Research

Research Interests

Theoretical High Energy Physics and Particle Physics
- Conformal Supergravity
- Engineering of Scalar Field Dynamics and Particle Physics in 4D N=1 Supergravity
- String/Brane Dynamics, Swampland Conjectures, Double Field Theory
- Symmetries, Gaugings, Topological Field Theories
- Operator Algebras
Gravitation and Cosmology,
- Inflationary Attractors, Reheating
- Modified Gravity (e.g. Horndeski), Gravitational Waves
- Exotic Astrophysical Objects: Wormholes, Black Holes, and Neutron Stars
Mathematical Physics
- Construction of new geometrical/algebraic structures and its application to theoretical high energy physics

Research Projects for Undergraduates

TBA

Research Papers [8]

A propagating chiral string

Traversable Wormhole for String, but not for Particle (2024)

Hun Jang, Minkyoo Kim, Hocheol Lee, and Jeong-Hyuck Park
arXiv:2412.04128 [hep-th], review-completed in Physics Letters B (PLB).

We propose a novel Lorentzian wormhole geometry that exhibits fundamentally different behavior for strings versus point particles. The geometry features a closed string massless sector with nontrivial H-flux and a scalar dilaton with negative kinetic term in the string frame. Our three-region geometry contains a throat in the middle region, with boundaries forming non-Riemannian two-spheres where fundamental strings become chiral. Key finding: While point particles cannot traverse between regions, chiral strings can traverse freely, demonstrating a fundamental difference in how extended objects versus point particles experience curved spacetime.

Supermassive Gauginos in Supergravity Inflation with High-Scale SUSY Breaking (2024)

Hun Jang and Massimo Porrati
JHEP 08 (2024) 019 | arXiv:2405.00551 [hep-th]

We solve a critical problem in supergravity inflation models where gauginos remained massless due to exact F-term cancellations. Our model achieves slow-roll inflation without F-term SUSY breaking, using only D-term breaking via new Fayet-Iliopoulos terms. Innovation: We introduce a new F-term that becomes singular in the supersymmetric limit, successfully generating large gaugino masses while preserving the spectrum of other particles and maintaining the theory's cutoff scale.

Gauge Theory on Fiber Bundle of Hypercomplex Algebras (2023)

Hun Jang
Nuclear Physics B 993 (2023) 116281 | arXiv:2303.08159 [hep-th]

This work addresses the fundamental vacuum selection problem: how nature chooses one vacuum among degenerate physical states. We construct novel gauge theories on fiber bundles with hypercomplex algebra fibers, discovering an impenetrable domain wall that prevents phase transitions between vacua. Key result: Dynamic vacuum selection occurs due to intrinsic even parity of scalar fields under ℤ₂ symmetry, even when the potential itself is ℤ₂-symmetric, providing a mechanism for spontaneous vacuum selection.

Realization of Slow Roll Inflation and the MSSM (2022)

Hun Jang and Massimo Porrati
Physical Review D 106, 045024 (2022) | arXiv:2207.01889 [hep-th]

We demonstrate how to connect inflationary cosmology with particle physics by constructing a supergravity model that realizes both slow-roll inflation and the Minimal Supersymmetric Standard Model. Using generalized new D-terms, we achieve high-scale SUSY breaking with gravity mediation while giving appropriate masses to superpartners. Theoretical proof: We establish that the cutoff of effective theories with new D-terms never exceeds the supersymmetry breaking scale.

Relaxed Supergravity (2021)

Hun Jang
arXiv:2112.02464 [hep-th]

We introduce "Relaxed Supergravity," a revolutionary extension of N=1 supergravity that dramatically expands the space of allowed scalar potentials. Breakthrough discovery: We identify the first new negative-definite contribution to scalar potentials in both supergravity and global SUSY, beyond the traditional gravitino-mass term. This relaxes fundamental constraints that have limited supergravity model building for decades, opening new possibilities for phenomenological applications.

Component Actions of Liberated N=1 Supergravity (2021)

Hun Jang and Massimo Porrati
JHEP 11 (2021) 075 | arXiv:2108.04469 [hep-th]

We provide the complete component field formulation for "Liberated Supergravity" theories using superconformal tensor calculus. These theories feature enlarged scalar potential spaces and fermionic interactions that become singular in the unbroken SUSY limit. Technical contribution: Explicit derivation of field equations and new Kähler-invariant Fayet-Iliopoulos terms, complementing our earlier constraint analysis with full computational details.

Inflation, Gravity Mediated SUSY Breaking, and de Sitter Vacua (2021)

Hun Jang and Massimo Porrati
Physical Review D 103, 105006 (2021) | arXiv:2102.11358 [hep-th]

We tackle the notoriously difficult problem of constructing stable de Sitter vacua in supergravity. Using Kähler-invariant Fayet-Iliopoulos terms, we show how to simultaneously achieve inflationary dynamics and gravity-mediated supersymmetry breaking while maintaining mathematical consistency—a longstanding challenge in the field.

Constraining Liberated Supergravity (2021)

Hun Jang and Massimo Porrati
Physical Review D 103, 025008 (2021) | arXiv:2010.06789 [hep-th]

We establish the theoretical foundations and fundamental limits of liberated supergravity theories. Key findings: These effective theories have intrinsic cutoffs determined by nonrenormalizable fermionic interactions. While the new terms cannot produce observable changes to the cosmological constant or particle masses under current bounds, we demonstrate viable slow-roll inflation models that operate well above the Hubble scale during inflation.

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