In various models of supersymmetry (SUSY), the lightest superparticle in the minimal SUSY standard model sector, which we call MSSM-LSP, becomes unstable. Then, we may observe the decay of the MSSM-LSP in the detector at the LHC experiment. We show that the discovery of such a decay process (and the determination of the lifetime of the MSSM-LSP) may be possible at the LHC even if the decay length of the MSSM-LSP is much longer than the size of the detector; sizable number of the MSSM-LSPs decay inside the detector if the lifetime is shorter than 0.01-1 millisec. We also discuss the implications of the study of the MSSM-LSP decay for several well-motivated SUSY models.
Long-lived stau shows up in various supersymmetric models, like gauge-mediated supersymmetry (SUSY) breaking model. At the LHC experiment, long-lived stau is useful not only for the discovery of SUSY signals but also for the study of the detailed properties of superparticles. We discuss a method to obtain information on spins and chiralities of superparticles in the framework with long-lived stau. We also show that such a study can be used to distinguish SUSY model from other models of new physics, like the universal extra dimension model.
In supersymmetric scenarios with a long-lived stau, the LHC experiments provide us with a great environment for precise mass measurements of superparticles. We study a case in which the mass differences between the lightest stau and other sleptons are about 10 GeV or larger, so that the decay products of heavier sleptons are hard enough to be detected. We demonstrate that the masses of neutralinos, sleptons, and squarks can be measured with a good accuracy.
Supersymmetry searches at the LHC are both highly varied and highly constraining, but the vast majority are focused on cases where the final-stage visible decays are prompt. Scenarios featuring superparticles with detector-scale lifetimes have therefore remained a tantalizing possibility for sub-TeV SUSY, since explicit limits are relatively sparse. Nonetheless, the extremely low backgrounds of the few existing searches for collider-stable and displaced new particles facilitates recastings into powerful long-lived superparticle searches, even for models for which those searches are highly non-…
We study the phenomenology of a supersymmetric scenario where the next-to-lightest superparticle is the lighter stau and long-lived due to a very weakly coupled lightest superparticle, such as the gravitino. We investigate the LHC sensitivity and its dependence on the superparticle spectrum with an emphasis on strong production and decay. We do not assume any high-scale model for SUSY breaking but work along the lines of simplified models. Devising cuts that yield a large detection efficiency in the whole parameter space, we determine the LHC's discovery and exclusion potential. This allows us…
Supersymmetric scenarios with a very weakly interacting lightest superparticle (LSP) - like the gravitino or axino - naturally give rise to a long-lived next-to-LSP (NLSP). In the case of a stau NLSP, the scenario shows up in a very prominent way at colliders. We present the LHC sensitivity for these classes of scenarios in the framework of simplified models. This allows for deriving robust limits on the masses of the lightest stau, the gluino and squarks.
Modification of standard big-bang nucleosynthesis is considered in the minimal supersymmetric standard model to resolve the excessive theoretical prediction of the abundance of primordial lithium 7. We focus on the stau as a next-lightest superparticle, which is long lived due to its small mass difference with the lightest superparticle. It provides a number of additional decay processes of $\mathrm{^{7}Li}$ and $\mathrm{^{7}Be}$. A particularly important process is the internal conversion in the stau-nucleus bound state, which destroys the $\mathrm{^{7}Li}$ and $\mathrm{^{7}Be}$ effectively. …
As the majority of LHC searches are focused on prompt signatures, specific long-lived particles have the potential to be overlooked by the otherwise systematic new physics programs at ATLAS and CMS. While in many cases long-lived superparticles are now stringently constrained by existing exotic searches, we point out that the highly motivated model of gauge mediation with staus as the next-to-lightest superparticle (NLSP) has received less attention. We recast LHC searches for heavy stable charged particles, disappearing tracks, and opposite-flavor leptons with large impact parameters to asses…
``Top--down'' models explain the observation of ultra high energy cosmic rays (UHECR; $E \gsim 5 \cdot 10^{19}$ eV) through the decay of very massive, long--lived ``$X$ particles''. If superparticles with masses near a TeV exist, $X$ decays also lead to a significant flux of very energetic neutralinos, assumed to be the (stable or long--lived) lightest superparticles. There is a range of energies where neutrinos get absorbed in the Earth, but neutralinos can still traverse it. These neutralinos could in principle be detected. We calculate the detection rate in planned experiments such as OWL a…
We consider constraints on long-lived charged scalar leptons \tilde{l}^\pm in supersymmetric models, where gravitino is the lightest superparticle. We study the decay and hadronization processes of \tilde{l}^\pm. We also take into account the significant enhancement of Li6 production due to the formation of the bound-state (He4 \tilde{l}^-); for this purpose, we use the reaction rate given by the most recent calculation based on coupled-channel method.
