Search

The observed Higgs mass MH=125.9±0.4GeV leads to the criticality of the standard model, that is, the Higgs potential becomes flat around the scale 10[17-18]GeV for the top mass 171.3 GeV. Earlier we proposed a Higgs inflation scenario in which this criticality plays a crucial role. In this paper, we investigate the detailed cosmological predictions of this scenario in light of the latest Planck and BICEP2 results. We also consider the Higgs portal scalar dark matter model, and compute the Higgs one-loop effective potential with the two-loop renormalization group improvement. We find a constraint on the coupling between the Higgs boson and dark matter which depends on the inflationary parameters.

We systematically search intersecting D-brane models, which just realize the Standard Model chiral matter contents and gauge symmetry. We construct new classes of non-supersymmetric Standard Model-like models. We also study the gauge coupling constants of these models. The tree level gauge coupling is a function of the compactification moduli, the string scale, the string coupling and the winding numbers of D-branes. By tuning them, we examine whether the models can explain the experimental values of gauge couplings. As a result, we find that the string scale should be greater than 10[14-15] GeV if the compactification scale and the string scale are of the same order.

We consider the Standard Model with a new scalar field X which is an n[X] representation of the SU(2)[L] with a hypercharge Y[X]. The renormalization group running effects on the new scalar quartic coupling constants are evaluated. Even if we set the scalar quartic coupling constants to be zero at the scale of the new scalar field, the coupling constants are induced by the one-loop effect of the weak gauge bosons. Once non-vanishing couplings are generated, the couplings rapidly increase by renormalization group effect of the quartic coupling constant itself. As a result, the Landau pole appears below Planck scale if n[X]≥4. We find that the scale of the obtained Landau pole is much lower than that evaluated by solving the one-loop beta function of the gauge coupling constants.

We investigate the Higgs potential beyond the Planck scale in the superstring theory, under the assumption that the supersymmetry is broken at the string scale. We identify the Higgs field as a massless state of the string, which is indicated by the fact that the bare Higgs mass can be zero around the string scale. We find that, in the large field region, the Higgs potential is connected to a runaway vacuum with vanishing energy, which corresponds to opening up an extra dimension. We verify that such universal behavior indeed follows from the toroidal compactification of the nonsupersymmetric SO(16)×SO(16) heterotic string theory. We show that this behavior fits in the picture that the Higgs field is the source of the eternal inflation. The observed small value of the cosmological constant of our universe may be understood as the degeneracy with this runaway vacuum, which has vanishing energy, as is suggested by the multiple point criticality principle.

The measured values of the Higgs and top masses and of the strong gauge coupling constant point to the near-criticality of the Standard Model, where two vacua at the electroweak and Planck scales are quasidegenerate. We argue that the criticality is required by the occurrence of an eternal topological inflation induced by the Higgs potential. The role of this inflation is to continuously create a sufficiently flat and homogeneous Universe, providing the necessary initial condition for the subsequent slow-roll inflation that generates the density perturbations of the right magnitude. While the condition for the topological Higgs inflation is only marginally satisfied in the Standard Model, it can be readily satisfied if one introduces the right-handed neutrinos and/or the nonminimal coupling to gravity; currently unknown quantum gravity corrections to the potential may also help. We also discuss the B−L Higgs inflation as a possible origin of the observed density perturbations. Its necessary initial condition, the restored B−L symmetry, can be naturally realized by the preceding topological Higgs inflation.

We revisit the discrete dark matter model with the A(4) flavor symmetry originally introduced by M.Hirsch et. al. We show that radiative corrections can lead to non-zero theta(13) and the non-zero mass for the lightest neutrino. We find an interesting relation among neutrino mixing parameters and it indicates the sizable deviation of s(23) from the maximal angle s(23)(2) = 1/2 and the degenerate mass spectrum for neutrinos. Also we study the possibilities that the right-handed neutrino is a dark matter candidate. Assuming that the thermal freeze-out explains observed dark matter abundance, TeV-scale right-handed neutrino and flavored scalar bosons are required. In such a case, the flavor symmetry plays an important role for the suppression of lepton flavor violating processes as well as for the stability of dark matter. We show that this scenario is viable within currently existing constraints from collider, low energy experiments and cosmological observations.

