arXiv subjects

James A. Maxin

Publications and source records attributed to James A. Maxin.

At least 19 recordsLinked to original sources

arXiv2025

Light right-handed Smuons at the LHC: Natural dark matter and $g_μ-2$ in an unexplored realm of the pMSSM

We introduce an in-depth study of an unprobed pMSSM region offering a natural solution to dark matter. Since the 1980s this region has been referred to as the "bulk", consisting of sub 200 GeV neutralinos and right-handed smuons. The bulk satisfies recent muon $g_μ-2$ measurements and sustains consistency with $all$ presently operating SUSY experiments and LHC constraints. Initial ingress into the bulk will arrive soon via the LUX-ZEPLIN 1000-day experiment. The ATLAS Collaboration at the LHC has confirmed that observation of these light right-handed smuon events can occur at the ongoing LHC Run 3 and forthcoming High-Luminosity LHC. Moreover, the future FCC-ee and CEPC circular colliders should handily observe the events.

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arXiv2024

The Right-Handed Slepton Bulk Region for Dark Matter in Generalized No-scale $\mathcal{F}$-$SU(5)$ with Effective Super-Natural Supersymmetry

We propose Generalized No-Scale Supergravity, the simplest scenario for Effective Super-Natural Supersymmetry, naturally solving the supersymmetry electroweak fine-tuning problem and including natural dark matter. A light right-handed slepton bulk region is realized in $\mathcal{F}$-$SU(5)$ and the pMSSM. The bulk may be beyond the LHC reach, though can be probed at the 1000-day LUX-ZEPLIN, Future Circular Collider (FCC-ee) at CERN, Circular Electron Positron Collider (CEPC), and Hyper-Kamiokande.

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arXiv2021

Spinning No-Scale $\cal{F}$-$SU$(5) in the Right Direction

The Fermi National Accelerator Laboratory (FNAL) recently announced confirmation of the Brookhaven National Lab (BNL) measurements of the $g-2$ of the muon that uncovered a discrepancy with the theoretically calculated Standard Model value. We suggest an explanation for the combined BNL+FNAL 4.2$σ$ deviation within the supersymmetric grand unification theory (GUT) model No-Scale $\cal{F}$-$SU(5)$ supplemented with a string derived TeV-scale extra $10+\overline{10}$ vector-like multiplet and charged vector-like singlet $(XE,XE^c)$, dubbed flippons. We introduced these vector-like particles into No-Scale Flipped $SU(5)$ many years ago, and as a result, the renormalization group equation (RGE) running was immediately shaped to produce a distinctive and rather beneficial two-stage gauge coupling unification process to avoid the Landau pole and lift unification to the string scale, in addition to contributing through 1-loop to the light Higgs boson mass. The flippons have long stood ready to tackle another challenge, and now do so yet again, where the charged vector-like "lepton"/singlet couples with the muon, the supersymmetric down-type Higgs $H_d$, and a singlet $S$, using a chirality flip to easily accommodate the muonic $g-2$ discrepancy in No-Scale $\cal{F}$-$SU(5)$. Considering the phenomenological success of this string derived model over the prior 11 years that remains accommodative of all presently available LHC limits plus all other experimental constraints, including no fine-tuning, and the fact that for the first time a Starobinsky-like inflationary model consistent with all cosmological data was derived from superstring theory in No-Scale Flipped $SU(5)$, we believe it is imperative to reconcile the BNL+FNAL developments within the model space.

