New Physics Opportunities for Long-Lived Particles at Electron-Proton Colliders

Future electron-proton collider proposals like the LHeC or the FCC-eh can supply 1/ab of collisions with a center-of-mass energy in the TeV range, while maintaining a clean experimental environment more commonly associated with lepton colliders. We point out that this makes electron-proton colliders ideally suited to probe BSM signatures with final states that look like "hadronic noise" in the high-energy, pile-up-rich environment of hadron colliders. We focus on the generic vector boson fusion production mechanism, which is available for all BSM particles with electroweak charges at mass scales far above the reach of most lepton colliders. This is in contrast to previous BSM studies at these machines, which focused on BSM processes with large production rates from the asymmetric initial state. We propose to exploit the unique experimental environment in the search for long-lived particle signals arising from Higgsinos or exotic Higgs decays. At electron-proton colliders, the soft decay products of long-lived Higgsinos can be explicitly reconstructed ("displaced single pion"), and very short lifetimes can be probed. We find that electron-proton colliders can explore significant regions of BSM parameter space inaccessible to other collider searches, with important implications for the design of such machines.Comment: 16 pages, 11 figure

Closing the light gluino gap with electron-proton colliders

The future electron-proton collider proposals, LHeC and FCC-he, can deliver $\mathcal{O}$(TeV) center-of-mass energy collisions, higher than most of the proposed lepton accelerators, with $\mathcal{O}$(ab$^{-1}$) luminosity, while maintaining a much cleaner experimental environment as compared to the hadron machines. This unique capability of $e^- p$ colliders can be harnessed in probing BSM scenarios giving final states that look like hadronic noise at $pp$ machines. In the present study, we explore the prospects of detecting such a prompt signal having multiple soft jets at the LHeC. Such a signal can come from the decay of gluino in RPV or Stealth SUSY, where there exists a gap in the current experimental search with $m_{\tilde{g}} \approx 50 - 70$ GeV. We perform a simple analysis to demonstrate that, with simple signal selection cuts, we can close this gap at the LHeC at 95 % confidence level, even in the presence of a reasonable systematic error. More sophisticated signal selection strategies and detailed knowledge of the detector can be used to improve the prospects of signal detection.Comment: 7 pages, 5 figure

TwInflation

The general structure of Hybrid Inflation remains a very well-motivated mechanism for lower-scale cosmic inflation in the face of improving constraints on the tensor-to-scalar ratio. However, as originally modeled, the "waterfall" field in this mechanism gives rise to a hierarchy problem ($\eta-$problem) for the inflaton after demanding standard effective field theory (EFT) control. We modify the hybrid mechanism and incorporate a discrete "twin" symmetry, thereby yielding a viable, natural and EFT-controlled model of non-supersymmetric low-scale inflation, "Twinflation". Analogously to Twin Higgs models, the discrete exchange-symmetry with a "twin" sector reduces quadratic sensitivity in the inflationary potential to ultra-violet physics, at the root of the hierarchy problem. The observed phase of inflation takes place on a hilltop-like potential but without fine-tuning of the initial inflaton position in field-space. We also show that all parameters of the model can take natural values, below any associated EFT-cutoff mass scales and field values, thus ensuring straightforward theoretical control. We discuss the basic phenomenological considerations and constraints, as well as possible future directions.Comment: 21 pages, 2 figure

Cosmology and Particle Physics Beyond the Standard Model

The Standard Models (SM) of particle physics and cosmology have been great successes so far, but various observational and theoretical hints point towards new physics beyond them. In this thesis, we first briefly discuss these shortcomings, including puzzles for the initial state of the early universe and how they can be solved via Cosmic Inflation. We then focus on constructing microscopic models for inflation which are theoretically natural, Effective Field Theory (EFT) controlled, and observationally consistent, while also looking for possible new signals. We develop a supersymmetric (SUSY) bi-axion model of high-scale inflation, in which the axionic structure originates from gauge symmetry in an extra dimension. While local SUSY is necessarily Higgsed at high scales during inflation we show that it can naturally survive down to the ~TeV scale in the current era in order to resolve the electroweak hierarchy problem. In the face of improving constraints on the tensor-to-scalar ratio, we also investigate inflation at lower energy scales via the very well-motivated mechanism of Hybrid Inflation. We construct a technically natural and EFT-controlled model for this, “Twinflation”, incorporating a discrete “twin” symmetry. If a SUSY extension of the SM does survive down to ~TeV scales, although not yet observed at the collider searches so far, it may have structures giving rise to novel Long-Lived Particle (LLP) signatures. LLPs also feature in a variety of other new physics scenarios. We show that future electron-proton colliders, forming an interesting hybrid of leptonic and hadronic colliders, can probe LLPs with soft decay products and very short lifetimes, thus offering a complimentary reach into the new physics parameter space

Closing the light gluino gap with electron-proton colliders

The future electron-proton collider proposals, LHeC and FCC-he, can deliver O(TeV) center-of-mass energy collisions, higher than most of the proposed lepton accelerators, with O(ab−1) luminosity, while maintaining a much cleaner experimental environment as compared to the hadron machines. This unique capability of e−p colliders can be harnessed in probing beyond the Standard Model scenarios giving final states that look like hadronic noise at pp machines. In the present study, we explore the prospects of detecting such a prompt signal having multiple soft jets at the LHeC. Such a signal can come from the decay of gluino in R-parity-violating or stealth supersymmetry, where there exists a gap in the current experimental search with m ˜ g≈50–70  GeV. We perform a simple analysis to demonstrate that, with simple signal selection cuts, we can close this gap at the LHeC at the 95% confidence level, even in the presence of a reasonable systematic error. More sophisticated signal selection strategies and detailed knowledge of the detector can be used to improve the prospects of signal detection

Report from Working Group 3: Beyond the standard model physics at the HL-LHC and HE-LHC

This is the third out of five chapters of the final report [1] of the Workshop on Physics at HL-LHC, and perspectives on HE-LHC [2]. It is devoted to the study of the potential, in the search for Beyond the Standard Model (BSM) physics, of the High Luminosity (HL) phase of the LHC, defined as $3$ ab$^{-1}$ of data taken at a centre-of-mass energy of 14 TeV, and of a possible future upgrade, the High Energy (HE) LHC, defined as $15$ ab$^{-1}$ of data at a centre-of-mass energy of 27 TeV. We consider a large variety of new physics models, both in a simplified model fashion and in a more model-dependent one. A long list of contributions from the theory and experimental (ATLAS, CMS, LHCb) communities have been collected and merged together to give a complete, wide, and consistent view of future prospects for BSM physics at the considered colliders. On top of the usual standard candles, such as supersymmetric simplified models and resonances, considered for the evaluation of future collider potentials, this report contains results on dark matter and dark sectors, long lived particles, leptoquarks, sterile neutrinos, axion-like particles, heavy scalars, vector-like quarks, and more. Particular attention is placed, especially in the study of the HL-LHC prospects, to the detector upgrades, the assessment of the future systematic uncertainties, and new experimental techniques. The general conclusion is that the HL-LHC, on top of allowing to extend the present LHC mass and coupling reach by $20-50\%$ on most new physics scenarios, will also be able to constrain, and potentially discover, new physics that is presently unconstrained. Moreover, compared to the HL-LHC, the reach in most observables will, generally more than double at the HE-LHC, which may represent a good candidate future facility for a final test of TeV-scale new physics