Lepton flavor violating interactions are absent in the standard model but are expected in various beyond standard models. In this work, the potential of the future circular electron-positron collider to probe the four fermion lepton flavor couplings via the $e^{+}e^{-}\rightarrow e^{\pm}τ^{\mp}$ process is revisited by means of an effective field theory approach. We provide constraints at $95\%$ CL on the dimension-six Wilson coefficients including major sources of background processes and considering realistic detector effects at four expected operation energies $\sqrt{s}=157.5$, $162.5$, $240$ and $365$ GeV according to their corresponding integrated luminosities. We demonstrate that statistical combination of the results from four center-of-mass energies improves the sensitivity to the LFV couplings significantly. We compare the results with the prospects from Belle II with $50~ ab^{-1}$ and other studies at electron-positron colliders.
We investigate the prospects for discovering axion-like particles (ALPs) via a light-by-light (LBL) scattering at two colliders, the future circular collider (FCC-ee) and circular electron-positron collider (CEPC). The promising sensitivities to the effective ALP-photon coupling $g_{aγγ}$ are obtained. Our numerical results show that the FCC-ee and CEPC might be more sensitive to the ALPs with mass 2 GeV $\sim$ 10 GeV than the LHC and CLIC.
The psi(1P1) state can be produced at the Beijing Electron-Positron Collider (BEPC) in the process psi'-->psi(1P1)+pi(0). We calculate the rate of this process taking account of the S-D mixing effect in psi'. It is shown that the rate is about a factor of 3 smaller than the simple result without considering the S-D mixing effect. Possible detecting channels are suggested and it is shown that psi(1P1) is able to be found with the accumulation of 30 million events of psi' at BEPC.
Dark matter particles annihilating in the Galactic halo can provide a flux of positrons potentially observable in upcoming experiments, such as PAMELA and AMS-02. We discuss the spectral features which may be associated with dark matter annihilation in the positron spectrum and assess the prospects for observing such features in future experiments. Although we focus on some specific dark matter candidates, neutralinos and Kaluza-Klein states, we carry out our study in a model independent fashion. We also revisit the positron spectrum observed by HEAT.
If $R$-parity is broken and the photino, although unstable, does not decay within the detector, then in new semileptonic $B$-decay modes a light ($\sim$ 2--3 GeV) photino can be produced carrying missing energy. However, the photino, being massive, arranges a different kinematical configuration for the visible decay products as compared to a standard semileptonic event where the neutrino carries the missing energy. We study the above kinematic distributions in an attempt to explore the above scenario.
We present a general model-independent and rephase-invariant formalism that cleanly relates CP and CPT noninvariant observables to the fundamental parameters. Different types of CP and CPT violations in the K^0-, B^0-, B_s^0- and D^0-systems are explicitly defined. Their importance for interpreting experimental measurements of CP and CPT violations is emphasized. In particular, we show that the time-dependent measurements allow one to extract a clean signature of CPT violation.
There is no guarantee that the violation of lepton number, assuming it exists, will primarily manifest itself in neutrinoless double beta decay ($0νββ$). Lepton-number violation and lepton-flavor violation may be related, and much-needed information regarding the physics that violates lepton number can be learned by exploring observables that violate lepton flavors other than electron flavor. One of the most promising observables is $μ^- \rightarrow e^+$ conversion, which can be explored by experiments that are specifically designed to search for $μ^- \rightarrow e^-$ conversion. We survey lep…
We show that R-parity violating decay of Wino dark matter of mass \sim 3 TeV can naturally account for the flux and spectral shape of the cosmic-ray electrons and positrons observed by the PAMELA and Fermi satellites. To provide a theoretical basis for the scenario, we also present a model that trilinear R-parity breaking appears with a coefficient suppressed by powers of the gravitino mass, which naturally leads to the Wino lifetime of O(10^26) sec.
