arXiv subjects

Jinsu Kim

Publications and source records attributed to Jinsu Kim.

At least 73 records · Page 4Linked to original sources

arXiv2019

Exploiting higher-order resonant modes for axion haloscopes

The haloscope is one of the most sensitive approaches to the QCD axion physics within the region where the axion is considered to be a dark matter candidate. Current experimental sensitivities, which rely on the lowest fundamental TM010 mode of a cylindrical cavity, are limited to relatively low mass regions. Exploiting higher-order resonant modes would be beneficial because it will enable us to extend the search range with no volume loss and higher quality factors. This approach has been discarded mainly because of the significant degradation of form factor, and difficulty with frequency tuning. Here we introduce a new tuning mechanism concept which both enhances the form factor and yields reasonable frequency tunability. A proof of concept demonstration verified that this design is feasible for high mass axion search experiments.

physics.ins-det↗

arXiv2019

Axion Dark Matter Research with IBS/CAPP

The axion, a consequence of the PQ mechanism, has been considered as the most elegant solution to the strong-CP problem and a compelling candidate for cold dark matter. The Center for Axion and Precision Physics Research (CAPP) of the Institute for Basic Science (IBS) was established on 16 October 2013 with a main objective to launch state of the art axion experiments in South Korea. Relying on the haloscope technique, our strategy is to run several experiments in parallel to explore a wide range of axion masses with sensitivities better than the QCD axion models. We utilize not only the advanced technologies, such as high-field large-volume superconducting (SC) magnets, ultra low temperature dilution refrigerators, and nearly quantum-limited noise amplifiers, but also some unique features solely developed at the Center, including high-quality SC resonant cavities surviving high magnetic fields and efficient cavity geometries to reach high-frequency regions. Our goal is to probe axion dark matter in the frequency range of 1-10 GHz in the first phase and then ultimately up to 25 GHz, even in a scenario where axions constitute only 10% of the local dark matter halo. In this report, the current status and future prospects of the experiments and R&D activities at IBS/CAPP are described.

physics.ins-det↗

arXiv2019

Tier structure of strongly endotactic reaction networks

Reaction networks are mainly used to model the time-evolution of molecules of interacting chemical species. Stochastic models are typically used when the counts of the molecules are low, whereas deterministic models are used when the counts are in high abundance. In 2011, the notion of `tiers' was introduced to study the long time behavior of deterministically modeled reaction networks that are weakly reversible and have a single linkage class. This `tier' based argument was analytical in nature. Later, in 2014, the notion of a strongly endotactic network was introduced in order to generalize the previous results from weakly reversible networks with a single linkage class to this wider family of networks. The point of view of this later work was more geometric and algebraic in nature. The notion of strongly endotactic networks was later used in 2018 to prove a large deviation principle for a class of stochastically modeled reaction networks. We provide an analytical characterization of strongly endotactic networks in terms of tier structures. By doing so, we shed light on the connection between the two points of view, and also make available a new proof technique for the study of strongly endotactic networks. We show the power of this new technique in two distinct ways. First, we demonstrate how the main previous results related to strongly endotactic networks, both for the deterministic and stochastic modeling choices, can be quickly obtained from our characterization. Second, we demonstrate how new results can be obtained by proving that a sub-class of strongly endotactic networks, when modeled stochastically, is positive recurrent. Finally, and similarly to recent independent work by Agazzi and Mattingly, we provide an example which closes a conjecture in the negative by showing that stochastically modeled strongly endotactic networks can be transient (and even explosive).

math.PR↗

arXiv2019

Searching for Flavored Gauge Bosons

Standard Model may allow an extended gauge sector with anomaly-free flavored gauge symmetries, such as $L_{i} - L_{j}$, $B_{i} - L_{j}$, and $B - 3L_{i}$, where $i,j=1,2,3$ are flavor indices. We investigate phenomenological implications of the new flavored gauge boson $Z^{\prime}$ in the above three classes of gauge symmetries. Focusing on the gauge boson mass above 5 GeV, we use the lepton universality test in the $Z$ and $τ/μ$ decays, LEP searches, LHC searches, neutrino trident production bound, and LHC $Z\rightarrow 4μ$ searches to put constraints on the $g^{\prime}-M_{Z^{\prime}}$ plane. When $L_1$ is involved, the LEP bounds on the $e^{-}e^{+} \rightarrow \ell^{-}\ell^{+}$ processes give the most stringent bounds, while the LHC bound becomes the strongest constraints in the large $M_{Z^{\prime}}$ region when $B_{i}$ is involved. The bound from $Z\rightarrow 4μ$ productions, which is applicable for $L_2$-involved scenarios, provides stringent bounds in the small $M_{Z^{\prime}}$ region. One exception is the $B-3L_2$ scenario, in which case only a small region is favored due to the lepton universality.

