arXiv subjects

Hyun Min Lee

Publications and source records attributed to Hyun Min Lee.

At least 91 records · Page 5Linked to original sources

arXiv2017

KK graviton resonance and cascade decays in warped gravity

We consider the Kaluza-Klein (KK) graviton and its decays in the presence of the light radion, the modulus of extra dimension, appearing naturally light due to classical scale invariance in warped gravity. Due to the presence of a sizable wavefunction overlap in the extra dimension between the KK graviton and the radion, the KK graviton can decay largely into a pair of radions, each of which decays into a pair of collimated photons or photon-jets. Focusing on the setup where the KK graviton has suppressed couplings to the Higgs boson and fermions, we discuss the bounds on the light radion in the parameter space where the photon-jets are relevant. Moreover, we pursue the possibility of distinguishing the scenario from the case with direct photon contributions by the angular distributions of photons in the LHC Run 2. Roles of KK graviton and radion as mediators of dark matter interactions, extensions with brane kinetic terms and the model with a holographic composite Higgs are also addressed.

hep-ph↗

arXiv2017

SIMP dark matter and its cosmic abundances

We give a review on the thermal average of the annihilation cross-sections for $3\rightarrow 2$ and general higher-order processes. Thermal average of higher order annihilations highly depend on the velocity of dark matter, especially, for the case with resonance poles. We show such examples for scalar dark matter in gauged $Z_3$ models.

hep-ph↗

arXiv2017

Forbidden Channels and SIMP Dark Matter

In this review, we focus on dark matter production from thermal freeze-out with forbidden channels and SIMP processes. We show that forbidden channels can be dominant to produce dark matter depending on the dark photon and / or dark Higgs mass compared to SIMP.

hep-ph↗

arXiv2017

Flattening the inflaton potential beyond minimal gravity

We review the status of the Starobinsky-like models for inflation beyond minimal gravity and discuss the unitarity problem due to the presence of a large non-minimal gravity coupling. We show that the induced gravity models allow for a self-consistent description of inflation and discuss the implications of the inflaton couplings to the Higgs field in the Standard Model.

hep-ph↗

arXiv2017

Wilson lines and UV sensitivity in magnetic compactifications

We investigate the ultraviolet (UV) behaviour of 6D N=1 supersymmetric effective (Abelian) gauge theories compactified on a two-torus ($T_2$) with magnetic flux. To this purpose we compute offshell the one-loop correction to the Wilson line state self-energy. The offshell calculation is actually necessary to capture the usual effective field theory expansion in powers of $(\partial/Λ)$. Particular care is paid to the regularization of the (divergent) momentum integrals, which is relevant for identifying the corresponding counterterm(s). We find a counterterm which is a new higher dimensional effective operator of dimension d=6, that is enhanced for a larger compactification area (where the effective theory applies) and is consistent with the symmetries of the theory. Its consequences are briefly discussed and comparison is made with orbifold compactifications without flux.

hep-th↗

arXiv2017

Cosmic abundances of SIMP dark matter

Thermal production of light dark matter with sub-GeV scale mass can be attributed to $3\rightarrow 2$ self-annihilation processes. We consider the thermal average for annihilation cross sections of dark matter at $3\rightarrow 2$ and general higher-order interactions. A correct thermal average for initial dark matter particles is important, in particular, for annihilation cross sections with overall velocity dependence and/or resonance poles. We apply our general results to benchmark models for SIMP dark matter and discuss the effects of the resonance pole in determining the relic density.

hep-ph↗

arXiv2016

On thermal production of self-interacting dark matter

We consider thermal production mechanisms of self-interacting dark matter in models with gauged $Z_3$ symmetry. A complex scalar dark matter is stabilized by the $Z_3$, that is the remnant of a local dark $U(1)_d$. Light dark matter with large self-interaction can be produced from thermal freeze-out in the presence of SM-annihilation, SIMP and/or forbidden channels. We show that dark photon and/or dark Higgs should be relatively light for unitarity and then assist the thermal freeze-out. We identify the constraints on the parameter space of dark matter self-interaction and mass in cases that one or some of the channels are important in determining the relic density.