We consider theories where lepton flavor is violated, in particular concentrating on the four fermion operator consisting of three electrons and a tau. Strong constraints are available from existing searches for tau -> eee, requiring the scale of the contact interaction to be less than ~(9 TeV)^-2. We reexamine this type of physics, assuming that the particles responsible are heavy (with masses greater than ~TeV) such that a contact interaction description continues to be applicable at the energies for a future e+e- collider. We find that the process e+e- -> e tau can be a very sensitive probe…
In this talk, I review the status and prospects of several low energy flavor observables that are highly sensitive to New Physics effects. In particular I discuss the implications for possible New Physics in b --> s transitions coming from the recent experimental results on the B_s mixing phase, the branching ratio of the rare decay B_s --> mu+mu-, and angular observables in the B --> K* mu+mu- decay. Also the recent evidence for direct CP violation in singly Cabibbo suppressed charm decays and its interpretation in the context of New Physics models is briefly discussed.
We investigate the possibility of searching the lepton-flavor-violating (LFV) $τ\rightarrow μγ$ rare decay at the Super Charm-Tau Factory (CTF). By comparing the kinematic distributions of the LFV signal and the standard model (SM) background, we develop an optimized event selection criteria which can significantly reduce the background events. It is concluded that new $2 σ$ upper limit of about $1.9 \times 10^{-9}$ on $Br(τ\rightarrow μγ)$ can be obtained at the CTF, which is beyond the capability of Super-B factory in searching $τ$ lepton rare decay. Within the framework of the scalar leptoq…
Probing lepton flavor violating dark matter scenarios via astrophysical photons and positrons
South China Normal University（华南师范大学）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science（广东省基础与应用基础研究基金卓越学科中心，广东省核科学重点实验室）
The possibility to simulate lepton number violating supersymmetric models has been introduced into the recently updated PYTHIA event generator, now containing 1278 decay channels of SUSY particles into SM particles via lepton number violating interactions. This generator has been used in combination with the ATLFAST detector simulation to study the impact of lepton number violation (LV) on event topologies in the ATLAS detector, and trigger menus designed for LV-SUSY are proposed based on very general considerations. In addition, a rather preliminary analysis is presented on the possibility fo…
We analyze the lepton flavor violating decays $τ\rightarrow Pl$ ($P=π,η,η';\;l=e,μ$) in the scenario of the minimal R-symmetric supersymmetric standard model. The prediction on the branching ratios BR$(τ\rightarrow P e)$ and BR$(τ\rightarrow P μ)$ is affected by the mass insertion parameters $δ^{13}$ and $δ^{23}$, respectively. These parameters are constrained by the experimental bounds on the branching ratios BR($τ\rightarrow e (μ) γ$) and BR($τ\rightarrow 3e(μ)$). The result shows $Z$ penguin dominates the prediction on BR($τ\rightarrow Pl$) in a large region of the parameter space. The bran…
A general technique is presented for treating CPT violation in neutral-meson oscillations. The effective field theory for a complex scalar with CPT-violating operators of arbitrary mass dimension is incorporated in the formalism for the propagation and mixing of neutral mesons. Observable effects are discussed, and first measurements of CPT-violating operators of dimension five are extracted from existing experimental results.
