publications

2023

1. Nucl. Phys. B

   A survey of family unification models with bifundamental matter

   Elijah Sheridan, and Thomas W Kephart

   Nuclear Physics B, 2023

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   Extensions of the Standard Model have been attempted from the bottom up and from the top down, yet there remains a largely unexplored middle ground. In this paper, using the Mathematica package LieART, we exhaustively enumerate embeddings of the Standard Model within the class of theories with bifundamental fermions in the product gauge group SU(a) \times SU(b) \times SU(c), with no more generators than E_6, while achieving SM family unification rather than replication. We incorporate simple phenomenological constrains and find 151 unique models, including 9 that have only vector-like particle content beyond the Standard Model (BSM), which we conjecture belong to 5 infinite families of such models. We describe the most viable models: namely, the 9 with strictly vector-like BSM content along with the 29 models we found with no more than 30 BSM chiral particles. These include models with fractional electric charge color singlets, and hence magnetic monopoles with multiple Dirac charge. This latter collection of models predicts chiral particles with masses near the electroweak scale accessible to current and future collider experiments.

   @article{sheridan2023survey,
     title = {A survey of family unification models with bifundamental matter},
     author = {Sheridan, Elijah and Kephart, Thomas W},
     journal = {Nuclear Physics B},
     volume = {987},
     pages = {116108},
     year = {2023},
     publisher = {North-Holland},
   }

2. EPJ C

   Probing a Z′ with non-universal fermion couplings through top quark fusion, decays to bottom quarks, and machine learning techniques

   Diego Barbosa, Felipe Dı́az, Liliana Quintero, and 5 more authors

   The European Physical Journal C, 2023

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   The production of heavy neutral mass resonances, \textrmZ^\prime, has been widely studied theoretically and experimentally. Although the nature, mass, couplings, and associated quantum numbers of this hypothetical particle are yet to be determined, current LHC experimental results have set strong constraints assuming the simplest beyond Standard Model (SM) hypotheses. We present a new feasibility study on the production of a \textrmZ^\prime boson at the LHC, with family non-universal couplings, considering proton-proton collisions at \sqrts = 13 and 14 TeV. Such a hypothesis is well motivated theoretically and it can explain observed differences between SM predictions and experimental results, as well as being a useful tool to further probe recent results in searches for new physics considering non-universal fermion couplings. We work under two simplified phenomenological frameworks where the \mathrmZ^\prime masses and couplings to the SM particles are free parameters, and consider final states of the \textrmZ^\prime decaying to a pair of \mathrmb quarks. The analysis is performed using machine learning techniques to maximize the sensitivity. Despite being a well motivated physics case in its own merit, such scenarios have not been fully considered in ongoing searches at the LHC. We note the proposed search methodology can be a key mode for discovery over a large mass range, including low masses, traditionally considered difficult due to experimental constrains. In addition, the proposed search is complementary to existing strategies.

   @article{barbosa2023probing,
     title = {Probing a Z′ with non-universal fermion couplings through top quark fusion, decays to bottom quarks, and machine learning techniques},
     author = {Barbosa, Diego and D{\'\i}az, Felipe and Quintero, Liliana and Fl{\'o}rez, Andr{\'e}s and Sanchez, Manuel and Gurrola, Alfredo and Sheridan, Elijah and Romeo, Francesco},
     journal = {The European Physical Journal C},
     volume = {83},
     number = {5},
     pages = {413},
     year = {2023},
     publisher = {Springer Berlin Heidelberg Berlin/Heidelberg},
   }

2021

1. 

   Probing axionlike particles with γγfinal states from vector boson fusion processes at the LHC

   Andrés Flórez, Alfredo Gurrola, Will Johns, and 4 more authors

   Physical Review D, 2021

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   We perform a feasibility study to search for axion-like particles (ALPs) using vector boson fusion (VBF) processes at the LHC. We work in an effective field theory framework with cutoff scale Λand ALP mass m_a , and assume that ALPs couple to photons with strength ∝1/Λ. Assuming proton-proton collisions at \sqrts = 13 TeV, we present the total VBF ALP production cross sections, ALP decay widths and lifetimes, and relevant kinematic distributions as a function of m_a and Λ. We consider the a\toγγdecay mode to show that the requirement of an energetic diphoton pair combined with two forward jets with large dijet mass and pseudorapidity separation can significantly reduce the Standard Model backgrounds, leading to a 5σdiscovery reach for 10 \text MeV ≲m_a ≲1 TeV with Λ≲2 TeV, assuming an integrated luminosity of 3000 fb^-1. In particular, this extends the LHC sensitivity to a previously unstudied region of the ALP parameter space.

   @article{florez2021probing,
     title = {Probing axionlike particles with $\gamma\gamma$ final states from vector boson fusion processes at the LHC},
     author = {Fl{\'o}rez, Andr{\'e}s and Gurrola, Alfredo and Johns, Will and Sheldon, Paul and Sheridan, Elijah and Sinha, Kuver and Soubasis, Brandon},
     journal = {Physical Review D},
     volume = {103},
     number = {9},
     pages = {095001},
     year = {2021},
     publisher = {American Physical Society},
     dimensions = {true},
   }

2. JCAP

   Magnetars and axion-like particles: probes with the hard X-ray spectrum

   Jean-François Fortin, Huai-Ke Guo, Steven P Harris, and 2 more authors

   Journal of Cosmology and Astroparticle Physics, 2021

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   Quiescent hard X-ray and soft gamma-ray emission from neutron stars constitute a promising frontier to explore axion-like-particles (ALPs). ALP production in the core peaks at energies of a few keV to a few hundreds of keV; subsequently, the ALPs escape and convert to photons in the magnetosphere. The emissivity goes as ∼T^6 while the conversion probability is enhanced for large magnetic fields, making magnetars, with their high core temperatures and strong magnetic fields, ideal targets for probing ALPs. We compute the energy spectrum of photons resulting from conversion of ALPs in the magnetosphere and then compare it against hard X-ray data from NuSTAR, INTEGRAL, and XMM-Newton, for a set of eight magnetars for which such data exists. Upper limits are placed on the product of the ALP-nucleon and ALP-photon couplings. For the production in the core, we perform a calculation of the ALP emissivity in degenerate nuclear matter modeled by a relativistic mean field theory. The reduction of the emissivity due to improvements to the one-pion exchange approximation is incorporated, as is the suppression of the emissivity due to proton superfluidity in the neutron star core. A range of core temperatures is considered, corresponding to different models of the steady heat transfer from the core to the stellar surface. For the subsequent conversion, we solve the coupled differential equations mixing ALPs and photons in the magnetosphere. The conversion occurs due to a competition between the dipolar magnetic field and the photon refractive index induced by the external magnetic field. Semi-analytic expressions are provided alongside the full numerical results. We also present an analysis of the uncertainty on the axion limits we derive due to the uncertainties in the magnetar masses, nuclear matter equation of state, and the proton superfluid critical temperature.

   @article{fortin2021magnetars,
     title = {Magnetars and axion-like particles: probes with the hard X-ray spectrum},
     author = {Fortin, Jean-Fran{\c{c}}ois and Guo, Huai-Ke and Harris, Steven P and Sheridan, Elijah and Sinha, Kuver},
     journal = {Journal of Cosmology and Astroparticle Physics},
     volume = {2021},
     number = {06},
     pages = {036},
     year = {2021},
     publisher = {IOP Publishing},
   }