Yuta Hamada, Hikaru Kawai, and Kin-ya Oda. Bare Higgs mass at Planck scale. Phys. Rev. D 87, 053009, 2013. https://doi.org/10.1103/PhysRevD.87.053009., Yuta Hamada, Hikaru Kawai, and Kin-ya Oda. Erratum: Bare Higgs mass at Planck scale [Phys. Rev. D 87, 053009 (2013)]. Phys. Rev. D 89, 059901, 2014. https://doi.org/10.1103/PhysRevD.89.059901., We compute one- and two-loop quadratic divergent contributions to the bare Higgs mass in terms of the bare couplings in the Standard Model. We approximate the bare couplings, defined at the ultraviolet cutoff scale, by the MS-bar ones at the same scale, which are evaluated by the two-loop renormalization group equations for the Higgs mass around 126GeV in the Standard Model. We obtain the cutoff scale dependence of the bare Higgs mass, and examine where it becomes zero. We find that when we take the current central value for the top quark pole mass, 173GeV, the bare Higgs mass vanishes if the cutoff is about 10^{23}GeV. With a 1.3 sigma smaller mass, 170GeV, the scale can be of the order of the Planck scale.

Yuta Hamada, Hikaru Kawai, Yukari Nakanishi, Kin-ya Oda. Cosmological implications of Standard Model criticality and Higgs inflation. Nuclear Physics B, Vol. 953, 2020, 114946. https://doi.org/10.1016/j.nuclphysb.2020.114946.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda, and Seong Chan Park. Higgs Inflation is Still Alive after the Results from BICEP2. Phys. Rev. Lett. 112, 241301, 2014. https://doi.org/10.1103/PhysRevLett.112.241301.

Hamada, Y., Kawai, H. & Oda, Ky. Predictions on mass of Higgs portal scalar dark matter from Higgs inflation and flat potential. J. High Energ. Phys. 2014, 26 (2014). https://doi.org/10.1007/JHEP07(2014)026.

Yuta Hamada, Hikaru Kawai, Kiyoharu Kawana, Kin-ya Oda, Kei Yagyu. Minimal scenario of Criticality for Electroweak scale, Neutrino Masses, Dark Matter, and Inflation. https://arxiv.org/abs/2102.04617.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda, and Seong Chan Park. Higgs Inflation is Still Alive after the Results from BICEP2. Phys. Rev. Lett. 112, 241301, 2014. https://doi.org/10.1103/PhysRevLett.112.241301.

Hamada, Y., Kawai, H. & Oda, Ky. Predictions on mass of Higgs portal scalar dark matter from Higgs inflation and flat potential. J. High Energ. Phys. 2014, 26 (2014). https://doi.org/10.1007/JHEP07(2014)026.

Yuta Hamada, Hikaru Kawai, Yukari Nakanishi, Kin-ya Oda. Cosmological implications of Standard Model criticality and Higgs inflation. Nuclear Physics B, Vol. 953, 2020, 114946. https://doi.org/10.1016/j.nuclphysb.2020.114946.

Yuta Hamada, Hikaru Kawai, and Kin-ya Oda. Eternal Higgs inflation and the cosmological constant problem. Phys. Rev. D 92, 045009, 2015. https://doi.org/10.1103/PhysRevD.92.045009., We investigate the Higgs potential beyond the Planck scale in the superstring theory, under the assumption that the supersymmetry is broken at the string scale. We identify the Higgs field as a massless state of the string, which is indicated by the fact that the bare Higgs mass can be zero around the string scale. We find that, in the large field region, the Higgs potential is connected to a runaway vacuum with vanishing energy, which corresponds to opening up an extra dimension. We verify that such universal behavior indeed follows from the toroidal compactification of the nonsupersymmetric SO(16)×SO(16) heterotic string theory. We show that this behavior fits in the picture that the Higgs field is the source of the eternal inflation. The observed small value of the cosmological constant of our universe may be understood as the degeneracy with this runaway vacuum, which has vanishing energy, as is suggested by the multiple point criticality principle.

