4 pages, 2 figures; prepared for the 12th international conference on Topics in Astroparticle and Underground Physics, TAUP2011. v2: matches accepted version
A poorly constrained parameter in the Standard Model of Cosmology is the lepton asymmetry l = \sum_f l_f=\sum_f(n_f+n_{ν_f})/s. Each flavour asymmetry l_f with f=e, μ, τ is the sum of the net particle density of the charged leptons n_f and their corresponding neutrinos, normalized with the entropy density s. Constraints on l_f \leq O(0.1) from BBN and CMB allow for lepton flavour asymmetries orders of magnitudes larger then the baryon asymmetry b ~ 10^{-10}. In this article we show how such large lepton (flavour) asymmetries influence the early universe, in particular the freeze out of WIMPs and the cosmic QCD transition.
The interpretation of high-precision lepton-nucleon scattering experiments requires the knowledge of higher-order radiative corrections. We present a calculation of the cross section for unpolarized lepton-proton scattering including leptonic radiative corrections up to second order, including one- and two-loop corrections, radiation of one and two photons and one-loop corrections for one-photon radiation. Numerical results are given for the planned P2 experiment at the MESA facility in Mainz, and some results are also discussed for Qweak and the suggested MUSE experiment.
We study the energy correlation of charged leptons produced in the decay of a heavy Higgs particle $H\to t\bar t\to bl^+ν_l\bar bl^-\barν_l$ and $H\to W^+W^-\to l^+ν_ll^-\barν_l.$ The possible influence of $CP$--violation in the $Ht\bar t$ and $HW^+W^-$ vertices on the energy spectrum of the secondary leptons is analyzed. The energy distribution of the charged leptons in the decay $H\to W^+W^-\to l^+ν_ll^-\barν_l$ is sensitive to the $CP$--parity of the Higgs particle and yields a simple criterion for distinguishing scalar Higgs from pseudoscalar Higgs.
The masses of quarks and leptons in units of $m_t$ are expressed in powers of $σ=\sqrt{m_c/m_t}$. The regularities found suggest specific mass matrices. They reproduce all masses and mixings in striking agreement with observation. A 90 degree relative phase angle between the off-diagonal elements of up and down quark matrices leads to a maximum magnitude for CP-violation and, for the phase angle $γ$ of the unitary triangle, to $γ\simeq 90^o$.
We extend previous computations of the second order QCD corrections to semileptonic b \to c inclusive transitions, to the case where the charged lepton in the final state is massive. This allows accurate description of b \to c τ\bar ν_τdecays. We review techniques used in the computation of O(α_s^2) corrections to inclusive semileptonic b \to c transitions and present extensive numerical studies of O(α_s^2) QCD corrections to b \to c l \bar ν_l decays, for l =e, τ.
It can be expected from the result for the atmospheric neutrino by the SUPERKAMIOKANDE and the CHOOZ result that the the lepton-flavor violating (LFV) interaction between the second and third generations exits at the high energy scale. This leads to a non-vanishing LFV left-handed slepton mass between the second and third generations, induced by the radiative correction, in the minimal supergravity scenario. In this article, assuming that the supersymmetric standard model with the right-handed neutrinos explains the atmospheric neutrino result, we show that the reach of the LFV slepton product…
This paper reports the evaluation of the tenth-order QED contribution to the lepton g-2 from the gauge-invariant set of 2072 Feynman diagrams, called Set IV, which are obtained by inserting a second-order lepton vacuum-polarization loop into 518 eighth-order vertex diagrams of four-photon exchange type. The numerical evaluation is carried out by the adaptive-iterative Monte-Carlo integration routine vegas using the fortran codes written by the automatic code-generating algorithm gencodeN. Some of the numerical results are confirmed by comparison with the values of corresponding integrals that …
A simple breaking of the subnuclear democracy of the quarks leads to a mixing between the second and the third family, in agrement with observation. Introducing the mixing between the first and the second family, one finds an interesting pattern of maximal CP--violation as well as a complete determination of the elements of the CKM matrix and of the unitarity triangle.
