributions to the total cross section at approximate NNLO, with second-order soft-gluon corrections added to the complete NLO result, including uncertainties from scale dependence and from parton distributions. We also calculate new physics contributions at approximate NNLO for differential distributions in top-quark transverse momentum.

Bubble wall velocities with an extended fluid Ansatz

We compute the terminal bubble wall velocity during a cosmological phase transition by modelling non-equilibrium effects in the plasma with the so-called “extended fluid Ansatz”. A ϕ 6 operator is included in the Standard Model effective potential to mimic effects of new physics. Hydrodynamical heating of the plasma ahead of the bubble is taken into account. We find that the inclusion of higher order terms in the fluid Ansatz is typically relevant, and may even turn detonation solutions into deflagrations. Our results also corroborate recent findings in the literature that, for a Standard Model particle content in the plasma, only deflagration solutions are viable. However, we also show that this outcome may be altered in a theory with a different particle content.

Time-reversal asymmetries in * *Supported in part by the National Key Research and Development Program of China (2020YFC2201501) and the National Natural Science Foundation of China (NSFC) (12147103)

We study the decays of with . We examine the full angular distributions with polarized , where the T-odd observables are identified. We discuss the possible effects of new physics (NP) and find that the T-odd observables are sensitive to them as they vanish in the standard model. Special attention is given to the interference of (pseudo)scalar operators with (axial)vector operators in polarized , which are studied for the first time. Their effects are proportional to the lepton masses and therefore may evade the constraint from at the LHCb naturally. As is uncontaminated by the charmonia resonance, it provides a clean background to probe NP. In addition, we show that the experimental central value of in at the LHCb can be explained by the NP case, which couples to the right-handed quarks and leptons. The polarization fraction of at the LHCb is found to be consistent with zero regardless of the NP scenarios.

Single Transverse Spin Asymmetry as a New Probe of Standard-Model-Effective-Field-Theory Dipole Operators.

Electroweak dipole operators in the standard-model-effective-field theory (SMEFT) are important indirect probes of quantum effects of new physics beyond the standard model (SM), yet they remain poorly constrained by current experimental analyses for lack of interference with the SM amplitudes in constructing cross section observables. In this Letter, we point out that dipole operators flip fermion helicities and so are ideally studied through single transverse spin asymmetries. We illustrate this at a future electron-positron collider with transversely polarized beams, where such an effect exhibits as azimuthal cosϕ and sinϕ distributions which originate from the interference of the electron dipole operators with the SM and are linearly dependent on their Wilson coefficients. This new method can improve the current constraints on the electron dipole couplings by 1-2 orders of magnitude, without depending on other new physics operators, and can also simultaneously constrain both their real and imaginary parts, offering a new opportunity for probing potential CP-violating effects.

Optimal determination of new physics couplings: a comparative study

We study the determination of new physics (NP) parameters using the optimal observable technique (OOT) in situations where the standard model (SM) dominates over the NP effects, and when the NP dominates over the SM contribution, using the 2-Higgs doublet model as an illustrative example; for the case of SM domination we extend our results using an effective theory parameterization of NP effects. For the case of SM dominance we concentrate on tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} production in an e+e− collider, while for the case of NP dominance we consider both tt¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ t\\overline{t} $$\\end{document} production and pair production of charged scalars, also in an e+e− collider. We discuss the effects of the efficiency of background reduction, luminosity and beam polarization, and provide a comparison of the optimal uncertainties with those obtained using a standard χ2 analysis of (Monte Carlo generated) collider data.