Yuta Hamada, Hikaru Kawai, Yukari Nakanishi, and Kin-ya Oda. Meaning of the field dependence of the renormalization scale in Higgs inflation. Phys. Rev. D 95, 103524, 2017. https://doi.org/10.1103/PhysRevD.95.103524., We consider the prescription dependence of the Higgs effective potential under the presence of general nonminimal couplings. We evaluate the fermion loop correction to the effective action in a simplified Higgs-Yukawa model whose path integral measure takes simple form either in the Jordan or Einstein frame. The resultant effective action becomes identical in both cases when we properly take into account the quartically divergent term coming from the change of measure. Working in the counterterm formalism, we clarify that the difference between the prescriptions I and II comes from the counter term to cancel the logarithmic divergence. This difference can be absorbed into the choice of tree-level potential from the infinitely many possibilities, including all the higher-dimensional terms. We also present another mechanism to obtain a flat potential by freezing the running of the effective quartic coupling for large field values, using the nonminimal coupling in the gauge kinetic function.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda. Minimal Higgs inflation. Progress of Theoretical and Experimental Physics, Volume 2014, Issue 2, February 2014, 023B02. https://doi.org/10.1093/ptep/ptt116., We consider a possibility that the Higgs field in the Standard Model (SM) serves as an inflaton when its value is around the Planck scale. We assume that the SM is valid up to an ultraviolet cutoff scale \Lambda, which is slightly below the Planck scale, and that the Higgs potential becomes almost flat above \Lambda. Contrary to the ordinary Higgs inflation scenario, we do not assume the huge non-minimal coupling, of O(10^4), of the Higgs field to the Ricci scalar. We find that \Lambda must be less than 5*10^{17}GeV in order to explain the observed fluctuation of the cosmic microwave background, no matter how we extrapolate the Higgs potential above \Lambda. The scale 10^{17}GeV coincides with the perturbative string scale, which suggests that the SM is directly connected with the string theory. For this to be true, the top quark mass is restricted to around 171GeV, with which \Lambda can exceed 10^{17}GeV. As a concrete example of the potential above \Lambda, we propose a simple log type potential. The predictions of this specific model for the e-foldings N_*=50--60 are consistent with the current observation, namely, the scalar spectral index is n_s=0.977--0.983 and the tensor to scalar ratio 0

Yuta Hamada, Hikaru Kawai, and Kin-ya Oda. Bare Higgs mass at Planck scale. Phys. Rev. D 87, 053009, 2013. https://doi.org/10.1103/PhysRevD.87.053009., Yuta Hamada, Hikaru Kawai, and Kin-ya Oda. Erratum: Bare Higgs mass at Planck scale [Phys. Rev. D 87, 053009 (2013)]. Phys. Rev. D 89, 059901, 2014. https://doi.org/10.1103/PhysRevD.89.059901., We compute one- and two-loop quadratic divergent contributions to the bare Higgs mass in terms of the bare couplings in the Standard Model. We approximate the bare couplings, defined at the ultraviolet cutoff scale, by the MS-bar ones at the same scale, which are evaluated by the two-loop renormalization group equations for the Higgs mass around 126GeV in the Standard Model. We obtain the cutoff scale dependence of the bare Higgs mass, and examine where it becomes zero. We find that when we take the current central value for the top quark pole mass, 173GeV, the bare Higgs mass vanishes if the cutoff is about 10^{23}GeV. With a 1.3 sigma smaller mass, 170GeV, the scale can be of the order of the Planck scale.