hep-ph↗

arXiv2019

Revealing electrically undetectable room temperature surface-mobility of bulky topological insulators by spectroscopic techniques

High surface-mobility, which is attributable to topological protection, is a trademark of three-dimensional topological insulators (3DTIs). Exploiting surface-mobility indicates successful application of topological properties for practical purposes. However, the detection of the surface-mobility has been hindered by the inevitable bulk conduction. Even in the case of high-quality crystals, the bulk state forms the dominant channel of the electrical current. Therefore, with electrical transport measurement, the surface-mobility can be resolved only below-micrometer-thick crystals. The evaluation of the surface-mobility becomes more challenging at higher temperatures, where phonons can play a role. Here, using spectroscopic techniques, we successfully evaluated the surface-mobility of Bi2Te3 (BT) at room temperature (RT). We acquired the effective masses and mean scattering times for both the surface and bulk states using angle-resolved photoemission and terahertz time-domain spectroscopy. We revealed a record-high surface-mobility for BT, exceeding 33,000 cm^2/(Vs) per surface sheet, despite intrinsic limitations by the coexisting bulk state as well as phonons at RT. Our findings partially support the interesting conclusion that the topological protection persists at RT. Our approach could be applicable to other topological materials possessing multiband structures near the Fermi level.

cond-mat.mes-hall↗

arXiv2019

Effective Approximation of Electromagnetism for Axion Haloscope Searches

We applied an effective approximation into Maxwell's equations with an axion interaction for haloscope searches. A set of Maxwell's equations acquired from this approximation describes just the reacted fields generated by the anomalous interaction. Unlike other approaches, this set of Maxwell's equations inherently satisfies the boundary conditions for haloscope searches. The electromagnetic field solutions from the Maxwell's equations were evaluated for both cylindrical and toroidal cavity geometries including when the axion mass becomes ultra-light (sub-meV). A small but non-zero difference between the electric and magnetic stored energies appeared in both cases. The difference may come from an anomalous non-dissipating current induced by oscillating axions.

hep-ph↗

arXiv2018

Comment on "Tunable Supermode Dielectric Resonators for Axion Dark-Matter Haloscopes"

We comment on a recently published paper, Phys. Rev. Applied 9, 014028 (2018), which presents frequency-tuning mechanisms for dielectric resonators and demonstrates their potential application to axion haloscopes. One of the schemes introduces a cylindrical dielectric hollow and splits it in the axial direction to tune the frequency. The authors claim that this scheme offers a 1 to 2-order-of-magnitude improvement in axion search sensitivity in exploiting a higher-order resonant mode. We find that their study is based on unrealistic cavity modeling and inappropriate choice of the figure of merit (FOM), which could mislead to the significant improvement in sensitivity. Considering a practical cavity structure and an appropriate FOM, we recalculate the significance of the scheme, which turns out to be not substantial.

physics.ins-det↗

arXiv2018

Freeze-In Dark Matter from a sub-Higgs Mass Clockwork Sector via the Higgs Portal

The clockwork mechanism allows extremely weak interactions and small mass scales to be understood in terms of the structure of a theory. A natural application of the clockwork mechanism is to the freeze-in mechanism for dark matter production. Here we consider a Higgs portal freeze-in dark matter model based on a scalar clockwork sector with a mass scale which is less than the Higgs boson mass. The dark matter scalar is the lightest scalar of the clockwork sector. Freeze-in dark matter is produced by the decay of thermal Higgs bosons to the clockwork dark matter scalars. We show that the mass of the dark matter scalar is typically in the 1-10 keV range and may be warm enough to have an observable effect on perturbation growth and Lyman-$α$ observations. Clockwork Higgs portal freeze-in models have a potentially observable collider phenomenology, with the Higgs boson decaying to missing energy in the form of pairs of long-lived clockwork sector scalars, plus a distribution of different numbers of quark and lepton particle-antiparticle pairs. The branching ratio to different numbers of quark and lepton pairs is determined by the clockwork sector parameters (the number of clockwork scalars $N$ and the clockwork charge $q$), which could therefore be determined experimentally if such Higgs decay modes are observed. In the case of a minimal Standard Model observable sector, the combination of nucleosynthesis and Lyman-$α$ constraints is likely to exclude on-shell Higgs decays to clockwork scalars, although off-shell Higgs decays would still be possible. On-shell Higgs decays to clockwork scalars can be consistent with cosmological constraints in simple extensions of the Standard Model with light singlet scalars.

