Search

We examine the prospect of observing genuine lepton number violating (LNV) signals at hadron colliders in the context of the Type II seesaw mechanism. The model features smoking gun signals involving same-sign di-leptons and jets that may be the primary observable channel in certain regions of the parameter space. The flavour composition of final-state charged leptons in the minimal model is related to the origin of neutrino masses and is correlated with other rare processes, such as neutrinoless double beta decay. We review existing collider limits and provide sensitivity estimates from LNV signals at upcoming runs of the LHC, for zero and non-zero mass splittings between the scalar triplet components., Comment: 7 pages, 7 figures

We revisit the decay rate of the electroweak vacuum in the Standard Model with the full one-loop prefactor. We focus on the gauge degrees of freedom and derive the degeneracy factors appearing in the functional determinant using group theoretical arguments. Our treatment shows that the transverse modes were previously overcounted, so we revise the calculation of that part of the prefactor. The new result modifies the gauge fields' contribution by $7\%$ and slightly decreases the previously predicted lifetime of the electroweak vacuum, which remains much longer than the age of the universe. Our discussion of the transverse mode degeneracy applies to any calculation of functional determinants involving gauge fields in four dimensions., Comment: 5 pages + Supplemental, 2 figures

We consider a single real scalar field in flat spacetime with a polynomial potential up to $\phi^4$, that has a local minimum, the false vacuum, and a deeper global minimum, the true vacuum. When the vacua are almost degenerate we are in the thin wall regime, while as their difference in potential energy increases, we approach the thick wall regime. We give explicit simple formulae for the decay rate of the false vacuum in 3 and 4 spacetime dimensions. Our results include a careful treatment both of the bounce action, which enters at the exponent of the decay rate, and of the functional determinant at one loop, which determines the prefactor. The bounce action is computed analytically as an expansion in the thin wall parameter in generic $D$ dimensions. We find that truncating such an expansion at second order we obtain a remarkably accurate bounce action also deep into thick wall regimes. We calculate the functional determinant numerically in 3 and 4 dimensions and fit the results with simple polynomials of the same thin wall parameter. This allows us to write the complete one-loop decay rate as a compact expression, which works accurately from thin to thick wall regimes.

We develop a comprehensive implementation of the minimal Left-Right symmetric model within a FeynRules model file. We derive the complete set of mass spectra and mixings for the charged and neutral gauge bosons, would-be-Goldstones and gauge fixing, together with the ghost Lagrangian. In the scalar sector, we analytically re-derive all the massive states with mixings and devise a physical input scheme, which expresses the model couplings in terms of masses and mixing angles of all states. Fermion couplings are determined in closed form, including the Dirac mixing in the neutrino sector, evaluated explicitly with the Cayley-Hamilton method. We calculate the one loop next-to-leading QCD corrections and provide a complete UFO file for NLO studies, demonstrated on relevant benchmarks. We provide various restricted variants of the model file with different gauges, massless states, neutrino hierarchies and parity violating $g_L \neq g_R$ gauge couplings., Comment: 23 pages, 4 figures. For associated material, see http://sites.google.com/site/leftrighthep/ or http://feynrules.irmp.ucl.ac.be/wiki/LRSM_NLO

Temporary matter domination and late entropy dilution, injected by a "long-lived" particle in the early universe, serves as a standard mechanism for yielding the correct dark matter relic density. We recently pointed out the cosmological significance of diluting particle's partial decay into dark matter. When repopulated in such a way, dark matter carries higher momentum than its thermal counterpart, resulting in a suppression of the linear matter power spectrum that is constrained by the large scale structure observations. In this work, we study the impact of such constraints on the minimal left-right symmetric model that accounts for the origin of neutrino mass. We map out a systematic anatomy of possible dilution scenarios with viable parameter spaces, allowed by cosmology and various astrophysical and terrestrial constraints. We show that to accommodate the observed dark matter relic abundance the spontaneous left-right symmetry breaking scale must be above PeV and cosmology will continue to provide the most sensitive probes of it. In case the dilutor is one of the heavier right-handed neutrinos, it can be much lighter and lie near the electroweak scale., Comment: 48 pages, 11 figures

We study the production of right-handed $W_R$ bosons and heavy neutrinos $N$ at a future 100 TeV high energy hadron collider in the context of Left-Right symmetry, including the effects of $W_L-W_R$ gauge-boson mixing. We estimate the collider reach for up to 3/ab integrated luminosity using a multi-binned sensitivity measure. In the Keung-Senjanovi\'c and missing energy channels, the 3$\sigma$ sensitivity extends up to $M_{W_R}=35$ and 37 TeV, respectively. We further clarify the interplay between the missing energy channel and the (expected) limits from neutrinoless double beta decay searches, Big Bang nucleosynthesis and dark matter., Comment: 19 pages, version to appear in PRD

