119236650
Emergent gravity and the cosmological constant problem
We address issues on the origin of gravity and the cosmological constant problem based on a recent understanding about the correspondence between noncommutative field theory and gravity. We suggest that the cosmological constant problem can be resolved in a natural way if gravity emerges from a gauge theory in noncommutative spacetime. Especially, we elucidate why the emergent gravity implies that vacuum energy does not gravitate but only fluctuations around the vacuum generate gravity. That is, a flat spacetime emerges from uniform condensation of energy, previously identified with the cosmological constant.
18014891
Twisted bundles on noncommutative T4 and D-brane bound states
We construct twisted quantum bundles and adjoint sections on noncommutative $T^4$, and investigate relevant D-brane bound states with non-Abelian backgrounds. We also show that the noncommutative $T^4$ with non-Abelian backgrounds exhibits SO$(4,4|Z)$ duality and via this duality we get a Morita equivalent $T^4$ on which only D0-branes exist. For a reducible non-Abelian background, the moduli space of D-brane bound states in Type II string theory takes the form $\prod_a (T^4)^{q_a}/S_{q_a}$.
15769713
A Complete Classification of D-branes in Type IIB Plane Wave Background
We give a complete classification of D-branes in the type IIB plane wave background using Green-Schwarz superstring theory. We find all possible supersymmetric oblique and curved D-branes and consider their intersections. The supersymmetries preserved by various configurations of these D-branes are also identified. In particular, we show that D+-branes of type (+,−, n, n) for n = 1, 2, 3, 4 preserve 4 dynamical supersymmetries by introducing gauge field excitations and newly discovered oblique D5and D7-branes also preserve four or two dynamical supersymmetries with gauge field condensates. Furthermore we find new curved D-branes preserving four dynamical supersymmetries.
118961522
Comments on Instantons on Noncommutative R 4
We study U(1) and U(2) instanton solutions on noncommutative R 4 based on the noncommutative version of ADHM equation proposed by Nekrasov and Schwarz. It is shown that the anti-self-dual gauge fields on self-dual noncommutative R 4 correctly give integer instanton numbers for all cases we consider. We also show that the completeness relation in the ADHM construction is generally satisfied even for noncommutative spaces.
119204681
Emergent Spacetime and The Cosmological Constant
We address issues on the origin of gravity and the dark energy (or the cosmological constant) from the perspectives of emergent gravity. We discuss how the emergent gravity reveals a noble, radically different picture about the origin of spacetime, which is crucial for a tenable solution of the cosmological constant problem. In particular, the emergent gravity naturally explains the dynamical origin of flat spacetime, which is absent in Einstein gravity.
12060341
ALE spaces from noncommutative U(1) instantons via exact Seiberg-Witten map
The exact Seiberg–Witten (SW) map of a noncommutative (NC) gauge theory gives the commutative equivalent as an ordinary gauge theory coupled to a field dependent effective metric. We study instanton solutions of this commutative equivalent whose self-duality equation turns out to be the exact SW map of NC instantons. We derive general differential equations governing U(1) instantons and we explicitly get an exact solution corresponding to the single NC instanton. Remarkably the effective metric induced by the single U(1) instanton is related to the Eguchi–Hanson metric—the simplest gravitational instanton. Surprisingly the instanton number is not quantized but depends on an integration constant. Our result confirms the expected non-perturbative breakdown of the SW map. However, the breakdown of the map arises in a consistent way: the instanton number plays the role of a parameter giving rise to a one-parameter family of Eguchi–Hanson metrics.
16647938
Searches for Gauge-Mediated SUSY Breaking Topologies with the L3 Detector at LEP
Searches for topologies predicted by gauge‐mediated SUSY breaking models were performed using data collected with the L3 detector at LEP. All possible lifetimes of the next‐to‐lightest SUSY particle (NLSP), neutralino or scalar tau, were considered. No evidence for these new phenomena was found and limits on the production cross sections and sparticle masses were derived. A scan over the parameters of the minimal GMSB model was performed, leading to lower limits of 62.2 GeV, 11 TeV, and 0.07 eV on the NLSP mass, the mass scale parameter Λ, and the gravitino mass, respectively. The status of the LEP combined searches is also discussed.
119200112
Double field theory inspired cosmology
Double field theory proposes a generalized spacetime action possessing manifest T-duality on the level of component fields. We calculate the cosmological solutions of double field theory with vanishing Kalb-Ramond field. It turns out that double field theory provides a more consistent way to construct cosmological solutions than the standard string cosmology. We construct solutions for vanishing and non-vanishing symmetry preserving dilaton potentials. The solutions assemble the pre- and post-big bang evolutions in one single line element. Our results show a smooth evolution from an anisotropic early stage to an isotropic phase without any special initial conditions in contrast to previous models. In addition, we demonstrate that the contraction of the dual space automatically leads to both an inflation phase and a decelerated expansion of the ordinary space during different evolution stages.
18270173
Identified particle production in p + p and d +Au collisions at RHIC
The BRAHMS experiment at RHIC has measured the transverse momentum spectra of charged pions, kaons and (anti-)protons over a wide range of rapidity in d+Au and p+p collisions at √SNN = 200 GeV. The nuclear modification factor R dAu at forward rapidity shows a clear suppression for π + . The measured net-proton yields in p+p collisions are compared to PYTHIA and HIJING/B and seem to be better described by the latter.
17682877
Impact of Tracker Design on Higgs and Slepton Measurements
We have studied the impact of charged track resolution on Higgs mass and production cross section measurement in the process e+e− → Z0H,Z0 → + −,H → X for Higgs masses between 120 and 160 GeV, and on smuon mass measurement using smuon pair production for three different mass pairs, assuming the International Linear Collider(ILC) is operated at 500 GeV center of mass energies (CME) with integrated luminosities of 500 fb−1. The effect of initial state radiation (ISR), beamstrahlung and beam energy spread on Higgs and smuon mass measurement are also estimated. Using fast Monte Carlo simulations of the 2001 North American baseline detector designs (LD and SD), we find that the ISR and beamstrahlung have significant impact on Higgs and smuon mass measurement; Charged track momentum resolution affect Higgs mass significantly with better track performance yielding better Higgs mass resolution and precision for the track momentum resolution improvement up to a factor of about 5; Track momentum resolution has little effect on the measurement precision of the Higgsstrahlung cross section, the branching ratio of H → CC, the smuon and neutralino masses; Beam energy spread better than about 0.2% has little effect on Higgs, smuon and neutralino masses; The SD detector provides a more accurate measurement than the LD of the Higgs mass.
15273018
Testing closed string field theory with marginal fields
We study the feasibility of level expansion and test the quartic vertex of closed string field theory by checking the flatness of the potential in marginal directions. The tests, which work out correctly, require the cancellation of two contributions: one from an infinite-level computation with the cubic vertex and the other from a finite-level computation with the quartic vertex. The numerical results suggest that the quartic vertex contributions are comparable or smaller than those of level four fields.