Search

The nuclear matrix element (NME) of the neutrinoless double-$\beta$ ($0\nu\beta\beta$) decay is an essential input for determining the neutrino effective mass, if the half-life of this decay is measured. The reliable calculation of this NME has been a long-standing problem because of the diversity of the predicted values of the NME depending on the calculation method. In this paper, we focus on the shell model and the QRPA. The shell model have a rich amount of the many-particle many-hole correlations, and the QRPA can obtain the convergence of the result of calculation with respect to the extension of the single-particle space. It is difficult for the shell model to obtain the convergence of the $0\nu\beta\beta$ NME with respect to the valence single-particle space. The many-body correlations of the QRPA are insufficient depending on nuclei. We propose a new method to modify phenomenologically the results of the shell model and the QRPA compensating the insufficient point of each method by using the information of other method complementarily. Extrapolations of the components of the $0\nu\beta\beta$ NME of the shell model are made toward a very large valence single-particle space. We introduce a modification factor to the components of the $0\nu\beta\beta$ NME of the QRPA. Our modification method gives similar values of the $0\nu\beta\beta$ NME of the two methods for $^{48}$Ca. The NME of the two-neutrino double-$\beta$ decay is also modified in a similar but simpler manner, and the consistency of the two methods is improved., Comment: 21 pages, 4 figures, section VII was modified

A new method has been proposed to determine the strength of the isoscalar proton-neutron pairing interaction applicable to many nuclei. The principle is the equivalence between the double-charge change and the double transfer of like-particle pairs, and a constraint is derived for the effective interactions used in approximations. This method was applied to the quasiparticle random-phase approximation for determining that interaction strength. In this paper, details of this method are explained thoroughly, and applications to nuclei of several instances of the double-$\ensuremath{\beta}$ decays are shown. The systematics of the strengths determined for those nuclei is understood in terms of a midshell effect. The effect of the new interaction strength is examined in two examples of the Gamow-Teller strength function with comparisons with the experimental data. The nuclear matrix elements of the neutrinoless double-$\ensuremath{\beta}$ decay are also calculated.

We have proposed in a series of previous papers a method to determine the effective axial-vector current coupling and the strength of the isoscalar proton-neutron pairing interaction for calculating the nuclear matrix elements of the neutrinoless double-$\beta$ decay by the quasiparticle random-phase approximation. The combination of these two parameters have had an uncertainty in this approach, but now this uncertainty is removed. In this paper, we apply our method to the neutrinoless double-$\beta$ decays of $^{136}$Xe and $^{130}$Te and predict the nuclear matrix elements and reduced half-lives. Our calculation is tested first by a self-check method using the two-neutrino double-$\beta$ decay, and this test ensures the application of our method to $^{136}$Xe. It turns out, however, that our method is not successful in $^{130}$Te. Further test is made for our calculation of the $\beta$ decay of $^{138}$Xe, and a satisfactory result is obtained.

We investigate the reliability of the quasiparticle random-phase approximation (QRPA) in application to the nuclear matrix element (NME) of the double-β decay of 136Xe. We examine the dependence of the NME of the two-neutrino double-β (2νββ) decay on the choice of the set of the intermediate-state energies, spectrum of the intermediate nucleus, the Gamow-Teller (GT) strength distribution, the GT strengths of the β decays of a nearby nucleus, and a higher-order term of the 2νββ NME recently proposed. The QRPA approach is a good approximation to the decay instance of 136Xe → 136Ba.We investigate the reliability of the quasiparticle random-phase approximation (QRPA) in application to the nuclear matrix element (NME) of the double-β decay of 136Xe. We examine the dependence of the NME of the two-neutrino double-β (2νββ) decay on the choice of the set of the intermediate-state energies, spectrum of the intermediate nucleus, the Gamow-Teller (GT) strength distribution, the GT strengths of the β decays of a nearby nucleus, and a higher-order term of the 2νββ NME recently proposed. The QRPA approach is a good approximation to the decay instance of 136Xe → 136Ba.

