Reconsideration of the Coleman's Baby Universe

We reconsider the Coleman's mechanism that solves the Cosmological Constant Problem by the baby universes. We use the Lorentzian path integral and allow each universe has a different effective field theory and a vacuum. By using the probability distribution of coupling constants, it is shown that the cosmological constant of our universe does not necessary become small due to the effects of other universes.Comment: 13 pages, 3 figures; typos are corrected, and references are added (v3

Criticality and Inflation of the Gauged B-L Model

We consider the multiple point principle (MPP) and the inflation of the gauged B-L extension of the Standard Model (SM) with a classical conformality. We examine whether the scalar couplings and their beta functions can become simultaneously zero at $\Lambda_{\text{MPP}}:=10^{17}$ GeV by using the two-loop renormalization group equations (RGEs). We find that we can actually realize such a situation and that the parameters of the model are uniquely determined by the MPP. However, as discussed in \cite{Iso:2012jn}, if we want to realize the electroweak symmetry breaking by the radiative B-L symmetry breaking, the self coupling $\lambda_{\Psi}$ of a newly introduced SM singlet complex scalar $\Psi$ must have a non-zero value at $\Lambda_{\text{MPP}}$, which means the breaking of the MPP. We find that the ${\cal{O}}(100)$GeV electroweak symmetry breaking can be achieved even if this breaking is very small; $\lambda_{\Psi}(\Lambda_{\text{MPP}})\leq10^{-10}$. Within this situation, the mass of the B-L gauge boson is predicted to be \begin{equation} M_{B-L}=2\sqrt{2}\times\sqrt{\frac{\lambda(v_{h})}{0.10}}\times v_{h}\simeq 696\hspace{1mm}\text{GeV},\nonumber\end{equation} where $\lambda$ is the Higgs self coupling and $v_{h}$ is the Higgs expectation value. This is a remarkable prediction of the (slightly broken) MPP. Furthermore, such a small $\lambda_{\Psi}$ opens a new possibility: $\Psi$ plays a roll of the inflaton \cite{Okada:2011en}. Another purpose of this paper is to investigate the $\lambda_{\Psi}\Psi^{4}$ inflation scenario with the non-minimal gravitational coupling $\xi\Psi^{2} {\cal{R}}$ based on the two-loop RGEs.Comment: 28 pages, 8 figures; some typos are corrected, Eq.(11) is corrected, the predicted mass of M_{B-L} has changed, RGEs are corrected, footnotes added, references added (v2); some typos are corrected, Eq.(26) is added, references added, version to appear in PTEP(v3

Measurement of electrons from charm and beauty hadron decays in p-Pb collisions at sNN=8.16 \sqrt{s_{\mathrm{NN}}} = 8.16\,TeV with ALICE

Lattice Quantum Chromodynamics (QCD) calculation predicts that a colour-deconfined QCD matter, Quark-Gluon Plasma (QGP), is formed at high temperature and energy density reached in ultra-relativistic heavy-ion collisions. Heavy quarks (charm and beauty) are mostly produced by initial hard scatterings before the formation of the QGP. Therefore heavy-flavour hadrons are ideal probes to investigate the properties of the hot and dense QCD matter. In Pb-Pb collisions, a strong suppression of the production of heavy-flavour hadrons with high transverse momentum has been observed. A deeper understanding of heavy-flavour production and interaction with the QGP requires detailed studies of Cold Nuclear Matter (CNM) effects in order to clarify the role of initial- and final-state effects on their production. CNM effects include shadowing and/or saturation of partons, energy loss in CNM and $k_{\rm{T}}$-broadening. Such effects on heavy quark production can be studied in proton-nucleus collisions via heavy-flavour decays electrons. High-$p_{\rm{T}}$ electrons are especially interesting because they mainly originate from beauty hadrons. We report the $p_{\rm{T}}$ dependence of the nuclear modification factor ($R_{\rm{pPb}}$) and ratio of cross section of heavy-flavour decays electrons in p-Pb collisions with different collision energies, $\sqrt{s_{\mathrm{NN}}} = 8.16\,$TeV and $\sqrt{s_{\mathrm{NN}}} = 5.02\,$TeV.Comment: 4 pages, 6 figures, Proceedings of 8th International Conference on Quarks and Nuclear Physics, Nov. 13-17, 201

Hillclimbing saddle point inflation

Recently a new inflationary scenario was proposed in arXiv:1703.09020 which can be applicable to an inflaton having multiple vacua. In this letter, we consider a more general situation where the inflaton potential has a (UV) saddle point around the Planck scale. This class of models can be regarded as a natural generalization of the hillclimbing Higgs inflation (arXiv:1705.03696).Comment: 5 pages, 3 figures; Report number added (v2

RG-improvement of the effective action with multiple mass scales

Improving the effective action by the renormalization group (RG) with several mass scales is an important problem in quantum field theories. A method based on the decoupling theorem was proposed in \cite{Bando:1992wy} and systematically improved \cite{Casas:1998cf} to take threshold effects into account. In this paper, we apply the method to the Higgs-Yukawa model, including wave-function renormalizations, and to a model with two real scalar fields $(\varphi, h)$. In the Higgs-Yukawa model, even at one-loop level, Feynman diagrams contain propagators with different mass scales and decoupling scales must be chosen appropriately to absorb threshold corrections. On the other hand, in the two-scalar model, the mass matrix of the scalar fields is a function of their field values $(\varphi, h)$ and the resultant running couplings obey different RGEs on a different point of the field space. By solving the RGEs, we can obtain the RG improved effective action in the whole region of the scalar fields.Comment: 22 pages, 6 figure

Reheating-era leptogenesis

We propose a novel leptogenesis scenario at the reheating era. Our setup is minimal in the sense that, in addition to the standard model Lagrangian, we only consider an inflaton and higher dimensional operators. The lepton number asymmetry is produced not by the decay of a heavy particle, but by the scattering between the standard model particles. After the decay of an inflaton, the model is described within the standard model with higher dimensional operators. The Sakharov's three conditions are satisfied by the following way. The violation of the lepton number is realized by the dimension-5 operator. The complex phase comes from the dimension-6 four lepton operator. The universe is out of equilibrium before the reheating is completed. It is found that the successful baryogenesis is realized for the wide range of parameters, the inflaton mass and reheating temperature, depending on the cutoff scale. Since we only rely on the effective Lagrangian, our scenario can be applicable to all mechanisms to generate neutrino Majorana masses.Comment: 5 pages, 3 figures; published version(v2

Saddle point inflation in string-inspired theory

The observed value of the Higgs mass indicates the possibility that there is no supersymmetry below the Planck scale and that the Higgs can play the role of the inflaton. We examine the general structure of the saddle point inflation in string-inspired theory without supersymmetry. We point out that the string scale is fixed to be around the GUT scale $\sim10^{16}$GeV in order to realize successful inflation. We find that the inflaton can be naturally identified with the Higgs field.Comment: 12 pages, 2 figures(v1); Version to appear on PTEP(v2

Landau pole in the Standard Model with weakly interacting scalar fields

We consider the Standard Model with a new scalar field $X$ which is a $n_X^{}$ 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 $n_X^{}\geq 4$. 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.Comment: 8 pages, 2 figures, 2 tables(v1); published version(v2