The $μ^+ \to e^+ X$ decay, where $X$ is a dark sector boson, provides one of the strongest available bounds on the scale of dark sector interactions. The $X$ boson can be an axion or a dark photon. We show that the concurrent determination of the anti-muon and positron polarizations makes possible to distinguish with a confidence level of 99% between the two dark sector portals with as few as 6 observed events in the case of the massless dark photon. Instead, the massive spin-1, dimension 4 dark portal cannot be distinguished from the axion-like case. We also discuss the possibility that the $…
We consider the lepton-number-violating processes in $Λ_b$/$Λ_c$ decays mediated by on-shell GeV-scale sterile neutrino. We calculate the branching ratio for the following processes: $Λ_b^{0} \rightarrow \mathcal{B}^+ μ^{-}μ^- π^+$, where $\mathcal{B}^+$ is $Λ_c^+$ or proton, and $Λ_c^{+} \rightarrow Λμ^{+}μ^+ π^-$, as function of the mass of the sterile neutrino $m_N$ and the heavy-light mixing coefficient of the extended Pontecorvo-Maki-Nakagawa-Sakata (PMNS) matrix $|U_{μN}|^2$. The effect of finite detector size is included in our calculation. After comparing the theoretical effective bran…
We explore the possibility of using CP violation in B decays to detect the presence of physics beyond the Standard Model. We first study the possibility of new physics in the $B-\bar B$ mixing amplitude. We discuss a construction to extract information about the phase and magnitude of the new physics contribution, as well as the CKM parameters in a model independent way. We point out the difficulty of carrying through this program induced by hadronic uncertainties and discrete ambiguities, and suggest additional measurements to overcome these problems. We then study the possibility of new phys…
Although the Lepton Flavor Violating (LFV) decay $μ^+\to e^+ γ$ is forbidden in the Standard Model (SM), it can take place within various theories beyond the SM. If the branching ratio of this decay saturates its present bound [{\it i.e.,} Br$(μ^+ \to e^+γ)\sim 10^{-11}$], the forthcoming experiments can measure the branching ratio with high precision and consequently yield information on the sources of LFV. In this letter, we show that for polarized $μ^+$, by studying the angular distribution of the transversely polarized positron and linearly polarized photon we can derive information on the…
As a basic symmetry of Einstein's theory of special relativity, Lorentz invariance has withstood very strict tests. But there are still motivations for such tests. Firstly, many theories of quantum gravity suggest violations of Lorentz invariance at the Planck energy scale. Secondly, even minute deviations from Lorentz symmetry can accumulate as particle travel across large distances, leading to detectable effects at attainable energies. Thanks to their long baselines and high-energy emission, astrophysical observations provide sensitive tests of Lorentz invariance in the photon sector. In thi…
We consider possible leptonic three-body decays of spin-1/2, charge-asymmetric dark matter. Assuming a general Dirac structure for the four-fermion contact interactions of interest, we study the cosmic-ray electron and positron spectra and show that good fits to the current data can be obtained for both charged-lepton-flavor-conserving and flavor-violating decay channels. We find that different choices for the Dirac structure of the underlying decay operator can be significantly compensated by different choices for the dark matter mass and lifetime. The decay modes we consider provide differin…
For any new physics possibly emerging in the future B experiments, the problem is how to extract the signals from the SM background. We consider the decay $b\to s s\bar d$ which is very small in the SM. In the MSSM this decay is possibly accessible in the future experiments. In the supersymmetric models with R-parity violating couplings, this channel is not strictly constrained, thus being useful in obtaining bounds on the lepton-number violating couplings. A typical candidate for the suggested search is the $B^-\to K^-K^-π^+$ mode.
In this work, we propose a search for a single photon at \texttt{FASER} and \texttt{FASER2}, produced from decays of bino-like, sub-GeV lightest neutralinos in the theoretical framework of the R-parity-violating (RPV) Minimal Supersymmetric Standard Model (MSSM). We consider a list of representative benchmark scenarios with one or two non-vanishing RPV couplings. The photon has an energy $\mathcal{O}\left(0.1\right)-\mathcal{O}\left(1\right)$ TeV. We find a sensitivity reach for RPV couplings beyond the current bounds by orders of magnitude at \texttt{FASER} and \texttt{FASER2}.
