Kouji Nomura

Charmonium at finite temperature in quenched lattice QCD

We study charmonium correlators in pseudoscalar and vector channels at finite temperature using lattice QCD simulation in the quenched approximation. Anisotropic lattices are used in order to have sufficient numbers of degrees of freedom in the Euclidean temporal direction. We focus on the low energy structure of the spectral function, corresponding to the ground state in the hadron phase, by applying the smearing technique to enhance the contribution to the correlator from this region. We employ two analysis procedures: the maximum entropy method (MEM) for the extraction of the spectral function without assuming a specific form, to estimate the shape of the spectral function, and the standard χ2 fit analysis using typical forms in accordance with the result of MEM, for a more quantitative evaluation. To verify the applicability of the procedures, we first analyze the smeared correlators as well as the point correlators at zero temperature. We find that by shortening the t-interval used for the analysis (a situation inevitable at T>0) the reliability of MEM for point correlators is lost, while it subsists for smeared correlators. Then the smeared correlators at T≃ 0.9 Tc and 1.1 Tc are analyzed. At T≃ 0.9 Tc, the spectral function exhibits a strong peak, well approximated by a delta function corresponding to the ground state with almost the same mass as at T=0. At T≃ 1.1 Tc, we find that the strong peak structure still persists at almost the same place as below Tc, but with a finite width of a few hundred MeV. This result indicates that the correlators possess a nontrivial structure even in the deconfined phase. PACS: 12.38.Gc Lattice QCD calculations – 12.38.Mh Quark-gluon plasma

Circadian changes in arginine vasopressin level in the suprachiasmatic nuclei in the rat

Arginine vasopressin (AVP) neurons were preferentially localized in the dorsomedial part of the suprachiasmatic nucleus (SCN). To know the role of AVP neurons in the SCN, male rats were kept under a normal light-dark cycle (L-D), or under constant darkness (D-D) for 20 days. In L-D condition, AVP levels in the SCN showed the circadian change. In D-D condition, the patterns in AVP levels showed a free-running rhythm, and an about 12-h shift per 20 days. This result suggests that the activity of AVP neurons may be closely associated with the endogenous circadian rhythm of the SCN.

Maintenance of Estrous Cycle in Female Rats with Anterior or Posterior Deafferentation of the Suprachiasmatic Nucleus

The aim of the present study was to determine which of the anterior or posterior efferents of the suprachiasmatic nucleus (SCN) predominantly act for the maintenance of estrous cycle in female rats. A small knife (0.8 mm in radius) was used for anterior (ASD), posterior (PSD) and complete suprachiasmatic deafferentations (CSD). The rats subjected to CSD were divided into two groups, the first group bearing lesions on the medial preoptic nucleus (MPN; group CSD-MPN-L) and the other group bearing no lesions on the MPN (group CSD). For reference, anterior hypothalamic deafferentation (AHD) was carried out using a large knife (2.0 mm in radius). All rats with AHD or CSD-MPN-L and some of CSD rats showed persistent estrus, but all animals with ASD or PSD resumed regular estrous cycles after transient irregular periods. Ovaries of AHD, CSD and CSD-MPN-L rats contained very few, if any, corpora lutea, while the number of corpora lutea in ASD or PSD rats was not significantly different from that of sham-operated controls. Immunohistochemical examination revealed that in AHD rats LHRH immunoreactivity in the median eminence was markedly reduced as compared with that of sham-operated controls. In contrast, in ASD, PSD, CSD and CSD-MPN-L rats, the LHRH immunoreactivity in the median eminence was similar to that of sham-operated controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Charmonium near the deconfining transition on the lattice

Abstract We study the charmonium properties at finite temperature using quenched lattice QCD simulations. Although a simple potential model analysis indicates no bound state at T > 1.05Tc, our analyses of the spatial correlation between quark and anti-quark and the spectral function indicate that a bound-state-like structure may survive even above Tc.

Luteinizing hormone-releasing hormone (LHRH) neurons in the male and female rats at peripubertal period