We consider supersymmetric models in which the neutral Wino is the lightest superparticle (LSP), and study the possibility that non-thermally produced Wino plays the role of dark matter. The thermal relic density of Wino is smaller than the present mass density of dark matter if wino mass is smaller than 2.9 TeV; however, even with smaller Wino mass, Wino can be the dominant component of dark matter if it is non-thermally produced by the decay of an exotic particle. In order to study such a possibility in detail, we perform a precise calculation of the present mass density of Wino produced by …
Cosmological issues are examined when gravitino is the lightest superparticle (LSP) and R-parity is broken. Decays of the next lightest superparticles occur rapidly via R-parity violating interaction, and thus they do not upset the big-bang nucleosynthesis, unlike the R-parity conserving case. The gravitino LSP becomes unstable, but its lifetime is typically much longer than the age of the Universe. It turns out that observations of diffuse photon background coming from radiative decays of the gravitino do not severely constrain the gravitino abundance, and thus the gravitino weighing less tha…
We perform an exhaustive study of the role neutrino telescopes could play in the discovery and exploration of supersymmetric extensions of the Standard Model with a long-lived stau next-to-lightest superparticle. These staus are produced in pairs by cosmic neutrino interactions in the Earth matter. We show that the background of stau events to the standard muon signal is negligible and plays no role in the determination of the cosmic neutrino flux. On the other hand, one can expect up to 50 pair events per year in a cubic kilometer detector such as IceCube, if the superpartner mass spectrum an…
We study the light-element abundances in supersymmetric model where the right-handed sneutrino is the lightest superparticle (LSP), assuming that the neutrino masses are purely Dirac-type. In such a scenario, the lightest superparticle in the minimal supersymmetric standard model sector (which we call MSSM-LSP) becomes long-lived, and thermal relic MSSM-LSP may decay after the big-bang nucleosynthesis starts. We calculate the light-element abundances including non-standard nuclear reactions induced by the MSSM-LSP decay, and derive constraints on the scenario of right-handed sneutrino LSP.
The differential cross section of the chargino-neutralino production, q qbar --> chi+- chi0, followed by their decays into scalar tau leptons, chi+- chi0 --> (stau+- nu)(stau-+ tau+-) --> (stau+- nu)(stau-+ l+- nu nubar), is calculated including the effect of spin correlations. In the case where stau is long-lived, this final state can be fully reconstructed in a hadron-collider experiment up to a discrete two-fold ambiguity. Distributions of various kinematic variables can thus be observable and tell us about masses and spins of superparticles and also parity/CP violation in interactions by c…
We study the role neutrino telescopes could play in discovering supersymmetric extensions of the Standard Model with a long-lived stau next-to-lightest superparticle. In such a setup, pairs of staus are produced by cosmic neutrino interactions in the Earth matter. In optimistic scenarios, one can expect several pair events per year in a cubic kilometer detector such as IceCube. We also show that no significant event rate can be expected for decays of staus stopped in the detector.
