arXiv subjects

Masatoshi Sato

Publications and source records attributed to Masatoshi Sato.

211 records · Page 12Linked to original sources

arXiv2000

Mechanism of spin-triplet superconductivity in Sr2RuO4

The unique Fermi surfaces and their nesting properties of Sr2RuO4 are considered. The existence of unconventional superconductivity is shown microscopically, for the first time, from the magnetic interactions (due to nesting) and the phonon-mediated interactions. The odd-parity superconductivity is favored in the $α$ and $β$ sheets of the Fermi surface, and the various superconductivities are possible in the $γ$ sheet. There are a number of possible odd-parity gaps, which include the gaps with nodes, the breaking of time-reversal symmetry and $\vec{d}\parallel \hat{z}$.

cond-mat.supr-con↗

arXiv2000

Spin-triplet superconductivity in quasi-one dimension

We consider a system with electron-phonon interaction, antiferromagnetic fluctuations and disconnected open Fermi surfaces. The existence of odd-parity superconductivity in this circumstance is shown for the first time. If it is applied to the quasi-one-dimensional systems like the organic conductors (TMTSF)_2X we obtain spin-triplet superconductivity with nodeless gap. Our result is also valid in higher dimensions(2d and 3d).

cond-mat.supr-con↗

arXiv1998

Valley Views: Instantons, Large Order Behaviors, and Supersymmetry

The elucidation of the properties of the instantons in the topologically trivial sector has been a long-standing puzzle. Here we claim that the properties can be summarized in terms of the geometrical structure in the configuration space, the valley. The evidence for this claim is presented in various ways. The conventional perturbation theory and the non-perturbative calculation are unified, and the ambiguity of the Borel transform of the perturbation series is removed. A `proof' of Bogomolny's ``trick'' is presented, which enables us to go beyond the dilute-gas approximation. The prediction of the large order behavior of the perturbation theory is confirmed by explicit calculations, in some cases to the 478-th order. A new type of supersymmetry is found as a by-product, and our result is shown to be consistent with the non-renormalization theorem. The prediction of the energy levels is confirmed with numerical solutions of the Schrödinger equation.

hep-th↗

arXiv1997

Valleys in Quantum Mechanics

Conventionally, perturbative and non-perturbative calculations are performed independently. In this paper, valleys in the configuration space in quantum mechanics are investigated as a way to treat them in a unified manner. All the known results of the interplay of them are reproduced naturally. The prescription for separating the non-perturbative contribution from the perturbative is given in terms of the analytic continuation of the valley parameter. Our method is illustrated on a new series of examples with the asymmetric double-well potential. We obtain the non-perturbative part explicitly, which leads to the prediction of the large order behavior of the perturbative series. We calculate the first 200 perturbative coefficients for a wide range of parameters and confirm the agreement with the prediction of the valley method.

quant-ph↗

arXiv1997

Recent Developments in the Theory of Tunneling

Path-integral approach in imaginary and complex time has been proven successful in treating the tunneling phenomena in quantum mechanics and quantum field theories. Latest developments in this field, the proper valley method in imaginary time, its application to various quantum systems, complex time formalism, asympton theory for the large order analysis of the perturbation theory, are reviewed in a self-contained manner.

hep-th↗

arXiv1997

Electroweak baryon and lepton number violating processes at high energies by the valley instanton

We calculate the cross sections of the baryon and lepton number violating processes. The proper valley method enables us to calculate the multi-boson processes, which have the possibility to observation. The mass corrections of the gauge boson, Higgs particle and top quark are evaluated and the group integration and the phase space integration are performed analytically and numerically.

hep-ph↗

arXiv1996

Multi-instanton calculus versus exact results in N=2 supersymmetric QCD

Microscopic tests of the exact results are performed in $N=2$ supersymmetric $SU(2)$ QCD. We present the complete construction of the multi-instanton in $N=2$ supersymmetric QCD. All the defining equations of the super instanton are reduced to the algebraic equations. Using this result, we calculate the two-instanton contribution ${\cal F}_2$ to the prepotential ${\cal F}$ for the arbitrary $N_f$ theories. For $N_f=0,1,2$, instanton calculus agrees with the prediction of the exact results, however, for $N_f=3,4$, we find discrepancies between them. We propose improved curves of the exact results for the massive $N_f=3$ and massless $N_f=4$ theories.