Kaon theory: 50 years later

Abstract We summarize the status of the kaon theory 50 years after the seminal paper of Kobayashi and Maskawa [Prog. Theor. Phys. 49, 652 (1973)], who pointed out that six quarks are necessary to have CP violation in the Standard Model (SM) and presented a parametrization of a 3 × 3 unitary matrix that, after the discovery of the charm quark in 1974 and the b quark in 1977, dominated the field of flavor-changing processes. One of the main goals of flavor physics since then has been the determination of the four parameters of this matrix, which we will choose here to be |Vus|, |Vcb|, and the two angles of the unitarity triangle, β and γ, with |Vus| introduced by Cabibbo in 1963. I will summarize the recent strategy for determination of these parameters without new physics (NP) infection. It is based on the conjecture of the absence of relevant NP contributions to ΔF = 2 processes that indeed can be demonstrated by a negative rapid test: the |Vcb|–γ plot. This in turn allows one to obtain SM predictions for rare K and B decays that are the most precise to date. We present strategies for the explanation of the anticipated anomaly in the ratio ε′/ε and the observed anomalies in b → sμ+μ− transitions that are consistent with our ΔF = 2 conjecture. In particular, the absence of NP in the parameter εK still allows for significant NP effects in ε′/ε and in rare kaon decays, moreover, in a correlated manner. Similarly, the absence of NP in ΔMs combined with anomalies in b → sμ+μ− transitions hints at the presence of right-handed quark currents. We also discuss how the nature of neutrinos, Dirac vs. Majorana ones, can be probed in $K\rightarrow \pi \nu \bar{\nu }$ and $B\rightarrow K(K^{*})\nu \bar{\nu }$ decays. The present status of the ΔI = 1/2 rule and ε′/ε is summarized.

The new formulation of higgs effective field Theory

We present the explicit construction of the effective field theory (EFT) of standard model mass eigenstates. The EFT, which is invariant under U(1)e.m.× SU(3)c, is constructed based on the on-shell method and Young Tableau technique. This EFT serves as a new formulation of the Higgs EFT (HEFT), which can describe the infrared effects of new physics at the electroweak symmetry-breaking phase with greater conciseness. The current HEFT operator basis has a clear physical interpretation, making it more accessible for research in phenomenology. A complete list of HEFT operator bases for any-point vertices up to any dimension could be provided, and three- and four-point bases are provided as examples. Additionally, this framework realized as Mathematica program can be used to construct the EFT of any type of dark matter or particles with any spin.

Global constraints on non-standard neutrino interactions with quarks and electrons

We derive new constraints on effective four-fermion neutrino non-standard interactions with both quarks and electrons. This is done through the global analysis of neutrino oscillation data and measurements of coherent elastic neutrino-nucleus scattering (CEνNS) obtained with different nuclei. In doing so, we include not only the effects of new physics on neutrino propagation but also on the detection cross section in neutrino experiments which are sensitive to the new physics. We consider both vector and axial-vector neutral-current neutrino interactions and, for each case, we include simultaneously all allowed effective operators in flavour space. To this end, we use the most general parametrization for their Wilson coefficients under the assumption that their neutrino flavour structure is independent of the charged fermion participating in the interaction. The status of the LMA-D solution is assessed for the first time in the case of new interactions taking place simultaneously with up quarks, down quarks, and electrons. One of the main results of our work are the presently allowed regions for the effective combinations of non-standard neutrino couplings, relevant for long-baseline and atmospheric neutrino oscillation experiments.

Revealing new physics in {varvec{B}}^{0}_{s}rightarrow D_s^{mp } K^{pm } decays

The B^0_srightarrow D_s^{mp } K^{pm } system offers a determination of the Unitarity Triangle angle gamma . Intrigued by an LHCb analysis showing a surprisingly large result in tension with information on the Unitarity Triangle and other gamma measurements, we make a transparent study of the measured observables, confirming the LHCb picture. The corresponding gamma puzzle at the 3sigma level would require CP-violating contributions of New Physics, which should also manifest themselves in the corresponding decay branching ratios. Indeed, we find that the rates of the individual B^0_srightarrow D_s^{mp } K^{pm } channels show puzzling patterns, in accordance with similar decays, with tensions up to 4.8sigma , thereby making the situation much more exciting. We present a formalism to include New-Physics effects in a model-independent way and apply it to the data to constrain the corresponding parameters. Interestingly, new contributions of moderate size could accommodate the data. Utilising this formalism in the future high-precision B physics era may allow us to finally establish new sources of CP violation.