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arXiv2021

Resolving the $(g-2)_μ$ Discrepancy with $\cal{F}$-$SU$(5) Intersecting D-branes

A discrepancy between the measured anomalous magnetic moment of the muon $(g - 2)_μ$ and computed Standard Model value now stands at a combined $4.2σ$ following experiments at Brookhaven National Lab (BNL) and the Fermi National Accelerator Laboratory (FNAL). A solution to the disagreement is uncovered in flipped $SU(5)$ with additional TeV-Scale vector-like $\bf 10 + \overline{10}$ multiplets and charged singlet derived from local F-Theory, collectively referred to as $\cal{F}$-$SU(5)$. Here we engage general No-Scale supersymmetry (SUSY) breaking in $\cal{F}$-$SU(5)$ D-brane model building to alleviate the $(g - 2)_μ$ tension between the Standard Model and observations. A robust $Δa_μ$(SUSY) is realized via mixing of $M_5$ and $M_{1X}$ at the secondary $SU(5) \times U(1)_X$ unification scale in $\cal{F}$-$SU(5)$ emanating from $SU(5)$ breaking and $U(1)_X$ flux effects. Calculations unveil $Δa_μ({\rm SUSY}) = 19.0 - 22.3 \times 10^{-10}$ for gluino masses of $M(\widetilde{g}) = 2.25 - 2.56$ TeV and higgsino dark matter, aptly residing within the BNL+FNAL $1σ$ mean. This $(g - 2)_μ$ favorable region of the model space also generates the correct light Higgs boson mass and branching ratios of companion rare decay processes, and is further consistent with all LHC Run 2 constraints. Finally, we examine the heavy SUSY Higgs boson in light of recent LHC searches for an extended Higgs sector.

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arXiv2019

The Heavy Gluino in Natural No-Scale $\cal{F}$-$SU$(5)

In light of recent 80-137 $\rm{fb}^{-1}$ results at the LHC Run 2 establishing a lower gluino mass limit of 2.25 TeV, we revisit the supersymmetric GUT model Flipped $SU$(5) with extra vector-like particles, known as $\cal{F}$-$SU$(5), with vanishing No-Scale Supergravity boundary conditions at the string scale of about $2 \times 10^{17}$ GeV, including the supersymmetry breaking $B_μ$ parameter which is strictly enforced as $B_μ = 0$. Given the proportional dependence of all model scales on a single parameter $M_{1/2}$, No-Scale $\cal{F}$-$SU$(5) was shown to possess no electroweak fine-tuning and thus persists as a $natural$ one-parameter model. In this fresh analysis here, we demand consistency with the measured 125 GeV light Higgs boson mass, though we forgo an upper limit on the lightest neutralino relic density. The resulting phenomenology delivers a gluino mass of $M(\widetilde{g}) \lesssim 7.5$ TeV and a lightest supersymmetric particle (LSP) of $M(\widetildeχ_1^0) \lesssim 1.6$ TeV. In order to dilute the relic density down to the WMAP and Planck measurements, we rely upon a single cosmological master coupling $λ_6$.

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arXiv2019

Naturalness in D-brane Inspired Models

We examine the naturalness of the D-brane inspired model constructed in flipped $SU(5)$ supplemented with vector-like particles at the TeV scale, dubbed flippons. We find the model can produce a mainly Higgsino-like lightest supersymmetric particle (LSP) and small light stops, as favored by naturalness. In fact, a large trilinear scalar $A_t$ term at the electroweak (EW) scale creates a large mass splitting between the top squarks, driving the light stop to near degeneracy with an LSP that is almost all Higgsino, with $ΔM(\widetilde{t}_1, \widetildeχ_1^0) < 5$ GeV, evading the LHC constraint on $\widetilde{t}_1 \to c \widetildeχ_1^0$ thus far. Given the smallness of the light stop, generating a 125 GeV light Higgs boson mass is aided by one-loop contributions from the Yukawa couplings between the flippons and Higgs fields. The resulting parameter space satisfying naturalness is rather constrained, thus we assess its viability by means of comparison to the LHC constraint on soft charm jets and direction detection limits on spin-independent cross-sections. Finally, we compute the level of electroweak fine-tuning and uncover a region with $Δ_{EW} < 30$, $i.e.$, fine-tuning better than 3%, regarded as low electroweak fine-tuning. Given the small light stop, the electroweak fine-tuning from only the top squarks is of $\cal{O}$(1), indicating no fine-tuning from neither the light stop $\widetilde{t}_1$ nor the heavy stop $\widetilde{t}_2$.