We study the prospect of determining the decay properties of the gluino in the supersymmetric (SUSY) standard model at a 100 TeV future hadron collider. We consider the case where the neutral Wino is the lightest superparticle. In this case, the long-lived charged Wino can be used to eliminate standard model backgrounds, which enables us to study the details of superparticles. We show that, based on the analysis of the numbers of high $p_T$ leptons, boosted $W$-jets, and $b$-tagged jets, we may determine the gaugino species and the quark flavors in the gluino decay. With such determinations, w…
We investigate the phenomenology of the gravitino dark matter scenario with a stau as the next-to-lightest supersymmetric particle at the LHC. For a wide range of gravitino masses the lighter stau is stable on the scale of a detector and gives rise to a prominent signature as a "slow muon". The direct stau production via the Drell-Yan process is always present and independent of the mass spectrum of the other superparticles, thus providing a lower bound for the discovery potential of this scenario. Performing a careful analysis with particular emphasis on the criteria for observing stau pairs …
It has been suggested that relic long-lived strongly interacting massive particles (SIMPs, or $X$ particles) existed in the early universe. We study effects of such long-lived unstable SIMPs on big bang nucleosynthesis (BBN) assuming that such particles existed during the BBN epoch, but then decayed long before they could be detected. The interaction strength between an $X$ particle and a nucleon is assumed to be similar to that between nucleons. We then calculate BBN in the presence of the unstable neutral charged $X^0$ particles taking into account the capture of $X^0$ particles by nuclei to…
We consider supersymmetric theories where the gravitino is the lightest superparticle (LSP). Assuming that the long-lived next-to-lightest superparticle (NSP) is a charged slepton, we investigate two complementary ways to prove the existence of supergravity in nature. The first is based on the NSP lifetime which in supergravity depends only on the Planck scale and the NSP and gravitino masses. With the gravitino mass inferred from kinematics, the measurement of the NSP lifetime will test an unequivocal prediction of supergravity. The second way makes use of the 3-body NSP decay. The angular an…
We study the effects of the unstable gravitino on the big-bang nucleosynthesis. If the gravitino mass is smaller than \sim 10 TeV, primordial gravitinos produced after the inflation are likely to decay after the big-bang nucleosynthesis starts, and the light element abundances may be significantly affected by the hadro- and photo-dissociation processes as well as by the p n conversion process. We calculate the light element abundances and derived upper bound on the reheating temperature after the inflation. In our analysis, we calculate the decay parameters of the gravitino (i.e., lifetime and…
We calculate the spectral distortions from Hawking evaporation of primordial black holes before the epoch of recombination, taking into account emission of all standard model particles, including quark and gluons, and evolving the resulting particle cascades in the expanding Universe. We show that the constraints on the abundance of primordial black holes are stronger by more than an order of magnitude compared to the previous calculations which take only the primary photon emission into account. We also show that the shapes of the spectral distortions is different from the $y$ or $i$-type dis…
It has been recently argued that localized, unstable, but extremely long-lived configurations, called oscillons, could affect the dynamics of a first order electroweak phase transition in an appreciable way. Treating the amplitude and the size of subcritical bubbles as statistical degrees of freedom, we show that thermal fluctuations are not strong enough to generate subcritical configurations able to settle into a an oscillon long-lived regime.
Time evolution of the decay process of unstable particles is investigated in field theory models. We first formulate how to renormalize the non-decay amplitude beyond perturbation theory and then discuss short-time behavior of very long-lived particles. Two different formalisms, one that does and one that does not, assume existence of the asymptotic field of unstable particles are considered. The non-decay amplitude is then calculated by introducing a finite time resolution of measurement, which makes it possible to discuss both renormalizable and non-renormalizable decay interaction including…
In the MSSM with gravity mediated supersymmetry breaking, there may exist unstable but long-lived solitons carrying large baryonic charge, or B-balls. These decay well afterthe electroweak phase transition, giving rise to B-ball baryogenesis. Being made of squarks, B-ball decays produce also LSPs and hence can be the source for all cold dark matter.