Kaon physics without new physics in varepsilon _K

Despite the observation of significant suppressions of brightarrow smu ^+mu ^- branching ratios no clear sign of New Physics (NP) has been identified in Delta F=2 observables Delta M_{d,s}, varepsilon _K and the mixing induced CP asymmetries S_{psi K_S} and S_{psi phi }. Assuming negligible NP contributions to these observables allows to determine CKM parameters without being involved in the tensions between inclusive and exclusive determinations of |V_{cb}| and |V_{ub}|. Furthermore this method avoids the impact of NP on the determination of these parameters present likely in global fits. Simultaneously it provides SM predictions for numerous rare K and B branching ratios that are most accurate to date. Analyzing this scenario within Z^prime models we point out, following the 2009 observations of Monika Blanke and ours of 2020, that despite the absence of NP contributions to varepsilon _K, significant NP contributions to K^+rightarrow pi ^+nu {bar{nu }}, K_{L}rightarrow pi ^0nu {bar{nu }}, K_Srightarrow mu ^+mu ^-, K_Lrightarrow pi ^0ell ^+ell ^-, varepsilon '/varepsilon and Delta M_K can be present. In the simplest scenario, this is guaranteed, as far as flavour changes are concerned, by a single non-vanishing imaginary left-handed Z^prime coupling g^L_{sd}. This scenario implies very stringent correlations between the Kaon observables considered by us. In particular, the identification of NP in any of these observables implies automatically NP contributions to the remaining ones under the assumption of non-vanishing flavour conserving Z^prime couplings to q{bar{q}}, nu {bar{nu }}, and mu ^+mu ^-. A characteristic feature of this scenario is a strict correlation between K^+rightarrow pi ^+nu {bar{nu }} and K_{L}rightarrow pi ^0nu {bar{nu }} branching ratios on a branch parallel to the Grossman-Nir bound. Moreover, Delta M_K is automatically suppressed as seems to be required by the results of the RBC-UKQCD lattice QCD collaboration. Furthermore, there is no NP contribution to K_Lrightarrow mu ^+mu ^- which otherwise would bound NP effects in K^+rightarrow pi ^+nu {bar{nu }}. Of particular interest are the correlations of K^+rightarrow pi ^+nu {bar{nu }} and K_{L}rightarrow pi ^0nu {bar{nu }} branching ratios and of Delta M_K with the ratio varepsilon '/varepsilon . We investigate the impact of renormalization group effects in the context of the SMEFT on this simple scenario.

Measurement of the very rare decay at the NA62 experiment

The decay, with a very precisely predicted branching ratio of less than 10−10, is among the best processes to reveal indirect effects of new physics. The NA62 experiment reports the branching ratio measurement BR() = ± 0.009| syst ) · 10−10 at 68% CL, based on the observation of 20 signal candidates with an expected background of 7.0 events from the total data sample collected at the CERN SPS during 2016-2018. This provides evidence for the very rare decay, observed with a significance of 3.4σ. This measurement is also used to set limits on BR(K + → π +X), where X is a new feebly interacting scalar or pseudo-scalar particle, foreseen in several new physics scenarios.

Kaon processes in general 2HDM

We discuss new physics (NP) contributions to kaon mixing parameter εK , direct CP violation parameter ε′/ε of K → ππ, and rare decays , and KL,S → μ+μ− in the context of general two Higgs doublet model. We focus on contributions of top quark related exotic couplings, and show that simultaneous presence of flavor conserving and flavor violating interactions can lead to large NP effects in kaon sector, while being consistent with the stringent constraints from B physics observables such as mixing, Bs → μ+μ−, and b → sγ. We stress on the importance of correlations between εK , and Bs → μ + μ − that can be exploited to distinguish the parameter space corresponding to a light (sub-TeV) or heavy (TeV) scale charged Higgs boson.