The nuclear matrix elements (NMEs) of the neutrinoless and two-neutrino double-$\ensuremath{\beta}$ decays of $^{48}\mathrm{Ca}$ are calculated by the quasiparticle random-phase approximation (QRPA) with emphasis on the consistency examinations of this calculation method. The main new examination points are the consistency of two ways to treat the intermediate-state energies in the two-neutrino double-$\ensuremath{\beta}$ NME and comparison with the experimental charge-exchange strength functions obtained from $^{48}\mathrm{Ca}(p,n)$ and $^{48}\mathrm{Ti}(n,p)$ reactions. No decisive problem preventing use of the QRPA approach is found. The obtained neutrinoless double-$\ensuremath{\beta}$ NME adjusted by the ratio of the effective and bare axial-vector current couplings is lowest in those calculated by different groups and close to one of the QRPA values obtained by another group.

We show the formulation and the result of test calculation of the overlap of excites states in the quasiparticle random-phase approximation for calculating the nuclear matrix elements of the neutrino-less double beta decay. Our method uses the ground states of the QRPA explicitly. The feasibility of that calculation is demonstrated, and the effectiveness of the truncation used in our method is shown.

The UNEDF project was a large-scale collaborative effort that applied high-performance computing to the nuclear quantum many-body problem. The primary focus of the project was on constructing, validating, and applying an optimized nuclear energy density functional, which entailed a wide range of pioneering developments in microscopic nuclear structure and reactions, algorithms, high-performance computing, and uncertainty quantification. UNEDF demonstrated that close associations among nuclear physicists, mathematicians, and computer scientists can lead to novel physics outcomes built on algorithmic innovations and computational developments. This review showcases a wide range of UNEDF science results to illustrate this interplay.

We show that the correlations of the quasiparticle random-phase approximation (QRPA) significantly reduce the nuclear matrix element (NME) of neutrinoless double-beta decay by a new mechanism in the calculation for $^{150}$Nd $\rightarrow$ $^{150}$Sm. This effect is due mainly to the normalization factors of the QRPA ground states included in the overlap of intermediate states, to which the QRPA states based on the initial and final ground states are applied. These normalization factors arise according to the definition of the QRPA ground state as the vacuum of quasibosons. Our NME is close to those of other groups in spite of this new reduction effect because we do not use the proton-neutron pairing interaction usually used for reproducing the experimental NME of the two-neutrino double-beta ($2\nu\beta\beta$) decay. Our method can repeoduce the experimental $2\nu\beta\beta$ NME for $^{150}$Nd $\rightarrow$ $^{150}$Sm with the quenching axial-vector current coupling without approacing the breaking point of the QRPA. The consistency of QRPA approaches taking different virtual paths under the closure approximation is also discussed, and an extension of the QRPA ground state is proposed., Comment: 15 pages, 7 figures, calculation corrected, a new section added

We calculate energies E 2 + and transition strengths B ( E 2 ) ↑ of the lowest 2 + states of even Te, Sn and Ni isotopes in a neutron-rich region, using quasiparticle random phase approximation with simple separable type interactions. With those calculations reproducing the experimental systematics very well, we discuss, first, an unusual relation of E 2 + and B ( E 2 ) ↑ of 132, 136 Te isotopes, which does not follow an empirical formula B ( E 2 ) ↑ ∝ 1 / E 2 + . Second, B ( E 2 ) ↑ of 132 Sn is discussed which is larger than those of the neighboring even Sn. This is a phenomenon confirmed by an experiment very recently. Third, we point out that the small B ( E 2 ) ↑ of 68 Ni is due to fragmentation of the transition strength into some excited states in a low-energy region.

Background: Although it is well-known that plasma glucose concentration ((G) p ) decreases during hemodialysis, the precise mechanism underlying this decrease has not yet been fully elucidated. The aim of the present study was to investigate the mechanism underlying hemodialysis-induced decrease (HID) in (G) p during the dialysis in vivo or in vitro. Methods: Using high CO 2 / HCO 3 dialysate, we measured (G) p by a hexose kinase method ((G) pHK ) and concentrations of electrolytes, as well as pH, PCO 2 and PO 2 for both plasma and dialysate samples at pre- and postdialyzer sites obtained from hemodialysis patients with nondiabetic chronic renal failure (CRF). Furthermore, we studied the effect of PCO 2 and acetazolamide (ACZ) on the changes in (G) pHK during the dialysis in vitro. Results: After the first dialysis of CRF patients, the (G) pHK decreased from 118.3 ± 18.0 to 98.6 ± 5.7 mg/dl (p < 0.05), the latter value being significantly lower than glucose concentration in dialysate samples (approximately 105 mg/dl) at predialyzer sites. In the experiments of blood samples from healthy volunteers, (G) pHK decreased significantly after elevating or lowering CO 2 level in the dialysates. In contrast, when the difference in PCO 2 between the blood and dialysate was reduced, the HID in (G) pHK was abolished during hemodialysis. The addition of 10 -4 M ACZ to the blood samples completely prevented the development of HID in (G) pHK caused by the perfusion of high or low CO 2 /HCO 3 - dialysates. Conclusions: During hemodialysis using high CO 2 /HCO 3 - dialysate, the HID in (G) p results from the diffusion of glucose from plasma into erythrocytes, probably due to the consumption of glucose resulting from the accelerated anaerobic metabolism induced by the changes in the cytoplasmic pH of erythrocytes.

