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Catumba, G.*; Hiraguchi, Atsuki; Hou, G. W.-S.*; Jansen, K.*; Kao, Y.-J.*; David Lin, C.-J.*; Ramos, A.*; Sarkar, M.*
Proceedings of Science (Internet), 466, p.145_1 - 145_10, 2025/12
The custodial Two-Higgs-Doublet-Model with SU(2) gauge fields is studied on the lattice. This model has the same global symmetry structure as the Standard Model but the additional Higgs field enlarges the scalar spectrum and opens the possibility for the occurrence of spontaneous symmetry breaking of the global symmetries. Both the spectrum and the running of the gauge coupling of the custodial 2HDM are studied on a line of constant Standard Model physics with cutoff ranging from 300 to 600 GeV. The lower bounds of the realizable masses for the additional BSM scalar states are found to be well bellow the W boson mass. In fact, for the choice of quartic couplings in this work the estimated lower mass for one of the BSM states is found to be about 
0.2 
and independent of the cutoff.
Catumba, G.*; Hiraguchi, Atsuki; Hou, W.-S.*; Jansen, K.*; Kao, Y.-J.*; David Lin, C.-J.*; Ramos, A.*; Sarkar, M.*
Journal of High Energy Physics (Internet), 2025(10), p.214_1 - 214_34, 2025/10
Times Cited Count：0 Percentile：0.00(Physics, Particles & Fields)The SU(2)-gauged custodial two-Higgs-doublet model, which shares the same global-symmetry properties with the standard model, is studied non-perturbatively on the lattice. The additional Higgs doublet enlarges the scalar spectrum and opens the possibility for spontaneous breaking of the global symmetry. In this work we start by showing the occurrence of spontaneous breaking of the custodial symmetry in a region of the parameter space of the model. Following this, both the spectrum and the running of the gauge coupling are examined at weak quartic couplings in the presence of the custodial symmetry. The calculations are performed with energy cutoffs ranging from 300 to 600 GeV on a line of constant standard model physics, obtained by tuning bare couplings to fix the ratio between the masses of the Higgs and the W bosons, as well as the value of the renormalized gauge coupling at the scale of the W boson mass. The realizable masses for the additional scalar states are explored. For the choice of bare quartic couplings in this work, the estimated lower bound of these masses is found to be well below the W boson mass, and independent of the cutoff. We also study the finite temperature electroweak transition along this line of constant standard model physics, revealing properties of a smooth crossover behavior.
Catumba, G.*; Hiraguchi, Atsuki; Hou, W.-S.*; Jansen, K.*; Kao, Y.-J.*; David Lin, C.-J.*; Ramos, A.*; Sarkar, M.*
Physical Review Research (Internet), 6(4), p.043172_1 - 043172_12, 2024/11
Gauge theories with matter fields in various representations play an important role in different branches of physics. Recently, it was proposed that several aspects of the interesting pseudogap phase of cuprate superconductors near optimal doping may be explained by an emergent SU(2) gauge symmetry. Around the transition with positive hole-doping, one can construct a (2+1)-dimensional SU(2) gauge theory coupled to four adjoint scalar fields which gives rise to a rich phase diagram with a myriad of phases having different broken symmetries. We study the phase diagram of this model on the Euclidean lattice using the Hybrid Monte Carlo algorithm. We find the existence of multiple broken phases as predicted by previous mean field studies. Depending on the quartic couplings, the SU(2) gauge symmetry is broken down either to U(1) or 
in the perturbative description of the model. We further study the confinement-deconfinement transition in this theory, and find that both the broken phases are deconfining in the range of volumes that we studied. However, there exists a marked difference in the behavior of the Polyakov loop between the two phases.
Catumba, G.*; Hiraguchi, Atsuki; W.-S. Hou, G.*; Jansen, K.*; Kao, Y.-J.*; David Lin, C.-J.*; Ramos, A.*; Sarkar, M.*
Proceedings of Science (Internet), 453, p.362_1 - 362_7, 2024/11
We study a 3-dimensional SU(2) gauge theory with 4 Higgs fields which transform under the adjoint representation of the gauge group, that has been recently proposed by Sachdev et al. to explain the physics of cuprate superconductors near optimal doping. The symmetric confining phase of the theory corresponds to the usual Fermi-liquid phase while the broken (Higgs) phase is associated with the interesting pseudogap phase of cuprates. We employ the Hybrid Monte-Carlo algorithm to study the phase diagram of the theory. We find the existence of a variety of broken phases in qualitative accordance with earlier mean-field predictions and discuss their role in cuprates. In addition, we investigate the behavior of Polyakov loop to probe the confinement/deconfinement phase transition, and find that the Higgs phase hosts a stable deconfining phase consistent with previous studies.