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arXiv2018

Inspiration from Intersecting D-branes: General Supersymmetry Breaking Soft Terms in No-Scale ${\cal F}$-$SU(5)$

Motivated by D-brane model building, we evaluate the $\cal{F}$-$SU(5)$ model with additional vector-like particle multiplets, referred to as flippons, within the framework of No-Scale Supergravity with non-vanishing general supersymmetry breaking soft terms at the string scale. The viable phenomenology is uncovered by applying all current experimental constraints, including but not limited to the correct light Higgs boson mass, WMAP and Planck relic density measurements, and several LHC constraints on supersymmetric particle spectra. Four interesting regions of the parameter space arise, as well as mixed scenarios, given by: (i) light stop coannihilation; (ii) pure Higgsino dark matter; (iii) Higgs funnel; and (iv) light stau coannihilation. All regions can generate the observed value of the relic density commensurate with a 125 GeV light Higgs boson mass, with the exception of the relatively small relic density value for the pure Higgsino lightest supersymmetric particle (LSP). This work is concluded by gauging the model against present LHC search constraints and derivation of the final states observable at the LHC for each of these scenarios.

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arXiv2017

Probing the No-Scale ${\cal F}$-$SU(5)$ One-Parameter Model via Gluino Searches at the LHC2

In our recent paper entitled "The return of the King: No-Scale ${\cal F}$-$SU(5)$", we showed that the model space supporting the most favorable phenomenology should have been probed in 2016 at the LHC2, with an even further reach into this region of the model in 2017-18. This ideal realm of the one-parameter version of No-Scale ${\cal F}$-$SU(5)$ yields a 1.9-2.3 TeV gluino mass at the very same point where the light Higgs boson mass enters its rather narrow experimentally determined range of $m_h = 125.09 \pm 0.24$ GeV. Given the recent results reported at Moriond 2017 for 36 ${\rm fb}^{-1}$ of luminosity collected in 2016 at the 13 TeV LHC2, we now update the status of the No-Scale ${\cal F}$-$SU(5)$ model space in light of the gluino mass exclusion limits presented by the ATLAS and CMS Collaborations. We illustrate that a resolution could be reached soon as to whether supersymmetry lives in this most critical region of the model space.

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arXiv2017

General No-Scale Supergravity: An ${\cal F}$-$SU(5)$ Tale

We study the grand unification model flipped $SU(5)$ with additional vector-like particle multiplets, or ${\cal F}$-$SU(5)$ for short, in the framework of General No-Scale Supergravity. In our analysis we allow the supersymmetry (SUSY) breaking soft terms to be generically non-zero, thereby extending the phenomenologically viable parameter space beyond the highly constrained one-parameter version of ${\cal F}$-$SU(5)$. In this initial inquiry, the mSUGRA/CMSSM SUSY breaking terms are implemented. We find this easing away from the vanishing SUSY breaking terms enables a more broad mass range of vector-like particles, dubbed flippons, including flippons less than 1 TeV that could presently be observed at the LHC2, as well as a lighter gluino mass and SUSY spectrum overall. This presents heightened odds that the General No-Scale ${\cal F}$-$SU(5)$ viable parameter space can be probed at the LHC2. The phenomenology comprises both bino and higgsino dark matter, including a Higgs funnel region. Particle states emerging from the SUSY cascade decays are presented to experimentally distinguish amongst the diverse phenomenological regions.

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arXiv2016

The Return of the King: No-Scale ${\cal F}$-$SU(5)$

We revisit the viable parameter space in No-Scale ${\cal F}$-$SU(5)$, examining the Grand Unified Theory within the context of the prevailing gluino mass limits established by the LHC. The satisfaction of both the No-Scale boundary condition and the experimentally measured Standard Model (SM) like Higgs boson mass requires a lower limit on the gluino mass in the model space of about 1.9 TeV, which maybe not coincidentally is the current LHC supersymmetry search bound. This offers a plausible explanation as to why a supersymmetry signal has thus far not been observed at the LHC. On the contrary, since the vector-like flippon particles are relatively heavy due to the strict condition that the supersymmetry breaking soft term $B_μ$ must vanish at the unification scale, we also cannot address the recently vanished 750 GeV diphoton resonance at the 13 TeV LHC. Therefore, No-Scale ${\cal F}$-$SU(5)$ returns as a King after the spurious 750 GeV diphoton excess was gone with the wind.