We study lepton-flavor violating slepton production and decay at a future e^+e^- linear collider in context with the seesaw mechanism in mSUGRA post-LEP benchmark scenarios. The present knowledge in the neutrino sector as well as improved future measurements are taken into account. We calculate the signal cross-sections σ(e^{+/-}e^- -> l_β^{+/-} l_α^- \tildeχ_b^0 \tildeχ_a^0); l_δ=e, μ, τ; α=|= βand estimate the main background processes. Furthermore, we investigate the correlations of these signals with the corresponding lepton-flavor violating rare decays l_α -> l_β γ. It is shown that these…
We entertain the idea that a suitable background of cold (very low momentum) pseudoscalar particles or condensate, may trigger a background that effectively generates Lorentz-invariance violation. This aether-like background induces a Chern-Simons modification of QED. Physics is different in different frames and, in the rest frame of the pseudoscalar background, high momentum photons can decay into pairs. The threshold for such decay depends quadratically on the rest mass of the particles. This mechanism could explain in a natural way why antiprotons are absent in recent cosmic ray measurement…
We study new top flavor violating resonances that are singly produced in association with a top at the LHC. Such top flavor violating states could be responsible for the Tevatron top forward-backward asymmetry. Since top flavor violating states can directly decay to a top (or anti-top) and jet, and are produced in conjunction with another (oppositely charged) top, the direct signature of such states is a t j (or tbar j) resonance in t tbar j events. In general, these states can be very light and have O(1) couplings to the top sector so that they are copiously produced. We present a search stra…
The observance of parity conserving time reversal violation in light quark systems could signal the presence of physics beyond the Standard Model. I discuss the implications of low-energy time reversal tests for the existence of such T-violating, P-conserving (TVPC) interactions. I argue that searches for permanent electric dipole moments (EDM's) and direct TVPC searches provide complementary information on P-conserving T-violation. EDM searches yield constraints only under the assumption that parity symmetry is restored at the scale Lambda associated with new TVPC physics. If parity remains b…
We study constraints on light and feebly interacting bosons with lepton flavor violation from electron beam dump experiments. Scalar, vector, and dipole interactions of the bosons are analyzed, respectively, and excluded regions from the searches for decays into electron-positron pairs are derived. It is found that parameter regions unconstrained by flavor violating decays of muon can be excluded using the results of the E137 experiment. We also discuss the impact of the search for flavor violating decays of the light bosons in electron beam dump experiments.
Joint energy distribution of the bottom quark and antiquark from decays of the top quark and antiquark produced in the reaction $e^+ e^- \to t \bar{t}$ is studied. Main emphasis is put on $CP$-violation effects in the interaction of the photon and $Z$ boson with the top quarks. Energy asymmetries of $b$ and $\bar{b}$ quarks, which give access to the $CP$-violating terms, are considered. To estimate the magnitude of these asymmetries, the $CP$-violating $γt t $ and $Z t t$ couplings are calculated in one-loop model with exchange of the Higgs boson with the mass of $125$ GeV. Interaction of this…
We point out that, since the colliders initial states (e+ e-,p p, p pbar, ... ) carry a definite nonabelian flavor, electroweak radiative corrections to inclusive hard cross sections at the TeV scale are affected by peculiar Bloch-Nordsieck violating double logs. We recall the setup of soft cancellation theorems, and we analyze the magnitude of the noncancelling terms in the example of electron - positron annihilation into hadrons.
We propose a new idea to test a class of loop-induced neutrino mass mechanisms by searching for lepton number violating charged current processes with incident of a neutrino beam. The expected rates of these processes are estimated based on some theoretical assumptions. They turn out to be sizable so that detection of such processes could be possible at near detectors in future highly intense neutrino-beam facilities.
We study the lepton flavor violating process, $e+ T \to τ+T'$, at a few GeV. This process can be studied by experiments directing GeV scale electron or positron beams on internal or fixed targets. We study the effects of some low energy lepton flavor violating interactions on this process. We study the sensitivities of this process on these low energy lepton flavor violating interactions and compare them to the sensitivities of lepton flavor violating $τ$ decay processes. Comparing with $τ$ decay processes, this process provides another way to study the lepton flavor violating effects with $e-…
Lepton charge asymmetries can be used as an alternative means of searching for new physics. They are interesting because they are small in the Standard Model and therefore, necessarily evidence new physics. In this work we explore the use of lepton asymmetries as a probe of the flavour structure of the left-right symmetric model with spontaneous CP violation. We find that new physics may enhance the magnitude of $a_{SL}$ up to the precent level within the appropiate parameter space.