hep-ph↗

arXiv2018

Emergence of Weyl metals driven by doped magnetic impurities in spin-orbit coupled semiconductors

Constructing an effective field theory in terms of doped magnetic impurities (described by an O(3) vector model with a random mass term), itinerant electrons of spin-orbit coupled semiconductors (given by a Dirac theory with a relatively large mass term), and effective interactions between doped magnetic ions and itinerant electrons (assumed by an effective Zeeman coupling term), we perform the perturbative renormalization group analysis in the one-loop level based on the dimensional regularization technique. As a result, we find that the mass renormalization in dynamics of itinerant electrons acquires negative feedback effects due to quantum fluctuations involved with the Zeeman coupling term, in contrast with that of the conventional problem of quantum electrodynamics, where such interaction effects enhance the fermion mass more rapidly. Recalling that the applied magnetic field decreases the band gap in the presence of spin-orbit coupling, this renormalization group analysis shows that the external magnetic field overcomes the renormalized band gap, allowed by doped magnetic impurities even without ferromagnetic ordering. In other words, the Weyl metal physics can be controlled by doping magnetic impurities into spin-orbit coupled semiconductors, even if the external magnetic field alone cannot realize the Weyl metal phase due to relatively large band gaps of semiconductors. Furthermore, we emphasize that quasiparticles do not exist in this emergent disordered Weyl metal phase due to correlations with strong magnetic fluctuations. This non-Fermi liquid type Weyl metal state may be regarded to be a novel metallic phase in the respect that a topologically nontrivial band structure appears in the vicinity of quantum criticality.

cond-mat.str-el↗

arXiv2018

Some network conditions for positive recurrence of stochastically modeled reaction networks

We consider discrete-space continuous-time Markov models of reaction networks and provide sufficient conditions for the following stability condition to hold: each state in a closed, irreducible component of the state space is positive recurrent; moreover the time required for a trajectory to enter such a component has finite expectation. The provided analytical results depend solely on the underlying structure of the reaction network and not on the specific choice of model parameters. Our main results apply to binary systems and our main analytical tool is the "tier structure" previously utilized successfully in the study of deterministic models of reaction networks.

math.PR↗

arXiv2018

Clockwork Higgs portal model for freeze-in dark matter

The clockwork mechanism can explain interactions which are dimensionally very weak without the need for very large mass scales. We present a model in which the clockwork mechanism generates the very small Higgs portal coupling and dark matter particle mass necessary to explain cold dark matter via the freeze-in mechanism. We introduce a TeV-scale scalar clockwork sector which couples to the Standard Model via the Higgs portal. The dark matter particle is the lightest scalar of the clockwork sector. We show that the freeze-in mechanism is dominated by decay of the heavy clockwork scalars to light dark matter scalars and Higgs bosons. In the model considered, we find that freeze-in dark matter is consistent with the clockwork mechanism for global charge $q$ in the range $2 \lesssim q \lesssim 4$ when the number of massive scalars is in the range $10 \leq N \leq 20$. The dark matter scalar mass and portal coupling are independent of $q$ and $N$. For a typical TeV-scale clockwork sector, the dark matter scalar mass is predicted to be of the order of a MeV.

hep-ph↗

arXiv2018

Chaotic initial conditions for nonminimally coupled inflation via a conformal factor with a zero

Nonminimally coupled inflation models based on a nonminimal coupling $ξϕ^{2} R$ and a $ϕ^{4}$ potential are in excellent agreement with the scalar spectral index observed by Planck. Here we consider the modification of these models by a conformal factor with a zero. This enables a nonminimally coupled model to have a Planck-scale potential energy density at large values of the inflaton field, which can account for the smooth, potential-dominated volume that is necessary for inflation to start. We show that models with a conformal factor zero generally predict a correlated increase of the spectral index $n_{s}$ and tensor-to-scalar ratio $r$. For values of $n_{s}$ that are within the present $2-σ$ bounds from Planck, modification by $Δr$ as large as 0.0013 is possible, which is large enough to be measured by next generation cosmic microwave background polarization satellites.

astro-ph.CO↗

arXiv2018

Inflaton condensate fragmentation: Analytical conditions and application to $α$-attractor models

We study the stability of an inflaton condensate in the presence of attractive inflaton self-interactions, in order to determine analytical conditions on the self-interaction couplings under which the condensate undergoes fragmentation. As an application of our results, we consider the stability of the inflaton condensate in $α$-attractor inflation. We show that the stability of the condensate depends upon the value of $α$. For the T-model with $n = 1$, we find that it is unstable for $α\lesssim 10^{-4}$. In this case it is expected that inflation will be followed by an oscillon-dominated era.