gauge fieldsCatumba, G.*; Hiraguchi, Atsuki; W.-S. Hou, G.*; Jansen, K.*; Kao, Y.-J.*; David Lin, C.-J.*; Ramos, A.*; Sarkar, M.*
Proceedings of Science (Internet), 453, p.87_1 - 87_9, 2024/11
We study the most general Two Higgs Doublet Model with gauge fields on the lattice. The phase space is probed through the computation of gauge-invariant global observables serving as proxies for order parameters. In each phase, the spectrum of the theory is analysed for different combinations of bare couplings and different symmetry breaking patterns. The scale setting and determination of the running gauge coupling are performed through the Wilson flow computation of the action density.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K.*; Bourg, I.*; Okumura, Masahiko
no journal, ,
In the geological disposal of high-level radioactive waste, bentonite plays an important role in retarding radionuclide migration by adsorbing cationic species. Cesium ions (Cs
), in particular, are strongly adsorbed by montmorillonite, the main component of bentonite. However, the detailed adsorption states and mechanisms remain unclear. We employed classical molecular dynamics simulations to investigate the adsorption behavior of Cs and sodium ions (Na) from bulk water into the interlayer of Na-montmorillonite, by evaluating their free energy profiles. Moreover, we evaluated the dependence of the layer charge on the free energy profiles. As a result, our simulations reproduced the experimental trend showing that Cs is more strongly adsorbed on Na-montmorillonite than Na, as the layer charge increases. In the presentation, we will also discuss the detailed adsorption mechanisms, and comparisons with experimental data.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K.*; Bourg, I.*; Okumura, Masahiko
no journal, ,
In the geological disposal of high-level radioactive waste, bentonite plays a crucial role in retarding radionuclide migration by adsorbing cationic species. Cesium ions (Cs), in particular, are strongly adsorbed by montmorillonite, the main component of bentonite. However, the detailed adsorption states and mechanisms remain unclear. We employed classical molecular dynamics simulations to investigate the adsorption behavior of Cs and sodium ions (Na) from bulk water into the interlayer of Na-montmorillonite, by evaluating free energy profiles. Our results revealed that Cs adsorbs more strongly into the interlayer than Na due to the formation of the inner- and outer-sphere complexes of Cs and Na, respectively. In the presentation, we will also discuss the fundamentals of classical molecular dynamics, the physical origin of the free energy profiles, detailed adsorption mechanisms, and comparisons with experimental data.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
In geological disposal of high-level radioactive nuclides, bentonite, a buffer, adsorbs cations and delays nuclide migration. Cesium ions are strongly adsorbed onto montmorillonite, which is the main component of Bentonite. Since the buffer material can reach elevated temperatures, understanding the temperature dependence of cesium adsorption and diffusion is essential to ensure the long-term safety of geological disposal. In this study, we performed classical molecular dynamics simulations of a system containing Na-montmorillonite with edges, water molecules, and a cesium ion at temperatures ranging from 300 K to 370 K. The simulation results indicate that the adsorption strength is independent of temperature within this range. In this talk, we discuss the temperature dependence of the cesium diffusion constant and compare it with experimental results.
Hiraguchi, Atsuki
no journal, ,
Quark confinement is still an unsolved problem, and it has been studied in lattice gauge theories. One of the ideas of its mechanism is the dual Meissner effect. In this idea, condensation of color magnetic monopoles leads to confinement, and it is confirmed that monopoles contribute to confinement in lattice gauge Monte-Carlo simulations. Recently, topological data analysis has been employed to analyze monopole loops and distinguish phase boundaries of confinement in compact U(1) gauge theory and gauge fixed SU(3) gauge theory. In this research, we apply the persistent homology, which is a topological data analysis, to analyze space distributions of monopole loops and configurations of Higgs fields in SU(2)Higgs models. In addition, we discuss the connection between analysis results and physical quantities.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
The migration behavior of radionuclides in clay minerals used as buffer material must be clarified for the long-term safety of geological disposal of high-level radioactive waste. We can investigate diffusion/adsorption behavior of cesium ion and sodium ion in clay minerals and water systems at molecular scale using molecular dynamics simulation on a supercomputing system. In this study, we evaluate the free energy profiles of the cesium and sodium ions adsorption to the montmorillonite interlayer from bulk water in mesopore. We found that the free energies in the interlayer of Na-montmorillonite are smaller than those in the bulk water for the cesium and sodium ions, and the averaged free energy value for cesium in the interlayer is lower than that for sodium. This result shows that cesium ion is more strongly adsorbed to the interlayer of Na-montmorillonite than sodium ion. Moreover, we found differences in the shape of these free energy profiles in the interlayer. The free energy profile for the cesium ion has a spiky structure with many local minimums, although that for the sodium ion is almost uniform. These results suggest that the cesium ion forms the inner-sphere complex at these local minimums and the sodium ion forms the outer-sphere complex. Furthermore, we investigated salinity dependence on the free energy profiles. We confirmed that the affinities of both cations to Na-montmorillonite decrease with increasing salinity, and the adsorption mechanism of these cations does not depend on salinity. In the presentation, we discuss the free energy profiles with different layer charges, interlayer distances, etc.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
Bentonite is the primary buffer material to inhibit radionuclide diffusion in geological disposal of high-level radioactive waste. Cesium ions are strongly adsorbed by montmorillonite, the main component of bentonite. However, the detailed adsorption states and mechanisms remain unclear. We conducted classical molecular dynamics simulations of the cesium adsorption on a Na-montmorillonite at 300 K, 330K, 350 K, and 370 K to investigate the temperature dependence of cesium adsorption by evaluating free energy profiles. Our simulation showed that cesium ions consistently adsorb within the interlayer and form inner-sphere complexes at all temperatures. This temperature-independent behavior supports bentonite's reliability as a buffer material for high-level radioactive waste even at high temperatures.