We present a fully analytical calculation of the false vacuum decay rate for a self-interacting scalar field in the thin-wall approximation. We obtain the bounce solution, together with the Euclidean action, counter-terms and renormalization group running, and we extract the functional determinant via the Gel'fand-Yaglom theorem. Our procedure is valid for a generic spacetime dimension $D$, and we provide an explicit finite renormalized decay rate in $D=3,4$., Comment: Conference proceedings for Corfu Summer Institute 2022 "School and Workshops on Elementary Particle Physics and Gravity", August 28 - October 1, 2022, Corfu, Greece. Based on arXiv:2202.04498

Entropy production is a necessary ingredient for addressing the over-population of thermal relics. It is widely employed in particle physics models for explaining the origin of dark matter. A long-lived particle that decays to the known particles, while dominating the universe, plays the role of the dilutor. We point out the impact of its partial decay to dark matter on the primordial matter power spectrum. For the first time, we derive a stringent limit on the branching ratio of the dilutor to dark matter from large scale structure observation using the SDSS data. This offers a novel tool for testing models with a dark matter dilution mechanism. We apply it to the left-right symmetric model and show that it firmly excludes a large portion of parameter space for right-handed neutrino warm dark matter., Comment: 6 pages, 4 figures. v2: added supplement material. Accepted for publication in Physical Review Letters

The existence of non-zero neutrino masses points to the likely existence of multiple SM neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as Heavy Neutral Leptons (HNLs). In this white paper we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding on key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios., Comment: 82 pages, 34 figures. Contribution to Snowmass 2021

We derive a closed-form false vacuum decay rate at one loop in the thin wall limit, where the true and false vacua are nearly degenerate. We obtain the bounce configuration in $D$ dimensions, together with the Euclidean action with a higher order correction, counter-terms and renormalization group running. We extract the functional determinant via the Gel'fand-Yaglom theorem for low and generic orbital multipoles. The negative and zero eigenvalues appear for low multipoles and the translational zeroes are removed. We compute the fluctuations for generic multipoles, multiply and regulate the orbital modes. We find an explicit finite renormalized decay rate in $D = 3, 4$ and give a closed-form expression for the finite functional determinant in any dimension., Comment: 22 pages plus 5 appendices, published in JHEP. In v4 we updated the final result in D=4, after the addition of a term missed in the previous versions. The result in D=3 is unchanged

We discuss an exact false vacuum decay rate at one loop for a real and complex scalar field in a quartic-quartic potential with two tree-level minima. The bounce solution is used to compute the functional determinant from both fluctuations. We obtain the finite product of eigenvalues and remove translational zero modes. The orbital modes are regularized with the zeta function and we end up with a complete renormalized decay rate. We derive simple expansions in the thin and thick wall limits and determine their validity., Comment: 34 pages, 2 figures, ancillary Mathematica notebook, v2: title change, added figure, references and explanations, accepted for publication in Phys. Rev. D

We are launching FindBounce, a Mathematica package for the evaluation of the Euclidean bounce action that enters the decay rate of metastable states in quantum and thermal field theories. It is based on the idea of polygonal bounces, which is a semi-analytical approach to solving the bounce equation by discretizing the potential into piecewise linear segments. This allows for a fast and robust evaluation of arbitrary potentials with specified precision and any number of scalar fields. Time cost grows linearly with the number of fields and/or the number of segments. Computation with 20 fields takes $\sim 2$ seconds with $0.5\%$ accuracy of the action. The FindBounce function is simple to use with the native Mathematica look and feel, it is easy to install, and comes with detailed documentation and physical examples, such as the calculation of the nucleation temperature. We also provide timing benchmarks with comparisons to existing tools, where applicable., Comment: 30 pages, 8 figures. Package homepage is available at https://github.com/vguada/FindBounce

We present a systematic comparison of doubly charged Higgs boson production mechanisms at hadron colliders in the context of the Type II Seesaw model, emphasizing the importance of higher-order corrections and subdominant channels. We consider the Drell-Yan channel at next-to-leading order in QCD, photon fusion at leading order, gluon fusion with resummation of threshold logarithms up to next-to-next-to-next-to-leading logarithmic accuracy, and same-sign weak boson fusion at next-to-leading order in QCD. For Drell-Yan processes, we study the impact of a static jet veto at next-to-leading order matched to the resummation of jet veto scale logarithms at next-to-next-to-leading logarithmic accuracy. For the photon fusion channel, the dependence on modeling photon parton distribution functions is definitively assessed. To model vector boson fusion at next-to-leading order, we include all interfering topologies at $\mathcal{O}(\alpha^4)$ and propose a method for introducing generator-level cuts within the MC@NLO formalism. Our results are obtained using a Monte Carlo tool chain linking the \textsc{FeynRules}, \textsc{NloCT} and \textsc{MadGraph5\_aMC@NLO} programs and have necessitated the development of new, publicly available, Universal FeynRules Output libraries that encode the interactions between the Type II Seesaw scalars and Standard Model particles. Libraries are compatible with both the normal and inverted ordering of Majorana neutrino masses., Comment: Journal version (27 pages, seven figures). Extended discussions on uncertainties and discovery potential. Type II Seesaw NLO FeynRules UFO available from https://feynrules.irmp.ucl.ac.be/wiki/TypeIISeesaw