The stability and the lifetime of the scalar boson star

In this paper, we introduce the formalism to examine the impact of the dark scalar sector to the conformal and the electroweak symmetries breaking in the sense of formation of the scalar boson star (BS). The BS is presented by the local scalar field containing the Higgs boson field and the scalar dilaton field in the conformal field theory. We study in detail the modification of the Higgs quartic coupling away from its Standard Model (SM) value within the influence of the dark sector. We show that the repulsive self-interactions and the flatness degree in the dark scalar sector can prevent an instability and the destruction of the BS. We have estimated the rate of the deviation from the SM with production of leptonic pairs due to decays of dilatons and dark photons emerged because of the BS instability. The lifetime, the maximal mass and the density of the BS, the average minimal distance between the stars are estimated. The effects of new physics should be visible at the HL-LHC, FCC-hh accompanied by the current LHC and the cosmological data.

Parton distributions and new physics searches: the Drell–Yan forward–backward asymmetry as a case study

We discuss the sensitivity of theoretical predictions of observables used in searches for new physics to parton distributions (PDFs) at large momentum fraction x. Specifically, we consider the neutral-current Drell–Yan production of gauge bosons with invariant masses in the TeV range, for which the forward–backward asymmetry of charged leptons from the decay of the gauge boson in its rest frame is a traditional probe of new physics. We show that the qualitative behaviour of the asymmetry depends strongly on the assumptions made in determining the underlying PDFs. We discuss and compare the large-x behaviour of various different PDF sets, and find that they differ significantly. Consequently, the shape of the asymmetry observed at lower dilepton invariant masses, where all PDF sets are in reasonable agreement because of the presence of experimental constraints, is not necessarily reproduced at large masses where the PDFs are mostly unconstrained by data. It follows that the shape of the asymmetry at high masses may depend on assumptions made in the PDF parametrization, and thus deviations from the traditionally expected behaviour cannot be taken as a reliable indication of new physics. We demonstrate that forward–backward asymmetry measurements could help in constraining PDFs at large x and discuss the accuracy that would be required to disentangle the effects of new physics from uncertainties in the PDFs in this region.

Neutron-neutral particle mixing and its observable consequences

In this work, we explore the mixing between neutron ($n$) and elementary neutral particle ($\eta$), which violates both the baryon number ($\mathcal{B}$) and the lepton number ($\mathcal{L}$) by one unit but conserves their difference $(\mathcal{B}-\mathcal{L})$. Such mixing may give rise to non-trivial effects that are different from the Standard Model predictions. We organize our discussions based on two scenarios, roughly depending on whether an interference between oscillation and decay occurs, or whether the new-physics effects associated with the $n$-$\eta$ mixing contribute to the absorptive mixing amplitude. If an oscillation process is not accompanied by an interference between oscillation and decay, or the new-physics interactions do not contribute to the absorptive mixing amplitude, such a process can be classified as pure oscillation. Otherwise, it can be classified as impure oscillation. In the scenario of pure oscillation, CP-violation arising from the Majorana phase can manifest itself through the $n$-$\bar{n}$ oscillation process and may lead to observable effects. In the scenario of impure oscillation, we analyze the testable implications on the masses and lifetimes of the mass eigenstates formed as a result of the $n$-$\bar{n}$ oscillation mediated by $\eta$. In this scenario, we also suggest a unified interpretation of the neutron lifetime anomaly and the $n$-$\bar{n}$ oscillation measurements based on the $n$-$\eta$ mixing. In both scenarios, we present the lower bounds imposed by the experimental searches for $n$-$\bar{n}$ oscillations on the masses of the color multiplet bosons and point out that they could be within the reach of a direct detection at the LHC or future high-energy experiments.

Searching for new physics in the differential decay width of a Λb semi-leptonic decay

We propose to investigate the effects of new physics in the semi-leptonic sequential decay [Formula: see text]. 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.