Nuclear life in neutron-rich and proton-rich Terra Incognita is different from that around the stability line; the promised access to completely new combinations of proton and neutron numbers offers prospects for new structural phenomena. The main objective of this talk is to discuss some of the theoretical challenges and opportunities for nuclear structure research with new electro-magnetic isotope separators.

We present two new ideas on the quasiparticle random-phase approximation (QRPA) approach for calculating nuclear matrix elements of double-beta decay. First, it is necessary to calculate overlaps of the QRPA states obtained on the basis of the ground states of different nuclei. We calculate this overlap using quasiboson vacua as the QRPA ground states. Second, we show that two-particle transfer paths are possible to use for the calculation under the closure approximation. A calculation is shown for 150Nd→150Sm using these two new ideas, and their implication is discussed.

We investigate the role the interweaving of surface vibrations and nucleon motion has on Cooper pair formation in spherical superfluid nuclei. A quantitative calculation of the state-dependent pairing gap requires to go beyond the quasiparticle approximation, treating in detail the breaking of the single-particle strength and of the associated poles. This is done solving self-consistently the Dyson equation, including both a bare nucleon-nucleon interaction (which for simplicity we choose as a monopole-pairing force of constant matrix elements g) and an induced interaction arizing from the exchange of vibrations (calculated microscopically in QRPA) between pairs of nucleons moving in time reversal states. Both the normal and anomalous density Green functions are included, thus treating self-energy and pairing processes on equal footing. We apply the formalism to the superfluid nucleus 120Sn. Adjusting the value of g so as to reproduce, for levels close to the Fermi level, the empirical odd-even mass difference (Delta approx 1.4 MeV), it is found that the pairing gap receives about equal contributions from the monopole-pairing force and from the induced interaction. [More sentences continue. See the main body.], Comment: 15 pages, 4 figures, to be published in Nucl.Phys.A

It is shown that the random-phase approximation (RPA) method with its nonlinear generalization, which was previously considered as approximation, reproduces the exact solutions of the Lipkin model. The nonlinear RPA is based on an equation nonlinear on eigenvectors and includes many-particle-many-hole components in the creation operator of the excited states. We demonstrate the exact character of solutions analytically for the particle number $N$ = 2 and, numerically, for $N$ = 20. This finding indicates that the nonlinear RPA is equivalent to the exact Schr\"{o}dinger equation, which opens up new possibilities for realistic calculations in many-body problems., Comment: 17 pages, 9 figures

There are many indications which testify to the fact that the atomic nucleus can be viewed as a spherical little ball, which can also become football-shaped and plate-shaped, filled of a superfluid Fermi liquid resulting from the condensation of Cooper pairs build out of pairs of nucleons coupled to angular momentum zero. While the transition between the normal and the superfluid phases is not expected to be, in the case of the atomic nucleus, sharp as in the case of systems with an infinitely large number of particles, the analogies which can be drawn between the behaviour of the N→∞ systems and of the atomic nucleus are found to be very much to the point, once the effects of fluctuations are taken into account. In this paper we concentrate our attention on the consequences broken symmetry has on the energy level spectrum of superfluid atomic nuclei, and on its similarities and differences with respect to the N→∞ system. Results from both theory and experiment emphasize the common origin and conceptual affinity of some of the basic phenomena associated with spontaneous symmetry breaking, like the existence of zero frequency modes. Because the atomic nucleus can be viewed as the paradigm of finite many-body fermion systems, these results may also be of relevance in the study of other finite quantal systems like metal clusters, fullerenes, quantum dots, etc.

The induced pairing interaction arising from the exchange of low-lying collective surface vibrations among nucleons moving in time reversal states close to a Fermi energy is found to lead to values of the pairing gap which constitute a large fraction of those experimentally observed.