Motivated by the recent Xenon1T result, we study a leptophilic flavour-dependent anomaly-free axion-like particle (ALP) and its effects on charged-lepton flavour violation (CLFV). We present two representative models. The first one considers that the ALP origins from the flavon that generates the charged-lepton masses. The second model assumes a larger flavour symmetry such that more general mixings in the charged-lepton are possible, while maintaining flavour-dependent ALP couplings. We find that a keV ALP explaining the Xenon1T result is still viable for lepton flavour violation and stellar …
Constrained flavor violation is a recent proposal for predicting the down-quark Yukawa matrix in terms of those for up quarks and charged leptons. We study the viability of CFV with respect to its predictions for the lepton mass ratios, showing that this remains a challenge, and suggest some possible means for improving this shortcoming. We then extend CFV to include neutrinos, and show that it leads to interesting predictions for hierachical heavy neutrinos, and leptogenesis dominated by decays of the second heaviest one ("N2 leptogenesis"), as well as the possibility of low-scale leptoquark-…
The lepton flavour asymmetries of the Universe are observationally almost unconstrained before the onset of neutrino oscillations. We calculate the cosmic trajectory during the cosmic QCD epoch in the presence of large lepton flavour asymmetries. By including QCD thermodynamic quantities derived from functional QCD methods in our calculation our work reveals for the first time the possibility of a first-order cosmic QCD transition. We specify the required values of the lepton flavour asymmetries for which a first-order transition occurs for a number of different benchmark scenarios.
We obtain analytic expressions for the energy and polar-angle double differential distributions of a secondary lepton l+ (l-) arising from the decay of t (tbar) in e+e- -> t tbar with an anomalous tbW decay vertex. We also obtain analytic expressions for the various differential cross sections with the lepton energy integrated over. In this case, we find that the angular distributions of the secondary lepton do not depend on the anomalous coupling in the decay, regardless of possible anomalous couplings occurring in the production amplitude for e+e- -> t tbar. Our study includes the effect of …
This paper reports the tenth-order QED contribution to the g-2 of electron and muon from two gauge-invariant sets, Set I(g) and Set I(h). In the case of electron g-2 Set I(g) consists of 9 Feynman diagrams which have a 4th-order vacuum-polarization loop containing another 4th-order vacuum-polarization loop. Set I(h) consists of 30 Feynman diagrams which have a proper 6th-order vacuum-polarization loop containing a second-order vacuum-polarization loop. The results of numerical integration, including mass-dependent terms containing one closed loop of muon, are 0.028 597 (4) (alpha/pi)^5 for Set…
Hypothetical particles called heavy neutral leptons (HNLs) can be produced in large quantities in the cores of supernovae during the first seconds of the explosion. These particles then decay, producing secondary energetic neutrinos that can be detected by neutrino detectors. In this paper, I identify a region of the HNL parameter space that could be tested using this method, assuming a supernova explosion at distances from 0.2 to 10 kpc. The range of HNLs masses $m_N \sim 160-700$ MeV and lifetimes of $τ_N \gtrsim 0.02$ seconds can be probed using the Hyper-Kamiokande neutrino detector. This …
We propose a radiatively induced quark and lepton mass model in the first and second generation with extra $U(1)$ gauge symmetry and vector-like fermions. Then we analyze the allowed regions which simultaneously satisfy the FCNCs for the quark sector, LFVs including $μ-e$ conversion, the quark mass and mixing, and the lepton mass and mixing. Also we estimate the typical value for the $(g-2)_μ$ in our model.
Recent results on second order quantum corrections to semileptonic decays of b quarks and positronium spectroscopy are reviewed. Similarities between calculations in these seemingly different problems are demonstrated. Technical aspects of solving systems of recurrence relations, and application of dimensional regularization to bound states are explained.
