18121181
Geometric cross sections of rotating strings and black holes
We study the production cross section of a highly excited string with fixed angular momentum from an ultrahigh energy collision of two light strings. We find that the cross section exhibits geometric behavior in a certain region of angular-momentum/impact-parameter space. This geometric behavior is common to the differential cross sections of a black hole production with fixed angular momentum and thus we see another correspondence between strings and black holes.
7041909
Improved Taylor Expansion Method in the Ising Model
We apply an improved Taylor expansion method, which is a variational scheme to the Ising model in two dimensions. This method enables us to evaluate the free energy and magnetization in strong coupling regions from the weak coupling expansion, even in the case of a phase transition. We determine the approximate value of the transition point using this scheme. In the presence of an external magnetic field, we find both stable and metastable physical states.
119512374
Mean field approximation of IIB matrix model and emergence of four-dimensional space–time
Abstract For the purpose of analyzing non-perturbative dynamics of string theory, Nishimura and Sugino have applied an improved mean field approximation (IMFA) to IIB matrix model. We have extracted the essence of the IMFA and obtained a general scheme, the improved Taylor expansion, that can be applied to a wide class of series which is not necessarily convergent. This approximation scheme with the help of the 2PI free energy enables us to perform higher order calculations. We have shown that the value of the free energy is stable at higher orders, which supports the validity of the approximation. Moreover, the ratio between the extent of “our” space–time and that of the internal space is found to increase rapidly as we take the higher orders into account. Our results suggest that the four-dimensional space–time emerges spontaneously in IIB matrix model.
9129268
Drag force in SYM plasma with B field from AdS/CFT
We investigate drag force in a thermal plasma of N=4 super Yang-Mills theory via both fundamental and Dirichlet strings under the influence of non-zero NSNS B-field background. In the description of AdS/CFT correspondence the endpoint of these strings correspondes to an external monopole or quark moving with a constant electromagnetic field. We demonstrate how the configuration of string tail as well as the drag force obtains corrections in this background.
118461510
Emission spectrum of soft massless states from heavy superstring
We calculate emission rates of various bosonic/fermionic soft massless states of an open/closed superstring from an ensemble of a highly excited open/closed superstring in the flat background. The resulting spectrum shows thermal distributions at the Hagedorn temperature. We find greybody factors for each process and observe their relation to the ones from black holes.
14895195
STRING CREATION IN D6-BRANE BACKGROUND
The production of string charge during a crossing of certain oriented D-branes is studied. We compute the string charge in the system of a probe D2-brane and a background D6-brane by using the equations of motion in ten dimensions. We confirm the creation of string charge as inflow from the background D6-brane.
9741554
CCD Photometry of a Newly Confirmed SU UMa-Type Dwarf Nova, NSV 4838
We present time-resolved CCD photometry of a dwarf nova, NSV 4838 (UMa 8, SDSS J102320.27+440509.8), during 2005 June and 2007 February outbursts. The two light curves showed superhumps with mean periods of 0.0699(1) d for the 2005 outburst and 0.069824(83) d for the 2007 outburst. Using its known orbital period of 0.0678 d, we estimated the mass ratio of the system to be q = 0.13 based on an empirical relation. Although the majority of SU UMa-type dwarf novae having similar superhump periods show negative period derivatives, we found that the superhump period increased at P P= Psh =+ 7(+3, � 4) � 10 � 5 during the 2007 superoutburst. We also