Lorentz violation has been a popular field in recent years in the search for new physics beyond the Standard Model. We present a general method to build all Lorentz-violating terms in gauge field theories, including ones involving operators of arbitrary mass dimension. Applying these results to two types of experiments in high-energy colliders, light-by-light scattering and deep-inelastic scattering, we extract first bounds on certain coefficients for Lorentz violation.
Systematic study of lepton-flavor-violating dark matter interactions via indirect detection in effective field theories
State Key Laboratory of Nuclear Physics and Technology, Institute of Quantum Matter, South China Normal University（华南师范大学量子物质研究院核物理与技术国家重点实验室）；Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter, Guangdong Provincial Key Laboratory of Nuclear Science（广东省基础与应用基础研究基金委物质结构与基本相互作用卓越中心广东省核科学重点实验室）
A benchmark CP-violating supersymmetric scenario (known in the literature as `CPX-scenario') is studied in the context of the Large Hadron Collider (LHC). It is shown that the LHC, with low to moderate accumulated luminosity, will be able to probe the existing `hole' in the $m_{h_1}$-$\tanβ$ plane, which cannot be ruled out by the Large Electron Positron Collider data. This can be done through associated production of Higgs bosons with top quark and top squark pairs leading to the signal \emph{dilepton + $\leq{5}$ jets (including 3 b-jets) + missing ${p_T}$}. Efficient discrimination of such a…
We present the most general (six-helicity) angular analysis of Bs -> V_1 (-> P_1P'_1) V_2 (-> P_2P'_2) (V_i is a vector meson, and P_i, P'_i are pseudoscalars). We focus on final states accessible to both Bs and Bsbar -- these are mainly bbar -> sbar penguin decays. We also derive the most general decay amplitude, and discuss the differences between it and that used by LHCb in its analysis of Bs -> phi phi. In the standard model, all CP violation is predicted to be small, so that the simple measurement of a sizeable CP-violating observable indicates the presence of new physics. A full fit to t…
Probing CP-Violating Neutral Triple Gauge Couplings at Electron-Positron Colliders
Tsung-Dao Lee Institute, Shanghai Jiao Tong University（上海交大东京镭研究所）；Department of Physics, King’s College London（伦敦国王学院物理系）；Theoretical Physics Department, CERN（欧洲核子研究中心理论物理部）；School of Physics and Astronomy, Shanghai Jiao Tong University（上海交通大学物理与天文学院）；Department of Physics, Tsinghua University（清华大学物理系）；Center for High Energy Physics, Peking University（北京大学高能物理中心）；School of Physics, Peking University（北京大学物理学院）
Spin density matrix of baryon-antibaryon pairs in electron-positron annihilation with $P$ and $CP$ violation including electron mass
Yunnan University（云南大学）；Institute of Modern Physics, Chinese Academy of Sciences（中国科学院近代物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Lanzhou University（兰州大学）
The decay $B^- \to K^- K^- π^+$ has been sugested as a test for minimal supersymmetric standard model and for supersymmetric models with R-parity violating couplings, in view of its extreme smallnesss in the standard model. We calculate two long distance contributions to this decay, that associated with $DD$ and $Dπ$ intermediate states and that induced by virtual $D$, $π$ mesons. The branching ratio due to these contributions is $6 \times 10^{-12}$, which is somewhat smaller than the standard model short distance result, leaving this decay free for the search of new physics.