Quasiparticle random-phase approximation (QRPA) is applied to two nuclei, and overlap of the QRPA excited states based on the different nuclei is calculated. The aim is to calculate the overlap of intermediate nuclear states of the double-beta decay. We use the like-particle QRPA after the closure approximation is applied to the nuclear matrix elements. The overlap is calculated rigorously by making use of the explicit equation of the QRPA ground state. The formulation of the overlap is shown, and a test calculation is performed. The effectiveness of the truncations used is shown., 3 minor corrections and 1 minor change

Although nuclear energy-density functionals are determined primarily by fitting to ground-state properties, they are often applied in nuclear astrophysics to excited states, usually through the quasiparticle random-phase approximation (QRPA). Here we test the Skyrme functionals SkM${}^{*}$ and SLy4 along with the self-consistent QRPA by calculating properties of low-lying vibrational states in a large number of well-deformed even-even rare-earth nuclei. We reproduce trends in energies and transition probabilities associated with $\ensuremath{\gamma}$-vibrational states, but our results are not perfect and indicate the presence of multiparticle-hole correlations that are not included in the QRPA. The Skyrme functional SkM${}^{*}$ performs noticeably better than SLy4. In a few nuclei, changes in the treatment of the pairing energy functional have a significant effect. The QRPA is less successful with ``$\ensuremath{\beta}$-vibrational'' states than with the $\ensuremath{\gamma}$-vibrational states.

A microscopic calculation of reaction cross sections for nucleon-nucleus scattering has been performed by explicitly coupling the elastic channel to all particle-hole excitations in the target and one-nucleon pickup channels. The particle-hole states may be regarded as doorway states through which the flux flows to more complicated configurations, and subsequently to long-lived compound nucleus resonances. Target excitations for $^{40,48}$Ca, $^{58}$Ni, $^{90}$Zr and $^{144}$Sm were described in a random-phase framework using a Skyrme functional. Reaction cross sections obtained agree very well with experimental data and predictions of a state-of-the-art fitted optical potential. Couplings between inelastic states were found to be negligible, while the pickup channels contribute significantly. The effect of resonances from higher-order channels was assessed. Elastic angular distributions were also calculated within the same method, achieving good agreement with experimental data. For the first time observed absorptions are completely accounted for by explicit channel coupling, for incident energies between 10 and 70 MeV, with consistent angular distribution results., Comment: 13 pages, 9 figures. Version of paper accepted on December 1, 2011, for publication in Phys. Rev. C, following work on Phys. Rev. Lett. 105, 202502 (2010)

A microscopic calculation of the reaction cross-section for nucleon-nucleus scattering has been performed by explicitly coupling the elastic channel to all particle-hole (p-h) excitation states in the target and to all one-nucleon pickup channels. The p-h states may be regarded as doorway states through which the flux flows to more complicated configurations, and subsequently to long-lived compound nucleus resonances. Target excitations for 40,48Ca, 58Ni, 90Zr and 144Sm were described in a QRPA framework using a Skyrme functional. Reaction cross sections calculated in this approach were compared to predictions of a fitted optical potential and to experimental data, reaching very good agreement. Couplings between inelastic states were found to be negligible, while the couplings to pickup channels contribute significantly. For the first time observed reaction cross-sections are completely accounted for by explicit channel coupling, for incident energies between 10 and 40 MeV., Comment: Accepted for publication on Physical Review Letters. Article is expected to be published in the November 12, 2010 issue. 4 pages, 4 figures

We describe a new implementation of the quasiparticle random-phase approximation (QRPA) in axially symmetric deformed nuclei with Skyrme and volume-pairing energy-density functionals. After using a variety of tests to demonstrate the accuracy of the code in $^{24,26}\mathrm{Mg}$ and $^{16}\mathrm{O}$, we report the first fully self-consistent application of the Skyrme QRPA to a heavy deformed nucleus, calculating strength distributions for several ${K}^{\ensuremath{\pi}}$ in $^{172}\mathrm{Yb}$. We present energy-weighted sums, properties of $\ensuremath{\gamma}$-vibrational and low-energy ${K}^{\ensuremath{\pi}}={0}^{+}$ states, and the complete isovector $E1$ strength function. The QRPA calculation reproduces the properties of the low-lying ${2}^{+}$ states as well or better than it typically does in spherical nuclei.