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arXiv2016

A Flippon Related Singlet at the LHC II

We consider the 750 GeV diphoton resonance at the 13 TeV LHC in the ${\cal F}$-$SU(5)$ model with a Standard Model (SM) singlet field which couples to TeV-scale vector-like particles, dubbed $flippons$. This singlet field assumes the role of the 750 GeV resonance, with production via gluon fusion and subsequent decay to a diphoton via the vector-like particle loops. We present a numerical analysis showing that the observed 8 TeV and 13 TeV diphoton production cross-sections can be generated in the model space with realistic electric charges and Yukawa couplings for light vector-like masses. We further discuss the experimental viability of light vector-like masses in a General No-Scale ${\cal F}$-$SU(5)$ model, offering a few benchmark scenarios in this consistent GUT that can satisfy all experimental constraints imposed by the LHC and other essential experiments.

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arXiv2016

The $750$ GeV Diphoton Excesses in a Realistic D-brane Model

We study the diphoton excesses near $750$ GeV recently reported by the ATLAS and CMS collaborations within the context of a phenomenologically interesting intersecting/magnetized D-brane model on a toroidal orientifold. It is shown that the model contains a SM singlet scalar as well as vector-like quarks and leptons. In addition, it is shown that the singlet scalar has Yukawa couplings with vector-like quarks and leptons such that it may be produced in proton-proton collisions via gluon fusion as well as decay to diphotons through loops involving the vector-like quarks. Moreover, the required vector-like quarks and leptons may appear in complete $SU(5)$ multiplets so that gauge coupling unification may be maintained. Finally, it is shown that the diphoton signal may be explained within the model.

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arXiv2016

The Diboson Excesses in Leptophobic $U(1)_{\rm LP}$ Models from String Theories

The ATLAS Collaboration has reported excesses in the search for resonant diboson production with decay modes to hadronic final states at a diboson invariant mass around 2 TeV in boosted jets from $WZ$, $W^+W^-$, and $ZZ$ channels. Given potential contamination, we investigate the anomalies in leptophobic $U(1)_{\rm LP}$ models. We show that leptophobic models can be constructed in flipped $SU(5)\times U(1)_X$ models from free fermionic string constructions and Pati-Salam models from D-brane constructions. Additionally, we perform a collider phenomenological analysis to study production cross sections for $pp \to Z' \to jj/t \bar{t}/WW/Zh$ and discover the excess can be interpreted in both the leptophobic flipped $SU(5)\times U(1)_X$ models and intersecting D-branes.

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arXiv2015

The 14 TeV LHC Takes Aim at SUSY: A No-Scale Supergravity Model for LHC Run 2

The Supergravity model named No-Scale ${\cal F}$-$SU(5)$, which is based upon the flipped $SU$(5) Grand Unified Theory (GUT) with additional TeV-scale vector-like flippon multiplets, has been partially probed during the LHC Run 1 at 7-8 TeV, though the majority of its model space remains viable and should be accessible by the 13-14 TeV LHC during Run 2. The model framework possesses the rather unique capacity to provide a light CP-even Higgs boson mass in the favored 124-126 GeV window while simultaneously retaining a testably light supersymmetry (SUSY) spectrum. We summarize the outlook for No-Scale ${\cal F}$-$SU(5)$ at the 13-14 TeV LHC and review a promising methodology for the discrimination of its long-chain cascade decay signature. We further show that proportional dependence of all model scales upon the unified gaugino mass $M_{1/2}$ minimizes electroweak fine-tuning, allowing the $Z$-boson mass $M_Z$ to be expressed as an explicit function of $M_{1/2}$, $M_Z^2 = M_Z^2 (M_{1/2}^2)$, with implicit dependence upon a dimensionless ratio $c$ of the supersymmetric Higgs mixing parameter $μ$ and $M_{1/2}$. Finally, we elucidate an empirical connection between recent scalar tensor measurements and No-Scale Supergravity cosmological models that mimic the Starobinsky model of inflation.