We show that the mass matrix of electrically neutral gauge bosons in the recently proposed model based on SU(3)_C X SU(3)_L X U(1)_X group with three lepton singlets [1] has two exact eigenvalues: a zero corresponding the photon mass and the second one equaling the mass of the imaginary component A_5μ}. Hence the neutral non-Hermitian gauge boson X^0_μ( defined as \sqrt{2} X^0_μ= A'_ 4μ- i A_5μ) is properly determined. With extra vacuum expectation value of the Higgs field n_2, there are mixings among the Standard Model W boson and the extra charged gauge boson Y carrying lepton number 2 (bile…
We suppose that the observed neutrino masses can be parametrised by a lepton number violating dimension-five operator, and calculate the mixing of double insertions of this operator into lepton flavour changing dimension-six operators of the standard model effective theory. This allows to predict the log-enhanced, but $m_ν^2$-suppressed lepton flavour violation that is generic to high-scale Majorana neutrino mass models. We also consider the Two Higgs Doublet Model, where the second Higgs allows the construction of three additional dimension-five operators, and evaluate the corresponding anoma…
We present an $S_4$ flavor model to unify quarks and leptons in the framework of the SU(5) GUT. Three generations of $\bar 5$-plets in SU(5) are assigned $3_1$ of $S_4$ while the first and the second generations of 10-plets in SU(5) are assigned to be 2 of $S_4$, and the third generation of 10-plet is to be $1_1$ of $S_4$. Right-handed neutrinos are also assigned 2 for the first and second generations and $1_1$ for the third generation, respectively. Taking vacuum alignments of relevant gauge singlet scalars, we predict the quark mixing as well as the tri-bimaximal mixing of neutrino flavors. …
In supersymmetric extensions of the Standard Model, the Yukawa and/or mass terms of the heavy neutrinos can generate lepton flavour violating slepton mass terms. These new supersymmetric sources of lepton flavour violation may both enhance the rates of charged lepton flavour violating processes, l_a -> l_b y, and generate distinct final states, like l_b l_a + jets + missing E_T, at future colliders. First, we discuss the sensitivity of future e^+e^- colliders to the SLFV independently of the lepton flavour violating mechanism. Second, we study lepton flavour violating slepton pair production a…
We have presented a $S_4$ flavor model to unify quarks and leptons in the framework of the SU(5) GUT. Three generations of $\bar5$-plets in SU(5) are assigned $3_1$ of $S_4$ while the first and the second generations of 10-plets in SU(5) are assigned to be 2 of $S_4$, and the third generation of 10-plet is to be $1_1$ of $S_4$. The right-handed neutrinos are also assigned 2 for the first and second generations and $1_1$ for the third generation, respectively. Taking vacuum alignments of relevant gauge singlet scalars, we predict the quark mixing as well as the tri-bimaximal mixing of neutrino …
This note reviews recent theoretical developments in the study of charged lepton flavour violation. The first part illustrates the status of precise next-to-leading order quantum electrodynamics calculations for the background of charged lepton flavour-violating processes, with a focus on the muonic "rare" and "radiative" decays. Phenomenological implications of these computations and their impact on present and future experiments will be discussed. The second part describes the recent progress in the effective field theory interpretation of charged lepton-flavour violating observables in conn…
We study phenomenological consequences of the strong first-order electroweak phase transition in an extension of the standard model with an inert doublet and vector-like leptons motivated by the muon $g-2$ anomaly and dark matter. We find that a condition for the strong first-order electroweak phase transition inevitably induces a large logarithmic enhancement in $Z$ boson decays, which relegates the explanation of the anomalous muon $g-2$ at below 2$σ$ level. Our analysis shows that future lepton collider experiments, especially the Giga-$Z$ at the International Linear Collider and Tera-$Z$ a…
Flavor Democracy Hypothesis favors existence of iso-singlet quarks and vector-like charged leptons. Their observation at future colliders could shed light on the nature of mass and mixing patterns of known leptons and quarks, as well as Higgs boson itself. Vector-like quarks are extensively searched by ATLAS and CMS collaborations. Unfortunately, this is not the case for vector-like leptons, while they have actually similar status from phenomenology viewpoint. We argue that vector-like charged leptons should be included into the new physics search programs of future energy frontier colliders. …
A beam dump experiment can be seamlessly added to the {proposed} International Linear Collider (ILC) program because the high energy electron beam should be dumped after the collision point. The ILC beam dump experiment will provide an excellent opportunity to search for new long-lived particles. Since many of them can be produced by a rare decay of standard model particles, we evaluate spectra of the mesons and $τ$ lepton at the decay based on the PHITS and PYTHIA8 simulations. As a motivated physics case, we study the projected sensitivity of heavy neutral leptons at the ILC beam dump experi…
Assuming that the leptonic mixing matrix is given in first approximation by the tribimaximal form we deduce some consequences with regard to the finite symmetries that may be applied in the minimal lepton sector of the electroweak theory.