Hamada, Y., Kawai, H., Oda, Ky. et al. Dark matter in minimal dimensional transmutation with multicritical-point principle. J. High Energ. Phys. 2021, 87 (2021). https://doi.org/10.1007/JHEP01(2021)087., We investigate a model with two real scalar fields that minimally generates exponentially different scales in an analog of the Coleman-Weinberg mechanism. The classical scale invariance — the absence of dimensionful parameters in the tree-level action, required in such a scale generation — can naturally be understood as a special case of the multicritical-point principle. This two-scalar model can couple to the Standard Model Higgs field to realize a maximum multicriticality (with all the dimensionful parameters being tuned to critical values) for field values around the electroweak scale, providing a generalization of the classical scale invariance to a wider class of criticality. As a bonus, one of the two scalars can be identified as Higgs-portal dark matter. We find that this model can be consistent with the constraints from dark matter relic abundance, its direct detection experiments, and the latest LHC data, while keeping the perturbativity up to the reduced Planck scale. We then present successful benchmark points satisfying all these constraints: the mass of dark matter is a few TeV, and its scattering cross section with nuclei is of the order of 10−9 pb, reachable in near future experiments. The mass of extra Higgs boson H is smaller than or of the order of 100 GeV, and the cross section of e+e− → ZH can be of fb level for collision energy 250 GeV, targetted at future lepton colliders.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda, and Seong Chan Park. Higgs inflation from standard model criticality. Phys. Rev. D 91, 053008, 2015. https://doi.org/10.1103/PhysRevD.91.053008., The observed Higgs mass MH=125.9±0.4GeV leads to the criticality of the standard model, that is, the Higgs potential becomes flat around the scale 1017-18GeV for the top mass 171.3 GeV. Earlier we proposed a Higgs inflation scenario in which this criticality plays a crucial role. In this paper, we investigate the detailed cosmological predictions of this scenario in light of the latest Planck and BICEP2 results. We also consider the Higgs portal scalar dark matter model, and compute the Higgs one-loop effective potential with the two-loop renormalization group improvement. We find a constraint on the coupling between the Higgs boson and dark matter which depends on the inflationary parameters.

Yuta Hamada, Kin-ya Oda, and Fuminobu Takahashi. Topological Higgs inflation: Origin of Standard Model criticality. Phys. Rev. D 90, 097301, 2014. https://doi.org/10.1103/PhysRevD.90.097301., The measured values of the Higgs and top masses and of the strong gauge coupling constant point to the near-criticality of the Standard Model, where two vacua at the electroweak and Planck scales are quasidegenerate. We argue that the criticality is required by the occurrence of an eternal topological inflation induced by the Higgs potential. The role of this inflation is to continuously create a sufficiently flat and homogeneous Universe, providing the necessary initial condition for the subsequent slow-roll inflation that generates the density perturbations of the right magnitude. While the condition for the topological Higgs inflation is only marginally satisfied in the Standard Model, it can be readily satisfied if one introduces the right-handed neutrinos and/or the nonminimal coupling to gravity; currently unknown quantum gravity corrections to the potential may also help. We also discuss the B-L Higgs inflation as a possible origin of the observed density perturbations. Its necessary initial condition, the restored B-L symmetry, can be naturally realized by the preceding topological Higgs inflation.

