arXiv subjects
Publications and source records attributed to Satoshi Takagi.
In this paper, we generalize the construction method of schemes to other algebraic categories, and show that the category of coherent schemes can be characterized by a universal property, if we fix the class of Grothendieck topology. Also, we introduce the notion of $\scr{C}$-schemes, which is a further generalization of coherent schemes and still shares common properties with ordinary schemes.
In this paper, we introduce a new algebraic type of `convexoid rings', and we give the definition of (weak) convexoid schemes, which share similar properties with ordinary schemes. As a result, we give a purely-algebraic construction of the compactification of Spec Z (in Arakelov's sense) which is realized as the Zariski-Riemann space in the category of weak convexoid schemes.
In this paper, we will investigate further properties of A-schemes. The category of A-schemes possesses many properties of the category of coherent schemes, and in addition, it is co-complete and complete. There is the universal compactification, namely, the Zariski-Riemann space in the category of A-schemes. We compare it with the conventional Zariski-Riemann space, and characterize the latter by a left adjoint.
We define the notion of normal A-schemes, and approximable A-schemes. Approximable A-schemes inherit many good properties of ordinary schemes. As a consequence, we see that the Zariski-Riemann space can be regarded in two ways -- either as the limit space of admissible blow ups, or as the universal compactification of the given non-proper scheme. We can prove Nagata embedding using Zariski-Riemann spaces.
In this paper, we give some categorical description of the general spectrum functor, defining it as an adjoint of a global section functor. The general spectrum functor includes that of $F_1$ and of semirings.
We investigate the phase structure of hot and/or dense QCD with massless 2-flavors using the Schwinger-Dyson equation (SDE) with the improved ladder approximation in the Landau gauge. We examine the effect of the antiquark contribution and find that setting the antiquark Majorana mass equal to the quark one is a good approximation in the medium density region. The imaginary part of the Dirac mass has an important influence on the chiral phase transition, in particular on the tricritical point.
We investigate the phase structure of hot and/or dense QCD using the Schwinger-Dyson equation (SDE) with the improved ladder approximation in the Landau gauge. We show that the phase transition from the two-flavor color superconducting (2SC) phase to the quark-gluon plasma (QGP) phase is of second order, and that the scaling properties of the Majorana mass gap and the diquark condensate are consistent with mean field scaling. We examine the effect of the antiquark contribution and find that setting the antiquark Majorana mass equal to the quark one is a good approximation in the medium density region. We also study the effect of the Debye screening mass of the gluon and find that ignoring it causes the critical lines to move to the region of higher temperature and higher chemical potential.
We investigate the phase structure of dense QCD using the Schwinger-Dyson equation (SDE) with the improved ladder approximation in the Landau gauge. We use the gluon propagator with the electric mode corrected by Debye screening and the magnetic mode corrected by Landau damping. We solve the coupled SDE for the Majorana masses of the quark and antiquark (separately from the SDE for the Dirac mass) in the low density and intermediate density regions. In the low density region, both the SDEs for the Majorana masses and the Dirac mass have nontrivial solutions that correspond to the color symmetry breaking (CSB) vacuum and the chiral symmetry breaking ($χ$SB) vacuum. Comparing the values of the effective potential in the two vacua, we show that the phase transition from the $χ$SB vacuum to the CSB vacuum is of first order. The resultant value of the critical chemical potential is about 210 MeV, which is smaller than that obtained from the SDE analysis including only the Dirac mass. The momentum dependences of the Majorana masses of the quark and antiquark are shown to be quite different, although the masses are of the same order.