hep-th↗

arXiv1996

Multi-instanton calculus in N=2 supersymmetric QCD

Microscopic tests of the exact results are performed in N=2 SU(2) supersymmetric QCD. We construct the multi-instanton solution in N=2 supersymmetric QCD and calculate the two-instanton contribution ${\cal F}_2$ to the prepotential ${\cal F}$ explicitly. For $N_f=1,2$, instanton calculus agrees with the prediction of the exact results, however, for $N_f=3$, we find a discrepancy between them.

hep-th↗

arXiv1996

Fake Instability in the Euclidean Formalism

We study the path-integral formalism in the imaginary-time to show its validity in a case with a metastable ground state. The well-known method based on the bounce solution leads to the imaginary part of the energy even for a state that is only metastable and has a simple oscillating behavior instead of decaying. Although this has been argued to be the failure of the Euclidean formalism, we show that proper account of the global structure of the path-space leads to a valid expression for the energy spectrum, without the imaginary part. For this purpose we use the proper valley method to find a new type of instanton-like configuration, the ``valley instantons''. Although valley instantons are not the solutions of equation of motion, they have dominant contribution to the functional integration. A dilute-gas approximation for the valley instantons is shown to lead to the energy formula. This method extends the well-known imaginary-time formalism so that it can take into account the global behavior of the theory.

hep-th↗

arXiv1995

Valley Instanton versus Constrained Instanton

Based on the new valley equation, we propose the most plausible method for constructing instanton-like configurations in the theory where the presence of a mass scale prevents the existence of the classical solution with a finite radius. We call the resulting instanton-like configuration as valley instanton. The detail comparison between the valley instanton and the constrained instanton in $ϕ^4$ theory and the gauge-Higgs system are carried out. For instanton-like configurations with large radii, there appear remarkable differences between them. These differences are essential in calculating the baryon number violating processes with multi bosons.

hep-th↗

arXiv1995

Shapes of Cosmic Strings and Baryon Number Violation

The relation between shapes of cosmic string and baryon number violation is investigated. If there exist fermionic zero modes on the string, using bosonization technique, it is possible to obtain the effective action which describes the fermion coupled to the arbitrarily shaped cosmic string. The relation between baryon number and the sum of the writhing number and linking number of the cosmic strings is rederived. Baryons are created on the strings as the shapes of the cosmic strings change. Furthermore we discuss implications of this baryon number violating process to baryogenesis.

hep-ph↗

arXiv1995

Valley Instanton in the Gauge-Higgs System

The instanton configuration in the SU(2)-gauge system with a Higgs doublet is constructed by using the new valley method. This method defines the configuration by an extension of the field equation and allows the exact conversion of the quasi-zero eigenmode to a collective coordinate. It does not require ad-hoc constraints used in the current constrained instanton method and provides a better mathematical formalism than the constrained instanton method. The resulting instanton, which we call ``valley instanton'', is shown to have desirable behaviors. The result of the numerical investigation is also presented.

hep-th↗

arXiv1994

"Topological" Formulation of Effective Vortex Strings

We present a ``topological'' formulation of arbitrarily shaped vortex strings in four dimensional field theory. By using a large Higgs mass expansion, we then evaluate the effective action of the closed Abrikosov-Nielsen-Olesen vortex string. It is shown that the effective action contains the Nambu-Goto term and an extrinsic curvature squared term with negative sign. We next evaluate the topological $\FtF$ term and find that it becomes the sum of an ordinary self-intersection number and Polyakov's self-intersection number of the world sheet swept by the vortex string. These self-intersection numbers are related to the self-linking number and the total twist number, respectively. Furthermore, the $\FtF$ term turns out to be the difference between the sum of the writhing numbers and the linking numbers of the vortex strings at the initial time and the one at the final time. When the vortex string is coupled to fermions, the chiral fermion number of the vortex string becomes the writhing number (modulo $\bZ$) through the chiral anomaly. Our formulation is also applied to ``global'' vortex strings in a model with a broken global $U(1)$ symmetry.

hep-th↗