We discuss QED radiative corrections at first and second order for the parity violating asymmetry $A_\text{PV}$ in elastic electron proton scattering. A measurement of $A_\text{PV}$ is planned at low energies and with high precision by the forthcoming P2 experiment at the new MESA facility in Mainz. Bremsstrahlung leads to a shift of the momentum transfer $Q^2$ which affects the determination of the weak charge of the proton.
Recent results of neutrino oscillation experiments point to a nonvanishing neutrino mass. Neutrino mass models favour Majorana-type neutrinos. In such circumstances it is natural that the supersymmetric counterpart of the neutrino, the sneutrino, bears also lepton number violating properties. On the other hand, the fact that the universe exhibits an asymmetry in the baryon and antibaryon numbers poses constraints on the extent of lepton number violation in the light sneutrino sector if the electroweak phase transition is second or weak first order. From the requirement that the Baryon Asymmetr…
In the framework of a mass formula proposed previously (transforming in a specific way three free parameters into three masses), a simple empirical sum rule for three charged-lepton masses is found, predicting m_τ= 1776.9926 MeV, when the experimental values of m_e and m_μare used as an input. The experimental value to be compared with is m_τ= 1776.99^{+0.29}_{-0.26} MeV. This satisfactory sum rule (equivalent to a simple parameter constraint in the mass formula) is linear in masses and involves integers as its coefficients. The author believes that such a simple and precise mass sum rule for …
We analyze the possibility of measuring the single spin asymmetry (SSA) in open charm production by linearly polarized photons in the planned E160/E161 experiments at SLAC using the inclusive spectra of secondary (decay) leptons. In leading order pQCD, the SSA in the azimuthal distribution of the charged decay lepton is predicted to be about 0.2 for SLAC kinematics. Our calculations show that the SSA in the decay lepton distribution is well defined in pQCD: it is stable both perturbatively and parametrically, and practically insensitive to theoretical uncertainties in the charm semileptonic de…
The leading order contribution to the direct CP asymmetry in tau^{+/-} -> K^{+/-} pi^0 nu_{tau} decay rates is evaluated within the Standard Model. The weak phase required for CP violation is introduced through an interesting mechanism involving second order weak interactions, which is also responsible for tiny violations of the Delta S= Delta Q rule in K_{l3} decays. The calculated CP asymmetry turns out to be of order 10^{-12}, leaving a large window for studying effects of non-standard sources of CP violation in this observable.
One of the most robust relationships predicted by binary tetrahedral ($T^{'}$) flavor symmetry relates the reactor neutrino angle $θ_{13}$ to the atmospheric neutrino angle $θ_{23}$, independently of $θ_{12}$. It has the form $θ_{13} = \sqrt{2} |\fracπ{4} - θ_{23}|$. When this prediction first appeared in 2008, $θ_{13}$ was consistent with zero and $θ_{23}$ with $π/4$. Non-zero $θ_{13}$ was established by Daya Bay in 2012. Non-zero $|\fracπ{4}-θ_{23}|$ is now favored by the NO$ν$A experiment and, for $θ_{23}$, the aforementioned $T^{'}$ relation selects the second octant ($θ_{23} > \fracπ{4}$)…
We present a framework for lepton flavour models such that the first column of the lepton mixing matrix is (2,-1,-1)/sqrt(6). We show that the flavour symmetry group adequate for this purpose is S4. Our models are based on a vacuum alignment that can be obtained in a supersymmetric framework.
Baryon asymmetry can be generated at the first order electroweak phase transition, provided there is a CP violation on the bubble wall. In this report we discuss the role of leptons and quarks in the `non-local' baryogenesis mechanism.