Recent positron flux fraction measurements in cosmic-rays (CR) made by the AMS-02 satellite confirm and extends the evidence on the existence of a new (yet unknown) source of high energy positrons. To explain this excess, we use the gravitino of bilinear R-parity violating SUSY models as a decaying Dark Matter candidate, as the source of those high energy particles. Being a long lived weak-interacting and spin 3/2 particle, it offers several particularities which makes it an attractive candidate. We compute the electron, positron and $γ$-ray\ fluxes produced by each gravitino decay channel at …
The effect of new operators that give rise to CP-violating couplings of the type $Z t \bar{t}$ and $γt \bar{t}$ are examined at future electron positron Linear Colliders (FLC). The impact of these CP-violating interactions over Standard Model predictions was studied for the process e+ e^- -> t anti-t with the subsequent decays t -> b l+ nu_l and anti-t -> anti-b l- anti-nu_l, called as dilepton mode, and t -> b l^+ nu_l and anti-t -> anti-b anti-q q' or t -> b q anti-q' and anti-t -> anti-b l- anti-nu_l, called as single lepton mode, where the final leptons are l = e or mu, and the final quark…
We discuss possible implications of Exotic Stringy instantons for Baryon-violating signatures in future colliders. In particular, we discuss high-energy quarks collisions and $Λ-\barΛ$ transitions. In principle, $Λ-\barΛ$ process can be probed by high-luminosity electron-positron colliders. However, we find that an extremely high luminosity is needed in order to provide a (somewhat) stringent bound compared to the current data on $NN\rightarrow ππ,KK$. On the other hand, (exotic) instanton-induced six quark interactions can be tested in near future high-energy colliders beyond LHC, at energies…
The coming flavour precision era will allow to uncover various patterns of flavour violation in different New Physics scenarios. We discuss different classes of them. A simple extension of the Standard Model that generally introduces new sources of flavour and CP violation as well as right-handed currents is the addition of a U(1) gauge symmetry to the SM gauge group. In such Z' models correlations between various flavour observables emerge that could test and distinguish different Z' scenarios. A concrete model with flavour violating Z' couplings is the 331 model based on the gauge group SU(3…
We propose a new class of R-parity violating extension of MSSM with type II seesaw mechanism for neutrino masses where an unstable gravitino is the dark matter of the Universe. It decays predominantly into three leptons final states, thereby providing a natural explanation of the positron excess but no antiproton excess in the PAMELA experiment. The model can explain neutrino masses without invoking any high scale physics while keeping the pre-existing baryon asymmetry of the universe in tact.
High energy colliders provide a new unique way to determine the microscopic properties of the dark matter (DM). Weakly interacting massive particles (WIMPs) are widely considered as one of the best DM candidates. It is usually assumed that the WIMP couples to the SM sector through its interactions with quarks and leptons. In this paper, we investigate the DM pair production associated with a $Z$ boson in an effective field theory framework at the International Linear Collider (ILC), which can be used to study the interactions between the DM and leptons. For illustrative purposes, we present th…
A general theoretical framework that incorporates possible CPT and Lorentz violation in an extension of the standard model and in quantum electrodynamics has been developed over the last decade. The framework originates in the idea that CPT and Lorentz symmetry could be broken spontaneously in a more fundamental theory such as string theory. These symmetry violations are described in the standard-model extension by small terms in the Lagrangian. Various experiments can bound these quantities. They include Penning-trap experiments with electrons and positrons, Penning-trap experiments with prot…
We search for lepton flavour violating couplings via doubly charged bilepton (or doubly charged Higgs) exchange in electron-positron annihilation process $ \text{e}^{+}\text{e}^{-}\to μ^{+}μ^{-}, τ^{+}τ^{-}$ using CERN LEP data at the center of mass energies between 189-207 GeV. Standard model program ZFITTER has been used to calculate radiative corrections. We find that $g_{L}^{2}/M_{L}^{2}<O(10^{-6})GeV^{-2}$ at 95% C.L. for flavour violating scalar and vector bilepton couplings.