We study the implications of LHC results for the abundance of long-lived staus after freeze-out from thermal equilibrium in a super-WIMP dark matter scenario. We classify regions in the MSSM parameter space according to the stau yield, considering all possible co-annihilation effects as well as the effects of resonances and large Higgs-sfermion couplings. Afterwards, we examine the viability of these regions after imposing experimental and theoretical constraints, in particular a Higgs mass around 125 GeV and null-searches for heavy stable charged particles (HSCP) at the LHC. We work in a pMSS…
Although Planck data supports the standard ΛCDM model, it still allows for the presence of Dark Radiation corresponding up to about half an extra standard neutrino species. We propose a scenario for obtaining a fractional "effective neutrino species" from a thermally produced particle which decays into a much lighter stable relic plus standard fermions. At lifetimes much longer than 1 sec, both the relic particles and the non-thermal neutrino component contribute to Dark Radiation. By increasing the stable-to-unstable particle mass ratio, the relic particle no longer acts as Dark Radiation but…
We study effects of long-lived massive particles, which decay during the big-bang nucleosynthesis (BBN) epoch, on the primordial abundances of light elements. Compared to the previous studies, (i) the reaction rates of the standard BBN reactions are updated, (ii) the most recent observational data of light element abundances and cosmological parameters are used, (iii) the effects of the interconversion of energetic nucleons at the time of inelastic scatterings with background nuclei are considered, and (iv) the effects of the hadronic shower induced by energetic high energy anti-nucleons are i…
We investigate the phenomenological consequences of string models wherein the MSSM resides on a D-brane, and the hypercharge gaugino mass is generated in a geometrically separated hidden sector. This hypercharged anomaly-mediated SUSY breaking (HCAMSB) model naturally solves the tachyonic slepton mass problem endemic to pure AMSB scenarios. In HCAMSB, one obtains a mass ordering M_1>μ>M_2 with split left- and right- scalars, whereas in mAMSB models, one obtains μ>M_1>M_2 with nearly degenerate left- and right-scalars. We compute the allowed parameter space and expected superparticle mass spect…
In this paper, we point out a novel signature of physics beyond the Standard Model which could potentially be observed both at the Large Hadron Collider (LHC) and at future colliders. This signature, which emerges naturally within many proposed extensions of the Standard Model, results from the multiple displaced vertices associated with the successive decays of unstable, long-lived particles along the same decay chain. We call such a sequence of displaced vertices a "tumbler." We examine the prospects for observing tumblers at the LHC and assess the extent to which tumbler signatures can be d…
Institute of Physics, Jan Kochanowski University（扬·科哈诺夫斯基大学物理研究所）；Institute for Theoretical Physics, J. W. Goethe University（约翰·沃尔夫冈·歌德大学理论物理研究所）；Center for Exploration of Energy and Matter, Indiana University（印第安纳大学能量与物质探索中心）；Department of Physics, Indiana University（印第安纳大学物理系）
We propose a new physics scenario in which the decay of a very heavy dark-matter candidate which does not interact with the neutrino sector could explain the two anomalous events recently reported by ANITA. The model is composed of two components of dark matter, an unstable dark-sector state, and a massive dark gauge boson. We assume that the heavier dark-matter particle of EeV-range mass is distributed over the galactic halo and disintegrates into a pair of lighter -- highly boosted -- dark-matter states in the present universe which reach and penetrate the Earth. The latter scatters {\it in}…
We analyze the phenomenology of a prolonged early epoch of matter domination by an unstable but very long-lived massive particle. This new matter domination era can help to relax some of the requirements on the primordial inflation. Its main effect is the huge entropy production produced by the decays of such particle that can dilute any possible unwanted relic, as the gravitino in supersymmetric models, and thus relax the constraints on the inflationary reheating temperature. Furthermore, a long period of matter domination reduces the number of $e$-foldings after the horizon crossing by obser…
The "$μ$ from $ν$" supersymmetric standard model ($μν$SSM) cures the $μ$-problem and concurrently reproduces measured neutrino data by using a set of usual right-handed neutrino superfields. Recently, the LHC has revealed the first scalar boson which naturally makes it tempting to test $μν$SSM in the light of this new discovery. We show that this new scalar while decaying to a pair of unstable long-lived neutralinos, can lead to a distinct signal with non-prompt multileptons. With concomitant collider analysis we show that this signal provides an unmistakable signature of the model, pronounced…
We analyze the Sun as a source for the indirect detection of dark matter through a search for gamma rays from the solar disk. Capture of dark matter by elastic interactions with the solar nuclei followed by annihilation to long-lived mediators can produce a detectable gamma-ray flux. We search three years of data from the High Altitude Water Cherenkov Observatory and find no statistically significant detection of TeV gamma-ray emission from the Sun. Using this, we constrain the spin-dependent elastic scattering cross section of dark matter with protons for dark matter masses above 1 TeV, assum…