astro-ph.CO↗

arXiv2017

Restoration of Topological Surface State by Vacuum Annealing in Magnetically Doped Topological Insulator

The introduction of magnetic order on the surface of topological insulators in general breaks the two-dimensional character of topological surface state (TSS). Once the TSS disappears, it is improbable to restore the topological surface properties. In this report, we demonstrate that it is possible to restore the inherent TSS by ultra-high vacuum annealing. Starting from an antiferromagnetic Gd-doped Bi2Te3, that has surface state gap without TSS properties, after annealing we observed the gap closing as well as typical TSS features in physical properties. The microscopic mechanism of atomic migration and TSS restoration by annealing process is unraveled by the combination of scanning tunneling microscopy measurements and density functional theory calculations. This approach to control the surface of topological insulators and stabilize the TSS simply by vacuum annealing provides a new platform towards the exploitation of their topological properties.

cond-mat.mtrl-sci↗

arXiv2017

Gauss-Bonnet Chern-Simons gravitational wave leptogenesis

The gravitational Chern-Simons term coupled to an evolving axion is known to generate lepton number through the gravitational anomaly. We examine this leptogenesis scenario in the presence of the Gauss-Bonnet term over and above the gravitational Chern-Simons term. We find that the lepton production can be exponentially enhanced. The Gauss-Bonnet term creates CP-violating instability of gravitational waves that may appear transiently after inflation, and during the period of instability elliptically polarized gravitational waves are exponentially amplified at sub-horizon scales. This instability does not affect the spectrum of the cosmic microwave background as it occurs at much shorter length scales. In a typical scenario based on natural inflation, the observed baryon asymmetry of the Universe corresponds to the UV cutoff scale at $10^{14-16}$ GeV.

hep-th↗

arXiv2017

Higgs-portal assisted Higgs inflation with a sizeable tensor-to-scalar ratio

We show that the Higgs portal interactions involving extra dark Higgs field can save generically the original Higgs inflation of the standard model (SM) from the problem of a deep non-SM vacuum in the SM Higgs potential. Specifically, we show that such interactions disconnect the top quark pole mass from inflationary observables and allow multi-dimensional parameter space to save the Higgs inflation, thanks to the additional parameters (the dark Higgs boson mass $m_ϕ$, the mixing angle $α$ between the SM Higgs $H$ and dark Higgs $Φ$, and the mixed quartic coupling) affecting RG-running of the Higgs quartic coupling. The effect of Higgs portal interactions may lead to a larger tensor-to-scalar ratio, $0.08 \lesssim r \lesssim 0.1$, by adjusting relevant parameters in wide ranges of $α$ and $m_ϕ$, some region of which can be probed at future colliders. Performing a numerical analysis we find an allowed region of parameters, matching the latest Planck data.

hep-ph↗

arXiv2016

Leptonic Precision Test of Leptophilic Two-Higgs-Doublet Model

The type X (lepton-specific) two-Higgs-doublet model at large $\tanβ$ becomes leptophilic and thus allows a light pseudoscalar $A$ accommodating the observed muon $g-2$ deviation without conflicting with various hadronic constraints. On the other hand, it is strongly constrained by leptonic precision observables such as lepton universality test in the neutral and charged currents. Treating all the lepton universality data in a consistent way, we show how the current data constrain the parameter space of $m_A$ and $\tanβ$ for given degenerate masses of heavy Higgs bosons $H$ and $H^\pm$. While no overlapping region is found at $1σ$, a sizable region is still viable at $2σ$ for $H/H^\pm$ masses at around 200$\sim$400 GeV.

hep-ph↗

arXiv2015

Testing supersymmetric Higgs inflation with non-Gaussianity

We investigate multi-field signatures of the nonminimally coupled supersymmetric Higgs inflation-type cosmological scenario, focusing on the two-field Higgs-lepton inflation model as a concrete example. This type of inflationary model is realized in a theory beyond the Standard Model embedded in supergravity with a noncanonical Kähler potential. We employ the backward $δN$ formalism to compute cosmological observables, including the scalar and tensor power spectra, the spectral indices, the tensor-to-scalar ratio and the local-type nonlinearity parameter. The trajectory of the inflaton is controlled by the initial conditions of the inflaton as well as by the coefficients in the Kähler potential. We analyze the bispectrum of the primordial fluctuations when the inflaton trajectory deviates from a straight line, and obtain constraints on the noncanonical terms of the Kähler potential using the Planck satellite data. Our analysis represents a concrete particle phenomenology-based case study of inflation in which primordial non-Gaussianities can reveal aspects of supergravity.

hep-ph↗