We discuss the parity-violating left-right asymmetries (LRAs) in Möller scattering at the International Linear Collider (ILC) induced by doubly charged Higgs bosons in models with $SU(2)_L$ triplet and singlet scalar bosons, which couple to the left- and right-handed charged leptons, respectively. These bosons are important in the scenarios for the generation of the neutrino mass. We demonstrate that the contributions to the LRAs from the triplet and singlet bosons are opposite to each other. In particular, we show that the doubly charged Higgs boson from the singlet scalar can be tested at th…
The presence of the top-pions $π_{t}^{0,\pm}$ in the low-energy spectrum is an inevitable feature of the topcolor scenario. Taking into account the constraints of the present experimental limit of the lepton flavor violating($LFV$) process $μ\to eγ$ on the free parameters of topcolor-assisted techicolor(TC2) models, we study the contributions of the neutral top-pion $π^{0}_{t}$ to the $LFV$ processes $μ^{+}μ^{-}\toτμ$ (or $τe$), $ γγ\toτμ$ (or $τe$), $e^{+} e^{-}\toτμ$, and $e γ\to e π_{t}^{0}\to e τμ(e)$ via the flavor changing ($FC$) couplings $π_{t}^{0}l_{i}l_{j}$ and discuss the possibilit…
The existence of Majorana neutrinos must lead to lepton-number violating processes, and the Majorana nature of neutrinos can only be experimentally verified via lepton-number violating processes. We propose a new approach to search for Majorana neutrinos at future electron-positron colliders by exploiting this feature. We investigate the $ΔL = 2$ like-sign dilepton production and find that lepton colliders with different center-of-mass energies have comparative advantages in resonant production of a Majorana neutrino in either light neutrino mass range or heavy mass range. At the future Circul…
We study the impact that future lepton flavor violating experiments will have on the viable parameter space of the scotogenic model. Within this model, the dark matter particle is assumed to be the lightest singlet fermion and two cases are considered depending on how its relic density is obtained: via self-annihilations or via coannihilations with the scalars. For each case, a scan over the parameter space of the model is used to obtain a large sample of viable points, which we subsequently analyze. We find that future lepton flavor violating experiments, in particular those searching for $μ\…
We discuss some generic properties of lepton number violating (\Lv) processes and their relation to different entries of the Majorana neutrino mass matrix. Present and near future experiments searching for these processes, except the neutrinoless double beta decay, are unable to probe light(eV mass region) and heavy(hundred GeV mass region) neutrinos. On the other hand due to the effect of a resonant enhancement, some of \Lv decays can be very sensitive to the intermediate mass neutrinos with typical masses in hundred MeV region. These neutrinos may appear as admixtures of the three active and…
We search for supersymmetric standard model realizations with extra singlets and extra $ U(1)$ using the heterotic string compactification on the $ Z_{6-II}$ orbifold with two Wilson lines. We analyze the vacuum restabilization mechanism for three representative Pati-Salam string models obtained in the literature and present detailed results for the effective superpotential compatible with the string selection rules. An automated selection of semi-realistic vacua along flat directions in the non-Abelian singlet modes field space is performed by requiring the presence of massless pairs of elect…
The flux of electron and positron cosmic rays measured by the space-based experiments PAMELA, AMS-02, CALET, DAMPE and Fermi-LAT shows an unexpected behaviour at high energies, in comparison with expectations from standard astrophysical sources. In particular, AMS-02 observations provide compelling evidence for a new source of positrons and electrons whose origin is still unknown. Plausible scenarios include either the contribution of dark matter or unresolved astrophysical sources, such as nearby pulsars. It has been shown that explanations based mostly on dark matter, tend to overproduce gam…
By exploiting the relatively long lifetime of the tau lepton, we propose several novel methods for searching for new physics at an electron-positron collider. We consider processes that involve final states consisting of a tau lepton pair plus two missing particles. The mass and spin of the new physics particles can be measured in 3-prong tau decays. The tau polarization, which reflects the coupling to new physics, can be measured from the $τ\to πν$ decay channel using the impact parameter distribution of the charged pion. We also discuss the corresponding backgrounds for these measurements, t…