SummaryLuteinizing hormone-releasing hormone (LHRH) neurons were immunohistochemically studied in rats of both sexes at peripubertal ages. The number of immunoreactive LHRH neurons (irLHRH neurons) was counted in the brain region from the level of the septumpreoptic area to the level of the rostral part of the infundibulum in colchicine-treated male and female rats at 30 and 60 days of age. At 30 days, irLHRH neurons were more numerous in male rats than females. At 60 days, the number of irLHRH neurons in female rats increased to the level of male rats of the same age. In non-colchicine-treated rats, the count of irLHRH neuron was quite low. The difference in the number of irLHRH neurons between colchicine-treated and non-treated rats may be regarded as the activity of LHRH system. The difference in the number of irLHRH neurons was larger in male rats than in female rats at 30 days of age. On the contrary, at 60 days of age, the difference was larger in females than in males. LHRH contents were measured in the preoptic-anterior hypothalamic area (POA-AH), where LHRH neuronal perikarya are mainly located, and in the mid-hypothalamic area. LHRH content of the POA-AH in male rats at 60 days of age was not significantly different from that at 30 days of age. While, LHRH content in the POA-AH was greater in 60-day-old female rats at proestrous morning than that in 30-day-old females. At 30 days of age, male rats tended to contain more LHRH in the POA-AH than female rats. However, either at 30 days or at 60 days, no statistically significant differences were detected between male and female rats. In mid-hypothalamic area, LHRH content in 60-day-old male rats was greater than that in 30-day-old male rats. On the other hand, there was no difference in LHRH content between 30-day-old and 60-day-old female rats. At 60 days of age, LHRH content in male rats was greater than that in female rats. The present morphological findings and LHRH measurements suggest that the functional maturation of LHRH system occurred earlier in male rats than in female rats.

CHARMONIUM CORRELATORS AT FINITE TEMPERATURE IN QUENCHED LATTICE QCD

We study charmonium correlators at finite temperature using quenched lattice QCD simulations. Two analysis procedures are applied to extract information on the spectral function: the maximum entropy method, and the �2 fit analyses including the constrained curve fitting. We focus on the low energy structure of the spectral function by applying the smearing technique. We first discuss the applicability of these methods to the finite temperatures by analyzing the data at T = 0 with restricted numbers of degrees of freedom. Then we apply these methods to the correlators at T > 0. We find no indication of mass shift and finite width for the charmonium states at T ≃ 0.9Tc. The results at T ≃ 1.1Tc imply that bound-state-like structures may survive even above Tc.

Numerical study of staggered fermion on anisotropic lattices

Abstract We study calibration procedures of the staggered quarks on anisotropic lattices in the quenched approximation and in N f = 2 dynamical simulations. For the calibration conditions we adopt the hadronic radii r 0 and the meson masses in the temporal and spatial directions. On the quenched lattice, we calibrate the quark field and compare the result with the result determined using the meson dispersion relation. In dynamical simulations, we determine the anisotropy parameters γ G and γ F simultaneously within 1% accuracy at renormalized anisotropy ξ = a s a t =4 .

Numerical Study of the Staggered Quark Action on Quenched Anisotropic Lattices

The staggered quark action on anisotropic lattices is studied. We carried out numerical simulations under the quenched approximation for three values of the lattice spacing (a −1 =1 – 2 GeV) with the anisotropy ξ = aσ/aτ = 4, where aσ and aτ are the spatial and temporal lattice spacings, respectively. The bare anisotropy γF in the quark action was numerically tuned in two separate ways, by adjusting the ratio of the meson masses in the fine and coarse directions, and by adjusting the meson dispersion relation, so that the renormalized fermionic anisotropy coincided with that of the gauge field. The discrepancy obtained using these two calibration schemes provides an estimate of the finite lattice artifact, which is found to be sizable in the range of cutoff values explored in this work. We also computed the meson masses using correlators with a wall source, employing the tuned value of the anisotropy parameter. We find that the flavor symmetry breaking effect smoothly decreases as β increases. The effect of the uncertainty in γF on the meson masses is examined. We also discuss the outlook for dynamical simulations.

Study of spatial meson correlators at finite temperature in quenched anisotropic lattice QCD

Abstract We analyze the meson correlator in the spatial direction at finite temperature. To achieve fine resolution in the spatial direction, we use an anisotropic lattice with the standard Wilson plaquette gauge action and the O ( a ) improved Wilson quark action. Below and above T c , properties of correlators are investigated by two methods: fits with ansatz for the spectral function, and direct reconstruction of the spectral function using the maximum entropy method.

Light meson correlation functions near the deconfining transition on anisotropic lattices

Abstract We study the light hadron correlators near the deconfining transition by extracting the spectral function on quenched anisotropic lattices. We adopt the method successfully applied to the charmonium systems: the use of the smeared operators and the analysis method which is composed of the maximum entropy method and the χ 2 fitting assuming several forms. The numerical simulations are performed on lattices of a s −2 ≅ 2 GeV and a s / a t = 4, with the clover quark around the strange quark mass. Towards applications to the plasma phase, we check the reliability of our procedure by examining how the results for the correlators below T c ( N t = 32) changes under variation of input parameters such as the smearing function.