Yuta Hamada

Bare Higgs mass at Planck scale

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, dened at the ultraviolet cuto scale, by the MS ones at the same scale, which are evaluated by the two-loop renormalization group equations for the Higgs mass around 126 GeV in the Standard Model. We obtain the cuto scale dependence of the bare Higgs mass, and examine where it becomes zero. We nd that when we take the current central value for the top quark pole mass, 173 GeV, the bare Higgs mass vanishes if the cuto is about 10 23 GeV. With a 1.3 smaller mass, 170 GeV, the scale can be of the order of

Higgs inflation from standard model criticality

In this chapter, we investigate the possibility that the SM Higgs boson plays the role of an inflation in light of the discovery of the Higgs boson. In 2007, Bezurkov and Shaposhnikov first pointed out this possibility. The successful Higgs inflation is realized if the non-minimal coupling between the Higgs H and scalar curvature \(\mathcal {R}\), \(\xi |H|^2 \mathcal {R}\), is introduced. \(\xi \) is the coupling constant, and very large value, \(\xi \sim 10^5\), is required for successful inflation. However, the observation of the Higgs and determination of its mass changes the situation. As we have seen in Chap. 2, the Higgs self coupling and its beta function becomes zero at very high scale, which means that the Higgs potential is very flat around string/Planck scale. This opens up the new possibilities of the Higgs inflation, which we will present here. In Sect. 3.1, we present the general argument of the Higgs inflation above the SM cutoff \(\Lambda \). In Sect. 3.2, we show that non-minimal coupling \(\xi \) can be as small as \(\mathcal {O}(10)\).

Predictions on mass of Higgs portal scalar dark matter from Higgs inflation and flat potential

A bstractWe consider the Higgs portal Z2 scalar model as the minimal extension of the Standard Model (SM) to incorporate the dark matter. We analyze this model by using the two-loop renormalization group equations. We find that the dark matter mass is bounded to be lighter than 1000 GeV within the framework that we have proposed earlier, where the Higgs inflation occurs above the SM cutoff Λ, thanks to the fact that the Higgs potential becomes much smaller than its typical value in the SM: V ≪ Λ4. We can further fix the dark matter mass to be 400 GeV < mDM< 470 GeV if we impose that the cutoff is at the string scale Λ ~ 1017 GeV and that the Higgs potential becomes flat around Λ, as is required by the multiple point principle or by the Higgs inflation at the critical point. This prediction is testable by the dark matter detection experiments in the near future. In this framework, the dark matter and top quark masses are strongly correlated, which is also testable.

750 GeV diphoton resonance and inflation

We study the possibility of a heavy scalar or pseudoscalar in TeV-scale beyond the Standard Model scenarios being the inflaton of the early universe in light of the recent O(750) GeV diphoton excess at the LHC. We consider a scenario in which the new scalar or pseudoscalar couples to the Standard Model gauge bosons at the loop level through new massive Standard Model charged vectorlike fermions with or without dark fermions. We calculate the renormalization group running of both the Standard Model and the new scalar couplings, and present two different models that are perturbative and with a stabilized vacuum up to near the Planck scale. Thus, the Standard Model Higgs and this possible new resonance may still preserve the minimalist features of Higgs inflation.

Landau pole in the Standard Model with weakly interacting scalar fields

Abstract 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.

Minimal Higgs inflation

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

Evidence of the Big Fix

We give an evidence of the Big Fix. The theory of wormholes and multiverse suggests that the parameters of the Standard Model are fixed in such a way that the total entropy at the late stage of the universe is maximized, which we call the maximum entropy principle. In this paper, we discuss how it can be confirmed by the experimental data, and we show that it is indeed true for the Higgs vacuum expectation value vh. We assume that the baryon number is produced by the sphaleron process, and that the current quark masses, the gauge couplings and the Higgs self-coupling are fixed when we vary vh. It turns out that the existence of the atomic nuclei plays a crucial role to maximize the entropy. This is reminiscent of the anthropic principle, however it is required by the fundamental law in our case.

Eternal Higgs inflation and the cosmological constant problem

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 eld 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

Weak scale from the maximum entropy principle

The theory of multiverse and wormholes suggests that the parameters of the Standard Model are fixed in such a way that the radiation of the S 3 universe at the final stage Srad becomes maximum, which we call the maximum entropy principle. Although it is difficult to confirm this principle generally, for a few parameters of the Standard Model, we can check whether Srad actually becomes maximum at the observed values. In this paper, we regard Srad at the final stage as a function of the weak scale ( the Higgs expectation value ) vh, and show that it becomes maximum around vh = O(300GeV) when the dimensionless couplings in the Standard Model, that is, the Higgs self coupling, the gauge couplings, and the Yukawa couplings are fixed. Roughly speaking, we find that the weak scale is given by vh ∼ T 2 BBN Mply 5 ,

Flavor structure in D-brane models: Majorana neutrino masses

A bstractWe study the flavor structure in intersecting D-brane models. We study anomalies of the discrete flavor symmetries. We analyze the Majorana neutrino masses, which can be generated by D-brane instanton effects. It is found that a certain pattern of mass matrix is obtained and the cyclic permutation symmetry remains unbroken. As a result, trimaximal mixing matrix can be realized if Dirac neutrino mass and charged lepton mass matrices are diagonal.