hep-ph↗

arXiv2016

Bounds on supersymmetric effective operators from heavy diphoton searches

We identify the bounds on supersymmetric effective operators beyond MSSM, from heavy diphoton resonance ($X$) negative searches at the LHC, where $X$ is identified with the neutral CP-even (odd) $H$ ($A$) or both (mass degenerate). While minimal supersymmetric models (MSSM, etc) comply with the data, a leading effective operator of $d=6$ can contribute significantly to diphoton production $σ\sim 1$ fb, well above its MSSM value and in conflict with recent data. Both the $b\bar b$ and $gg$ production mechanisms of $H$ and $A$ can contribute comparably to this. We examine the dependence of the diphoton cross section $σ$ on the values of $m_X$, $Λ$ and $\tanβ$, under the experimental constraints from the SM-like higgs couplings $hgg$ and $hγγ$ (due to mixing) and from the $b\bar b$ and $t\bar t$ searches. These give $Λ$ larger than $\sim 5$ TeV for $m_X$ in the range $0.5-1$ TeV. We show how to generate the $d=6$ effective operator from microscopic (renormalizable) models. This demands the presence of vector-like states beyond the MSSM spectrum (and eventually but not necessarily a gauge singlet), of mass near $Λ$ and thus outside the LHC reach.

hep-ph↗

arXiv2016

Diphoton resonance confronts dark matter

As an interpretation of the 750 GeV diphoton excesses recently reported by both ATLAS and CMS collaborations, we consider a simple extension of the Standard Model with a Dirac fermion dark matter where a singlet complex scalar field mediates between dark matter and SM particles via effective couplings to SM gauge bosons and/or Higgs-portal. In this model, we can accommodate the diphoton events through the direct and/or cascade decays of pseudo-scalar and real scalar partners of the complex scalar field. We show that mono-jet searches and gamma-ray observations are complementary in constraining the region where the width of the diphoton resonance can be enhanced due to the couplings of the resonance to dark matter and the correct relic density is obtained. In the case of cascade decay of the resonance, the effective couplings of singlet scalars can be smaller, but the model is still testable by the future discrimination between single photon and photon-jet at the LHC as well as the gamma-ray searches for the cascade annihilation of dark matter.

hep-ph↗

arXiv2016

Inflection point inflation and reheating

We revisit the inflection point inflation with an extended discussion to large field values and consider the reheating effects on the inflationary predictions. Parametrizing the reheating dynamics in terms of the reheating temperature and the equation of state during inflation, we show how the observationally favored parameter space of inflection point inflation is affected by reheating dynamics. Consequently, we apply the general results to the inflation models with non-minimal coupling, such as the SM Higgs inflation and the $B-L$ Higgs inflation.

hep-ph↗

arXiv2016

Gamma-ray boxes from axion-mediated dark matter

We compute the gamma-ray output of axion-mediated dark matter and derive the corresponding constraints set by recent data. In such scenarios the dark matter candidate is a Dirac fermion that pair-annihilates into axions and/or scalars. Provided that the axion decays (at least partly) into photons, these models naturally give rise to a box-shaped gamma-ray spectrum that may present two distinct phenomenological behaviours: a narrow box, resembling a line at half the dark matter mass, or a wide box, spanning an extensive energy range up to the dark matter mass. Remarkably, we find that in both cases a sizable gamma-ray flux is predicted for a thermal relic without fine-tuning the model parameters nor invoking boost factors. This large output is in line with recent Fermi-LAT observations towards the Galactic centre region and is on the verge of being excluded. We then make use of the Fermi-LAT and H.E.S.S. data to derive robust, model-independent upper limits on the dark matter annihilation cross section for the narrow and wide box scenarios. H.E.S.S. constraints, in particular, turn out to match the ones from Fermi-LAT at hundreds of GeV and extend to multi-TeV masses. Future Cherenkov telescopes will likely probe gamma-ray boxes from thermal dark matter relics in the whole multi-TeV range, a region hardly accessible to direct detection, collider searches and other indirect detection strategies.

hep-ph↗

arXiv2016

The diphoton resonance as a gravity mediator of dark matter

We consider the possibility of interpreting the recently reported diphoton excess at 750 GeV as a spin-two massive particle (such as a Kaluza-Klein graviton in warped extra-dimensions) which serves as a mediator to Dark Matter via its gravitational couplings to the dark sector and to the Standard Model (SM). We model non-universal couplings of the resonance to gauge bosons in the SM and to Dark Matter as a function on their localization in the extra dimension. We find that scalar, fermion or vector dark matter can saturate the dark matter relic density by the annihilation of dark matter into a pair of the SM particles or heavy resonances, in agreement with the diphoton resonance signal strength. We check the compatibility of our hypothesis with other searches for the KK graviton. We show that the invisible decay rate of the resonance into a pair of dark matter is subdominant in the region of the correct relic density, hence leading to no constraints from the mono-jet bound at 8 TeV via the gluon coupling. We also discuss the kinematic features of the decay products of a KK graviton to distinguish the KK graviton from the SM backgrounds or a scalar particle interpretation of the diphoton resonance.

