We study non-perturbatively the time evolution of cascade decay for generic fields $π\rightarrow ϕ_1ϕ_2\rightarrow ϕ_2χ_1χ_2$ and obtain the time dependence of amplitudes and populations for the resonant and final states. We analyze in detail the different time scales and the manifestation of unitary time evolution in the dynamics of production and decay of resonant intermediate and final states. The probability of occupation (population) "flows" as a function of time from the initial to the final states. When the decay width of the parent particle $Γ_π$ is much larger than that of the intermediate resonant state $Γ_{ϕ_1}$ there is a "bottleneck" in the flow, the population of resonant states builds up to a maximum at $t^* = \ln[Γ_π/Γ_{ϕ_1}]/(Γ_π-Γ_{ϕ_1})$ nearly saturating unitarity and decays to the final state on the longer time scale $1/Γ_{ϕ_1}$. As a consequence of the wide separation of time scales in this case the cascade decay can be interpreted as evolving sequentially $π\rightarrow ϕ_1ϕ_2; ~ ϕ_1ϕ_2\rightarrow ϕ_2χ_1χ_2$. In the opposite limit the population of resonances ($ϕ_1$) does not build up substantially and the cascade decay proceeds almost directly from the initial parent to the final state without resulting in a large amplitude of the resonant state. An alternative but equivalent non-perturbative method useful in cosmology is presented. Possible phenomenological implications for heavy sterile neutrinos as resonant states and consequences of quantum entanglement and correlations in the final state are discussed.
We propose a novel algorithm to compute the width of any generic $n$-body decay involving multiple off-shell particles having zero and non-zero spins. Starting from a toy example, we show the computations for three different processes that contain spin-0, $\frac{1}{2}$, and 1 off-shell particles. We have checked that our results match with the existing results at the analytical level. This proposal can be automatized and should be useful to compute the phase space for long cascade decays, without any Monte Carlo sampling.
We propose a simplified model to study the possible new heavy diphoton resonance from cascade decay of a heavier particle at colliders, which may be related to the dark matter or other new physics beyond the standard model. Model-independent constraints and predictions on the allowed couplings for generating the observed diphoton data are studied in detail. We demonstrate that this scenario can be tested by the possible four-photon signal or the $WW/ZZ/Zγ$ resonances. Meanwhile, this cascade decay scenario also provides us with the dark matter candidates, which is consistent with the observed …
In an earlier paper we have proposed a novel method to compute the decay width for a general $1\to n$ cascade decay where the propagators are off-shell and may be of different spins. Here, we extend our algorithm to accommodate those decays that are mediated by more than one such cascades. This generalizes our prescription and widens its applicability. We compute the three- and four-body toy decay chains where identical final states appear through different cascades. Here, we also provide the algorithm to calculate the interference terms. For four-body decays we discuss both symmetric and asym…
We analyze joint angular distributions of a charmonium decay to the $Ξ\barΞ$ pair using the $Ξ\toΛπ\to pπ^-π$ weak decay chain for the cascade and the charge conjugated mode for the anticascade. The decays allow a direct comparison of the baryon and antibaryon decay properties and a sensitive test of CP symmetry in the strange baryon sector. We show that all involved decay parameters can be determined separately in vector and (pseudo)scalar charmonia decays into $Ξ\barΞ$ due to the spin correlations between the weak decay chains. Contrary to the recently measured $e^+e^-\to J/ψ\to Λ\barΛ$ proc…
We present expressions for the kinematic endpoints of 5-body cascade decay chains proceeding through all possible combinations of 2-body and 3-body decays, with one stable invisible particle in the final decay stage. When an invariant mass can be formed in multiple ways by choosing different final state particles from a common vertex, we introduce techniques for finding the sub-leading endpoints for all indistinguishable versions of the invariant mass. In contrast to short decay chains, where sub-leading endpoints are linearly related to the leading endpoints, we find that in 5-body decays, th…