Oscillations of active to sterile neutrinos with a small mixing angle sin 2 θ< 10^{-2} could generate a large lepton asymmetry in the Early Universe. The final order of magnitude of the lepton asymmetry ηis mainly determined by its growth in the last stage of evolution, the so called power-law regime. There exist two contradictory results in the literature, η\propto T^{-1} and η\propto T^{-4}, where T is the background medium temperature. In the first case, the lepton asymmetry does not exceed values of 10^{-4} for |δm^2| < 1 eV^2, while in the second case it can become larger than 10^{-1}. In…
We study charged lepton flavour violation in low-scale seesaw models of minimal supergravity, which realize large neutrino Yukawa couplings thanks to approximate lepton-number symmetries. There are two dominant sources of lepton flavour violation in such models. The first source originates from the usual soft supersymmetry-breaking sector, whilst the second one is entirely supersymmetric and comes from the supersymmetric neutrino Yukawa sector. Within the framework of minimal supergravity, we consider both sources of lepton flavour violation, soft and supersymmetric, and calculate a number of …
First Lattice QCD Determination of Lepton-Flavor-Universality Ratios in Light-Meson Leptonic Decays
Brookhaven National Laboratory（布鲁海文国家实验室）；The University of Edinburgh（爱丁堡大学）；Columbia University（哥伦比亚大学）；Peking University（北京大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；University of Connecticut（康涅狄格大学）；University of Southampton（南安普顿大学）
In this talk, we first make some brief comments on the phase-convention dependence of the CP-violating parameter ε_B. A simple framework is then presented for analyzing new physics contributions to B^0-\bar{B}^0 mixing and their effects on the lepton CP asymmetry, a promising signal to be further searched for in the first-round experiments of B factories.
The very recent Boomerang results give an estimate of unprecedented precision of the Cosmic Microwave Background anisotropies on sub--degree scales. A puzzling feature for theoretical cosmology is the low amplitude of the second acoustic peak. Through a qualitative discussion, we argue that a scarcely considered category of flat models, with a leptonic asymmetry, a high baryon density and a low cosmological constant seems to be in very good agreement with the data, while still being compatible with big bang nucleosynthesis and some other observational constraints. Although this is certainly no…
The application of fermion-boson symmetry to the standard model leads to the following: first, there are three generations of scalar quarks and scalar leptons in addition to the known quarks and leptons, and, secondly, the divergences in the perturbation series for the standard model are reduced. In the light of experimental data from LEP, Tevatron Collider, and LHC, some consequences of these two statements taken together are discussed. A series of experiments are proposed to search for the scalar quarks and scalar leptons at the Large Hadron Collider. The first step in this search is to look…
We consider the possibility of studying new physics that singles out the tau-lepton at the LHC. We concentrate on the tau-lepton charge asymmetry in tau+tau- pair production as a tool to probe this physics beyond the Standard Model. We consider two generic scenarios for the new physics. We first study a non-universal Z' boson as an example of a new resonance that can single out tau-leptons. We then consider vector lepto-quarks coupling of the first generation quarks with the third generation leptons as an example of non-resonant new physics. We find that in both cases the charge asymmetry can …
First of all, an importance of the LHC and FCC based energy frontier lepton-hadron and photon-hadron colliders is emphasised. Then arguments favoring existence of new heavy isosinglet down-type quarks and vector-like isosinglet or isodoublet leptons are presented, following by historical arguments favoring new (preonic) level of matter. The importance of Super-Charm factory and GeV energy proton linac for Turkey national road map is argued. Finally, several recommendations for ESPP2020 are suggested.
We investigate the impact of extra leptons on observed tensions in the muon $g-2$ and the first-row CKM unitarity. By introducing a new SU(2)$_L$ doublet lepton and a SU(2)$_L$ triplet lepton, we find that both of the tensions can be explained simultaneously under constraints from electroweak precision observables and Higgs-boson decays. Our model could be tested by measurements of $h\toμμ$ at future collider experiments.
We present the first extraction of the transversity distribution based on the global analysis of pion-pair production in deep-inelastic scattering and in proton-proton collisions with one transversely polarized proton. The extraction relies on the knowledge of di-hadron fragmentation functions, which are taken from the analysis of electron-positron annihilation data. For the first time, the chiral-odd transversity is extracted from a global analysis similar to what is usually done for the chiral-even spin-averaged and helicity distributions. The knowledge of transversity is important among oth…