We use the quasiparticle random-phase approximation (QRPA) and the Skyrme interactions $\mathrm{SLy}4$ and ${\mathrm{SkM}}^{*}$ to systematically calculate energies and transition strengths for the lowest ${2}^{+}$ state in spherical even-even nuclei. The ${\mathrm{SkM}}^{*}$ functional, applied to 178 spherical nuclei between $Z=10$ and 90, produces excitation energies that are on average 11% higher than experimental values, with residuals that fluctuate about the average by $\ensuremath{-}35%$ to $+55%$. The predictions of ${\mathrm{SkM}}^{*}$ and $\mathrm{SLy}4$ have significant differences, in part because of differences in the calculated ground state deformations; ${\mathrm{SkM}}^{*}$ performs better in both the average and dispersion of energies. Comparing the QRPA results with those of generator-coordinate-method (GCM) calculations, we find that the QRPA reproduces trends near closed shells better than the GCM, and that it overpredicts the energies less severely in general.

We calculate densities of excited states in the quasiparticle random-phase approximation (QRPA) with Skyrme interactions and volume pairing. We focus on low-energy peaks/bumps in the strength functions of a range of Ca, Ni, and Sn isotopes for J{sup {pi}}=0{sup +},1{sup -}, and 2{sup +}. We define an 'emitted-neutron number', which we then use to distinguish localized states from scattering-like states. The degree of delocalization either increases as the neutron-drip line is approached or stays high between the stability line and the drip line. In the 2{sup +} channel of Sn, however, the low-lying states, not even counting surface vibrations, are still fairly well localized on average, even at the neutron drip line.

Variation after particle-number restoration is incorporated for the first time into the Hartree-Fock-Bogoliubov (HFB) framework employing the Skyrme energy density functional with zero-range pairing. The resulting projected HFB equations can be expressed in terms of the local gauge-angle-dependent densities. Results of projected calculations are compared with those obtained within the Lipkin-Nogami method in the standard version and with the Lipkin-Nogami method followed by exact particle-number projection.

The phenomena of giant halo and halo of neutron-rich even-Ca isotopes are investigated and compared in the frameworks of the relativistic continuum Hartree-Bogoliubov (RCHB) and non-relativistic Skyrme Hartree-Fock-Bogoliubov (HFB) calculations. With two parameter sets for each of the RCHB and the Skyrme HFB calculations, it is found that although halo phenomena exist for Ca isotopes near neutron drip line in both calculations, the halo of the Skyrme HFB calculations starts at a more neutron-rich nucleus than that of the RCHB calculations, and the RCHB calculations have larger neutron root-mean-square (rms) radii systematically in N{>=}40 than those of the Skyrme HFB calculations. The former difference comes from the difference in shell structure. The reasons for the latter can be partly explained by the neutron 3s{sub 1/2} orbit, causes more than 50% of the difference among the four calculations for neutron rms radii at {sup 66}Ca.

We use the quasiparticle random phase approximation with a few Skyrme density functionals to calculate strength functions in the Jpi = 0+, 1-, and 2+ channels for even Ca, Ni, and Sn isotopes, from the proton drip line to the neutron drip line. We show where and how low-lying strength begins to appear as N increases. We also exhibit partial energy-weighted sums of the transition strength as functions of N for all nuclei calculated, and transition densities for many of the interesting peaks. We find that low-energy strength increases with N in all multipoles, but with distinctive features in each. The low-lying 0+ strength near the neutron at large N barely involves protons at all, with the strength coming primarily from a single two-quasineutron configuration with very large spatial extent. The low-lying 1- strength is different, with protons contributing to the transition density in the nuclear interior together with neutrons at large radii. The low-lying 2+ transition strength goes largely to more localized states. The three Skyrme interactions we test produce similar results, differing most significantly in their predictions for the location of the neutron drip line, the boundaries of deformed regions, energies of and transition strengths to the lowest 2+ states between closed shells, and isovector energy-weighted sum rules., 43 pages, 48 figures, 1 table

We use the canonical Hartree-Fock-Bogoliubov basis to implement a completely self-consistent quasiparticle-random-phase approximation with arbitrary Skyrme energy density functionals and density-dependent pairing functionals. The point of the approach is to accurately describe multipole strength functions in spherical even-even nuclei, including weakly-bound drip-line systems. We describe the method and carefully test its accuracy, particularly in handling spurious modes. To illustrate our approach, we calculate isoscalar and isovector monopole, dipole, and quadrupole strength functions in several Sn isotopes, both in the stable region and at the drip lines., 19 pages, 6 figures

Particle‐number restoration before variation is implemented in the HFB method employing the Skyrme force and contact delta pairing. Results are compared with those obtained within the Lipkin‐Nogami method, with or without the particle‐number projection after variation.