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arXiv2014

Third Generation in Cascade Decays

In supersymmetric models with gluinos around 1000-2000 GeV, new physics searches based on cascade decay products of the gluino are viable at the next run of the LHC. We investigate a scenario where the light stop is lighter than the gluino and both are lighter than all other squarks, and show that its signal can be established using multi b-jet, multi W and/or multi lepton final state topologies. We then utilize both boosted and conventional jet topologies in the final state in conjunction with di-tau production as a probe of the stau-neutralino co-annihilation region responsible for the model's dark matter content. This study is performed in the specific context of one such phenomenologically viable model named No-Scale F-SU(5).

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arXiv2014

Confronting Electroweak Fine-tuning with No-Scale Supergravity

Applying No-Scale Supergravity boundary conditions at a heavy unification scale to the Flipped $SU(5)$ grand unified theory with extra TeV-scale vector-like multiplets, $i.e.$ No-Scale ${\cal F}$-$SU(5)$, we express the $Z$-boson mass $M_Z$ as an explicit function of the boundary gaugino mass $M_{1/2}$, $M_Z^2 = M_Z^2 (M_{1/2}^2)$, with implicit dependence upon a dimensionless ratio $c$ of the supersymmetric Higgs mixing parameter $μ$ and $M_{1/2}$. Setting the top Yukawa coupling consistent with $m_t = 174.3$ GeV at $M_Z = 91.2$ GeV, the value of $c$ naturally tends toward $c \simeq 1$, which indirectly suggests underlying action of the Giudice-Masiero mechanism. Proportional dependence of all model scales upon the unified gaugino mass $M_{1/2}$ in the No-Scale ${\cal F}$-$SU(5)$ model suggests one possible mechanism of confronting the electroweak fine tuning problem.

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arXiv2014

No Naturalness or Fine-tuning Problems from No-Scale Supergravity

We compute the electroweak fine-tuning in No-Scale Supergravity for a representative supersymmetric Grand Unification Theory (GUT) model, flipped $SU(5)$ with extra vector-like $flippons$, dubbed $\cal{F}$-$SU(5)$. We find that there is no problematic electroweak fine-tuning in No-Scale $\cal{F}$-$SU(5)$, due to an elegant proportional rescaling of the full mass spectrum with respect to just the unified gaugino mass $M_{1/2}$, as well as a dynamic equivalence enforced between $M_{1/2}$ and the supersymmetric Higgs mixing parameter $μ$ at the heavy unification scale. We demonstrate both analytically and numerically that the No-Scale $\cal{F}$-$SU(5)$ fine-tuning parameter is consequently of unit order, $Δ_{\rm EENZ} \simeq {\cal O}(1)$, at the electroweak scale.

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arXiv2014

Testing No-Scale Supergravity with the Fermi Space Telescope LAT

We describe a methodology for testing No-Scale Supergravity by the LAT instrument onboard the Fermi Space Telescope via observation of gamma ray emissions from lightest supersymmetric (SUSY) neutralino annihilations. For our test vehicle we engage the framework of the supersymmetric grand unified model No-Scale Flipped $SU(5)$ with extra vector-like flippon multiplets derived from F-Theory, known as $\cal{F}$-$SU(5)$. We show that through compression of the light stau and light bino neutralino mass difference, where internal bremsstrahlung (IB) photons give a dominant contribution, the photon yield from annihilation of SUSY dark matter can be elevated to a number of events potentially observable by the Fermi-LAT in the coming years. Likewise, the increased yield in No-Scale $\cal{F}$-$SU(5)$ may also have rendered the existing observation of a 133 GeV monochromatic gamma ray line visible, if additional data should exclude systematic or statistical explanations. The question of intensity aside, No-Scale $\cal{F}$-$SU(5)$ can indeed provide a natural weakly interacting massive particle (WIMP) candidate with a mass in the correct range to yield $γγ$ and $γZ$ emission lines at $m_χ \sim 133$ GeV and $m_χ \sim 145$ GeV, respectively. Additionally, we elucidate the emerging empirical connection between recent Planck satellite data and No-Scale Supergravity cosmological models which mimic the Starobinsky model of inflation. Together, these experiments furnish rich alternate avenues for testing No-Scale $\cal{F}$-$SU(5)$, and similarly structured models, the results of which may lend independent credence to observations made at the LHC.

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