Particles beyond the Standard Model (SM) can generically have lifetimes that are long compared to SM particles at the weak scale. When produced at experiments such as the Large Hadron Collider (LHC) at CERN, these long-lived particles (LLPs) can decay far from the interaction vertex of the primary proton-proton collision. Such LLP signatures are distinct from those of promptly decaying particles that are targeted by the majority of searches for new physics at the LHC, often requiring customized techniques to identify, for example, significantly displaced decay vertices, tracks with atypical properties, and short track segments. Given their non-standard nature, a comprehensive overview of LLP signatures at the LHC is beneficial to ensure that possible avenues of the discovery of new physics are not overlooked. Here we report on the joint work of a community of theorists and experimentalists with the ATLAS, CMS, and LHCb experiments --- as well as those working on dedicated experiments such as MoEDAL, milliQan, MATHUSLA, CODEX-b, and FASER --- to survey the current state of LLP searches at the LHC, and to chart a path for the development of LLP searches into the future, both in the upcoming Run 3 and at the High-Luminosity LHC. The work is organized around the current and future potential capabilities of LHC experiments to generally discover new LLPs, and takes a signature-based approach to surveying classes of models that give rise to LLPs rather than emphasizing any particular theory motivation. We develop a set of simplified models; assess the coverage of current searches; document known, often unexpected backgrounds; explore the capabilities of proposed detector upgrades; provide recommendations for the presentation of search results; and look towards the newest frontiers, namely high-multiplicity "dark showers", highlighting opportunities for expanding the LHC reach for these signals.

We propose a new approach for computing tunneling rates in quantum or thermal field theory with multiple scalar fields. It is based on exact analytical solutions of piecewise linear potentials with many segments that describes any given potential to arbitrary precision. The method is first developed for the single field case in 3 and 4 space-time dimensions and demonstrated on examples of classical potentials as well as the calculation of quantum fluctuations. A systematic expansion of the potential beyond the linear order is considered, taking into account higher order corrections, which paves the way for multiple scalar fields. We thereby provide a fast semi-analytical tool for evaluating the bounce action for theories with an extended scalar sector., Comment: 15 pages, 12 figures, polygonal bounces extended to multi-fields, computation of the prefactor, added references

In the context of Left-Right symmetry, we revisit the Keung-Senjanovi\'{c} production of right-handed $W_R$ bosons and heavy neutrinos $N$ at high energy colliders. We develop a multi-binned sensitivity measure and use it to estimate the sensitivity for the entire range of $N$ masses, spanning the standard and merged prompt signals, displaced vertices and the invisible $N$ region. The estimated sensitivity of the LHC with 300/fb integrated luminosity ranges from 5 to beyond 7 TeV, while the future 33(100) TeV collider's reach with 3/ab extends to 12(26) TeV., Comment: Added references, minor polishing

Collider signals of heavy Majorana neutrino mass origin are studied in the minimal Left-Right symmetric model, where their mass is generated spontaneously together with the breaking of lepton number. The right-handed triplet Higgs boson $\Delta$, responsible for such breaking, can be copiously produced at the LHC through the Higgs portal in the gluon fusion and less so in gauge mediated channels. At $\Delta$ masses below the opening of the $VV$ decay channel, the two observable modes are pair-production of heavy neutrinos via the triplet gluon fusion $gg \to \Delta \to NN$ and pair production of triplets from the Higgs $h \to \Delta \Delta \to 4N$ decay. The latter features tri- and quad same-sign lepton final states that break lepton number by four units and have no significant background. In both cases up to four displaced vertices may be present and their displacement may serve as a discriminating variable. The backgrounds at the LHC, including the jet fake rate, are estimated and the resulting sensitivity to the Left-Right breaking scale extends well beyond 10 TeV. In addition, sub-dominant radiative modes are surveyed: the $\gamma \gamma$, $Z \gamma$ and lepton flavour violating ones. Finally, prospects for $\Delta$ signals at future $e^+ e^-$ colliders are presented., Comment: 30 pages, 12 figures. v2: added clarifications and discussion on event selection, displacement, backgrounds; updated figures and added references, version as accepted in JHEP

The scalar sector of the minimal Left-Right model at TeV scale is revisited in light of the large quartic coupling needed for a heavy flavor-changing scalar. The stability and perturbativity of the effective potential is discussed and merged with constraints from low-energy processes. Thus the perturbative level of the Left-Right scale is sharpened. Lower limits on the triplet scalars are also derived: the left-handed triplet is bounded by oblique parameters, while the doubly-charged right-handed component is limited by the $h \to \gamma \gamma, Z \gamma$ decays. Current constraints disfavor their detection as long as $W_R$ is within the reach of the LHC., Comment: Added references, clarifications and acknowledgments

We show that within the Left-Right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs with the triplet that breaks parity. As a result, the Higgs can act as a gateway to the origin of heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign di-leptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches., Comment: 6 pages. Version matching PRL one. Updated references, minor clarifications, conclusions unchanged. Enjoy