Hiraguchi, Atsuki; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Okumura, Masahiko
no journal, ,
In order to evaluate the long-term safety of geological disposal of high-level radioactive waste, it is necessary to elucidate and model the migration behavior of radionuclides. Clay minerals are used as buffer materials to inhibit radionuclide migration, but the details of their diffusion behavior on a molecular scale are unknown. In this study, we perform large-scale molecular dynamics simulations of cesium diffusion in a clay mineral-water system to clarify the diffusion behavior of cesium on a molecular scale.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
In order to evaluate the long-term safety of geological disposal of high-level radioactive waste, it is necessary to clarify and model the migration behavior of radionuclides in clay minerals used as buffer material on a molecular scale. In this study, we perform classical molecular dynamics simulations in clay minerals-water systems and evaluate free-energy profiles of clay minerals to clarify and model the diffusion behavior of cesium on a molecular scale.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
Understanding the radionuclide diffusion phenomena is crucial for the safe geological disposal of high-level radioactive waste. The diffusion in clay-water systems is particularly important for the performance of the artificial barrier made of bentonite. Numerical simulation is one of the best research methods for understanding the phenomenon at the microscopic level. Recently, large-scale molecular dynamics (MD) simulations of the systems with clay particles and water molecules were realized. In this presentation, we will show numerical simulation results of diffusion of cesium in the large system with MD. Our recent results suggest that cesium is less diffuse than sodium.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
The migration behavior of radionuclides in clay minerals used as buffer material must be clarified for the long-term safety of geological disposal of high-level radioactive waste. The recent development of supercomputers enables us to perform large-scale classical molecular dynamics (MD) simulations to evaluate the adsorption properties of cation to clay minerals. We evaluated the free-energy profiles of cesium adsorption from mesopore to the interlayer of Na-montmorillonite by classical MD on a supercomputer. We found that the free-energy profiles of cesium adsorption depend on the interlayer distance of the Na-montmorillonite and mesopore salinity in the water system. In the presentation, we also discuss the distribution and diffusion coefficients of cesium ions.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
In order to evaluate the long-term safety of geological disposal of high-level radioactive waste, it is necessary to understand the migration behavior of radionuclides in clay minerals used as buffer materials. In this study, the difference in the diffusion behavior of cesium and sodium ions in Na-montmorillonite is analyzed by evaluating the free energy using classical molecular dynamics simulations.
Hiraguchi, Atsuki; Zheng, X.*; Underwood, T. R.*; Kobayashi, Keita; Yamaguchi, Akiko; Itakura, Mitsuhiro; Machida, Masahiko; Rosso, K. M.*; Bourg, I. C.*; Okumura, Masahiko
no journal, ,
The migration behavior of radionuclides in clay minerals used as buffer material must be clarified for the long-term safety of geological disposal of high-level radioactive waste. We can investigate diffusion/adsorption behavior of cesium ion and sodium ion in clay minerals and water systems at molecular scale using molecular dynamics simulation on a supercomputing system. In this study, we evaluated the free energy profiles of cesium and sodium ions adsorption to the interlayer of Na-montmorillonite from bulk water in mesopore. As a result, we found that the minimum of free energy profiles of these cations locates in the interlayer of Na-montmorillonite, and the minimum of free energy profile of cesium is lower than that of sodium. This result shows that the affinity of cesium ion to Na-montmorillonite is stronger than that of sodium ion. Moreover, we confirmed that the affinities of both cations to Na-montmorillonite decrease with salinity increase, and these cations maintain their adsorption mechanism. In the presentation, we discuss layer charge and layer size dependence on the free energy profiles of these cations.