Hamada, Y., Ibe, M., Muramatsu, Y. et al. Proton decay and axion dark matter in SO(10) grand unification via minimal left–right symmetry. Eur. Phys. J. C 80, 482 (2020). https://doi.org/10.1140/epjc/s10052-020-7922-x., We study the proton lifetime in the SO(10) Grand Unified Theory (GUT), which has the left–right (LR) symmetric gauge theory below the GUT scale. In particular, we focus on the minimal model without the bi-doublet Higgs field in the LR symmetric model, which predicts the LR-breaking scale at around 10 10 - 12 GeV. The Wilson coefficients of the proton decay operators turn out to be considerably larger than those in the minimal SU(5) GUT model especially when the Standard Model Yukawa interactions are generated by integrating out extra vector-like multiplets. As a result, we find that the proton lifetime can be within the reach of the Hyper-Kamiokande experiment even when the GUT gauge-boson mass is in the 10 16–10 17 GeV range. We also show that the mass of the extra vector-like multiplets can be generated by the Peccei–Quinn symmetry breaking in a consistent way with the axion dark matter scenario.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda. Bare Higgs mass and potential at ultraviolet cutoff. https://arxiv.org/abs/1305.7055., We first review the current status of the top mass determination paying attention to the difference between the MS-bar and pole masses. Then we present our recent result on the bare Higgs mass at a very high ultraviolet cutoff scale.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda. Minimal Higgs inflation. Progress of Theoretical and Experimental Physics, Volume 2014, Issue 2, February 2014, 023B02. https://doi.org/10.1093/ptep/ptt116., We consider a possibility that the Higgs field in the Standard Model (SM) serves as an inflaton when its value is around the Planck scale. We assume that the SM is valid up to an ultraviolet cutoff scale \Lambda, which is slightly below the Planck scale, and that the Higgs potential becomes almost flat above \Lambda. Contrary to the ordinary Higgs inflation scenario, we do not assume the huge non-minimal coupling, of O(10^4), of the Higgs field to the Ricci scalar. We find that \Lambda must be less than 5*10^{17}GeV in order to explain the observed fluctuation of the cosmic microwave background, no matter how we extrapolate the Higgs potential above \Lambda. The scale 10^{17}GeV coincides with the perturbative string scale, which suggests that the SM is directly connected with the string theory. For this to be true, the top quark mass is restricted to around 171GeV, with which \Lambda can exceed 10^{17}GeV. As a concrete example of the potential above \Lambda, we propose a simple log type potential. The predictions of this specific model for the e-foldings N_*=50--60 are consistent with the current observation, namely, the scalar spectral index is n_s=0.977--0.983 and the tensor to scalar ratio 0

Yuta Hamada, Hikaru Kawai, Yukari Nakanishi, and Kin-ya Oda. Meaning of the field dependence of the renormalization scale in Higgs inflation. Phys. Rev. D 95, 103524, 2017. https://doi.org/10.1103/PhysRevD.95.103524., We consider the prescription dependence of the Higgs effective potential under the presence of general nonminimal couplings. We evaluate the fermion loop correction to the effective action in a simplified Higgs-Yukawa model whose path integral measure takes simple form either in the Jordan or Einstein frame. The resultant effective action becomes identical in both cases when we properly take into account the quartically divergent term coming from the change of measure. Working in the counterterm formalism, we clarify that the difference between the prescriptions I and II comes from the counter term to cancel the logarithmic divergence. This difference can be absorbed into the choice of tree-level potential from the infinitely many possibilities, including all the higher-dimensional terms. We also present another mechanism to obtain a flat potential by freezing the running of the effective quartic coupling for large field values, using the nonminimal coupling in the gauge kinetic function.

Yuta Hamada, Hikaru Kawai, Kin-ya Oda, and Seong Chan Park. Higgs inflation from standard model criticality. Phys. Rev. D 91, 053008, 2015. https://doi.org/10.1103/PhysRevD.91.053008., The observed Higgs mass MH=125.9±0.4GeV leads to the criticality of the standard model, that is, the Higgs potential becomes flat around the scale 1017-18GeV for the top mass 171.3 GeV. Earlier we proposed a Higgs inflation scenario in which this criticality plays a crucial role. In this paper, we investigate the detailed cosmological predictions of this scenario in light of the latest Planck and BICEP2 results. We also consider the Higgs portal scalar dark matter model, and compute the Higgs one-loop effective potential with the two-loop renormalization group improvement. We find a constraint on the coupling between the Higgs boson and dark matter which depends on the inflationary parameters.