Beyond the Standard Model scenarios with extensions of the Higgs sector typically predict new resonances that can undergo a series of cascade decays to detectable Standard Model particles. On one hand, sensitivity to such signatures will contribute to the full reconstruction of the extended Higgs potential if a new physics discovery will be made. On the other hand, such cascade decays could be dominant decay channels, thus being potentially the best motivated signatures to achieve a new physics discovery in the first place. In this work, we show how the long short-term memory that is encoded i…
Kinematic edges of cascade decays of new particles produced in high-energy collisions may provide important constraints on the involved particles' masses. For the exemplary case of gluino decay $\tilde{g}\to q\bar q \tildeχ$ into a pair of quarks and a neutralino through a squark resonance, we study the hadronic invariant mass distribution in the vicinity of the kinematic edge. We perform a next-to-leading order calculation in the strong coupling $α_s$ and the ratio of squark width and squark mass $Γ_\tilde{q}/m_\tilde{q}$, based on a systematic expansion in $Γ_\tilde{q}/m_\tilde{q}$. The sepa…
Recent high-energy cosmic $e^\pm$ measurement from the DArk Matter Particle Explorer (DAMPE) satellite confirms the deviation of total cosmic ray electron spectrum above 700-900 GeV from a simple power law. In this paper we demonstrate that the cascade decay of dark matter (DM) can account for DAMPE's TeV $e^+e^-$ spectrum. We select the least constraint DM decay channel into four muons as the benchmark scenario, and perform an analysis with propagation variance in both DM signal and the Milky Way's electron background. The best-fit of the model is obtained for joint DAMPE, Fermi-Large Area Te…
Collider events with multi-stage cascade decays fill out the kinematically allowed region in phase space with a density that is enhanced at the boundary. The boundary encodes all available information about the spectrum and is well populated even with moderate signal statistics due to this enhancement. In previous work, the improvement in the precision of mass measurements for cascade decays with three visible and one invisible particles was demonstrated when the full boundary information is used instead of endpoints of one-dimensional projections. We extend these results to cascade decays wit…
The IceCube Neutrino Observatory detects high energy astrophysical neutrinos in two event topologies: tracks and cascades. Since the flavor composition of each event topology differs, tracks and cascades can be used to test the neutrino properties and the mechanisms behind the neutrino production in astrophysical sources. Assuming a conventional model for the neutrino production, the IceCube data sets related to the two channels are in $>3σ$ tension with each other. Invisible neutrino decay with lifetime $τ/m=10^2$ s/eV solves this tension. Noticeably, it leads to an improvement over the stand…
We investigate the LHC discovery prospects for a heavy Higgs boson decaying into the Standard Model Higgs boson and additional weak bosons. We consider a generic model-independent new physics configuration where this decay proceeds via a cascade involving other intermediate scalar bosons and focus on an LHC final-state signature comprised either of four b-jets and two charged leptons or of four charged leptons and two b-jets. We design two analyses of the corresponding signals, and demonstrate that a 5σ discovery at the 14 TeV LHC is possible for various combinations of the parent and daughter…
We study cascade decays of heavy neutral Higgs bosons through vectorlike quarks. We focus on scenarios where decay modes into pairs of vectorlike quarks are not kinematically open which extends the sensitivity of the LHC to larger masses. Assuming only mixing with the third family of standard model quarks the new decay modes of heavy Higgs bosons are: $H\to t_4 t \to Wbt, Zt t, ht t$ and $H\to b_4 b \to Wtb, Zb b, hb b$, where $t_4$ ($b_4$) is the new up-type (down-type) quark mass eigenstate. In the numerical analysis we assume the CP even Higgs boson in the two Higgs doublet model type-II bu…
Current constraints on energy injection in the form of energetic particles before the epoch of recombination using CMB spectral distortions assume that all energy goes into $y$ and $μ$-type distortions. We revisit these constraints with exact calculations of the spectral distortions by evolving the electromagnetic cascades. The actual spectral distortion differs in shape and amplitude from the $y$-type distortion and depends on the energy and nature of injected particles. The constraints on the energy injection processes such as dark matter decay can be relaxed by as much as a factor of 5.