We calculate the B(E2) strength in 68Ni and other nickel isotopes using several theoretical approaches. We find that in 68Ni the gamma transition to the first 2+ state exhausts only a fraction of the total B(E2) strength, which is mainly collected in excited states around 5 MeV. This effect is sensitive to the energy splitting between the fp shell and the g_{9/2}orbital. We argue that the small experimental B(E2) value is not strong evidence for the double-magic character of 68Ni., 4 pages, 4 figures

In certain neutron-rich Te isotopes, a decrease in the energy of the first excited ${2}^{+}$ state is accompanied by a decrease in the $E2$ strength to that state from the ground state, contradicting simple systematics and general intuition about quadrupole collectivity. We use a separable quadrupole-plus-pairing Hamiltonian and the quasiparticle random phase approximation to calculate energies, ${B(E2,0}^{+}\ensuremath{\rightarrow}{2}^{+})$ strengths, and g factors for the lowest ${2}^{+}$ states near ${}^{132}\mathrm{Sn}$ $(Zg~50).$ We trace the anomalous behavior in the Te isotopes to a reduced neutron pairing above the $N=82$ magic gap.

We discuss the different contributions to the pairing interaction acting among nucleons moving in time-reversal states close to the Fermi energy and the consequences it may have on the transition taking place between superfluid and normal phases as a function of the rotational frequency and of temperature. Special emphasis is set on the induced interaction mediated by the exchange of vibrational modes.

The three-body description of two-neutron halo systems is extended to allow for core polarization taking into account the associated effects of mass-renormalization (single-particle motion) and induced interaction (density dependent pairing force) in terms of the particle-vibration coupling formalism. This formalism is applied to 10Li and 11Li. Theory reproduces most of the attractive features of Faddeev type calculations providing, in addition, an overall account of the experimental findings.

Recent theoretical advances in the large-scale HFBTHO calculations of nuclear ground-state properties are presented with the emphasis on the exact particle number projection. The applicability of the widely used Lipkin-Nogami procedure is discussed together with the analysis of the particle number projection after variation.

We present test calculations of the quasiparticle random-phase approximation with Skyrme and delta-pairing forces. We examine the convergence of solutions in the isoscalar 0+ channel as we increase the number of single-quasiparticle states, and the separation of spurious states from physical excited states in the isoscalar 1− channel. Our calculation is fully self-consistent as it neglects no component of the interaction. We focus on Sn isotopes near the two-neutron drip line.

The overlap of the excited states in quasiparticle random-phase approximation (QRPA) is calculated to simulate the overlap of the intermediate nuclear states of the double-$\ensuremath{\beta}$ decay. Our basic idea is to use the like-particle QRPA with the aid of the closure approximation and calculate the overlap as rigorously as possible by making use of the explicit equation of the QRPA ground state. The formulation is shown in detail, and the mathematical properties of the overlap matrix are investigated. Two test calculations are performed for relatively light nuclei with the Skyrme and volume $\ensuremath{\delta}$-pairing energy functionals. The validity of the truncations used in the calculation is examined and confirmed.

Thirty-three of 34 cultured human lymphoblastoid B cell lines have been shown to express four out of five polymorphic non-HLA specificities expressed by normal B lymphocytes. The specificities were detected by 32 alloantisera produced by absorption with pooled platelets to remove HLA activity and selected from over 400 pregnancy sera. One B group (B2) which was expressed by 23% of a panel of normal B lymphocytes was not found on any of the cultured lines tested. Four T cell lines tested and myeloid line (K562) did not react with any of the B cell alloantisera.

The possible associations of HLA-DR antigens and predisposition to recurrent HSV infections were studied in patients with recurrent HSV 1 and HSV 2 infections. HLA-DR antigens have been determined in over 34 patients with recurrent HSV stromal keratitis (HSV type 1). An increased frequency HLA-DRw3 was found in the patient group (35%) compared to the control group (23%) but the P value was not statistically significant HLA-DRw7 was also found with increased frequency in the patient group (38%) compared to the control group (22%). The uncorrected P value of