hep-ph↗

arXiv2016

Resonant SIMP dark matter

We consider a resonant SIMP dark matter in models with two singlet complex scalar fields charged under a local dark $U(1)_D$. After the $U(1)_D$ is broken down to a $Z_5$ discrete subgroup, the lighter scalar field becomes a SIMP dark matter which has the enhanced $3\rightarrow 2$ annihilation cross section near the resonance of the heavier scalar field. Bounds on the SIMP self-scattering cross section and the relic density can be fulfilled at the same time for perturbative couplings of SIMP. A small gauge kinetic mixing between the SM hypercharge and dark gauge bosons can be used to make SIMP dark matter in kinetic equilibrium with the SM during freeze-out.

hep-ph↗

arXiv2016

Reheating the Universe at Criticality

We present the general discussion on the inflection point inflation with small or large inflaton fields and show the effects of reheating dynamics on the inflationary predictions. In order to compare the model predictions with precisely measured CMB anisotropies and constrain the inflation models, the knowledge of the reheating dynamics is required. Inflection point inflation extended to the trans-Planckian regime can accommodate a sizable tensor-to-scalar ratio at the detectable level in the future CMB experiments.

hep-ph↗

arXiv2015

Models for SIMP dark matter and dark photon

We give a review on the SIMP paradigm and discuss a consistent model for SIMP dark mesons in the context of a dark QCD with flavor symmetry. The $Z'$-portal interaction is introduced being compatible with stable dark mesons and is responsible for making the SIMP dark mesons remain in kinetic equilibrium with the SM during the freeze-out process. The SIMP parameter space of the $Z'$ gauge boson can be probed by future collider and direct detection experiments.

hep-ph↗

arXiv2015

Diboson Excesses Demystified in Effective Field Theory Approach

We study the collider implication of a neutral resonance which decays to several diboson final states such as $W^+W^-$, $ZZ$, and $Zγ$ via a minimal set of effective operators. We consider both CP-even and CP-odd bosonic states with spin 0, 1, or 2. The production cross sections for the bosonic resonance states are obtained with the effective operators involving gluons (and quarks), and the branching fractions are obtained with the operators responsible for the interactions with electroweak gauge bosons. We demonstrate that each scenario allows for a broad parameter space which could accommodate the recently-reported intriguing excesses in the ATLAS diboson final states, and discuss how the CP states and spin information of the resonance can be extracted at the LHC run II.

hep-ph↗

arXiv2015

SIMP dark matter with gauged $Z_3$ symmetry

We consider a complex scalar field as SIMP dark matter in models with gauged $Z_3$ discrete symmetry appearing as a remnant of dark local $U(1)$. Dark matter (DM) annihilates dominantly by the 3-to-2 scattering, due to the DM cubic coupling in combination with the DM quartic coupling or the $Z'$ gauge and dark Higgs couplings. We show that a light $Z'$ gauge boson makes DM in kinetic equilibrium with thermal plasma at freeze-out and it affects the DM relic density and perturbativity/unitarity constraints for DM self-interactions. We show that the large DM self-interactions are consistent with solving small-scale structure problems and explaining the DM halo separation recently observed in Abell 3827 cluster. Various bounds on the model from the SIMP conditions, DM self-interactions, $Z'$ searches, DM direct/indirect detection experiments, and Higgs signals, are also discussed.

hep-ph↗

arXiv2015

Communication with SIMP dark mesons via Z'-portal

We consider a consistent extension of the SIMP models with dark mesons by including a dark U(1)_D gauge symmetry. Dark matter density is determined by a thermal freeze-out of the $3\to2$ self-annihilation process, thanks to the Wess-Zumino-Witten term. In the presence of a gauge kinetic mixing between the dark photon and the SM hypercharge gauge boson, dark mesons can undergo a sufficient scattering off the Standard Model particles and keep in kinetic equilibrium until freeze-out in this SIMP scenario. Taking the SU(N_f)xSU(N_f)/SU(N_f) flavor symmetry under the SU(N_c) confining group, we show how much complementary the SIMP constraints on the parameters of the dark photon are for current experimental searches for dark photon.

hep-ph↗