17895994
TASI Lectures on Perturbative String Theories
These lecture notes are based on a course on string theories given by Hirosi Ooguri in the first week of TASI 96 Summer School at Boulder, Colorado. It is an introductory course designed to provide students with minimum knowledge before they attend more advanced courses on non-perturbative aspects of string theories in the School. The course consists of five lectures: 1. Bosonic String, 2. Toroidal Compactifications, 3. Superstrings, 4. Heterotic Strings, and 5. Orbifold Compactifications.
17461222
The principle of least action and the geometric basis of D-branes
We analyze thoroughly the boundary conditions allowed in classical non-linear sigma models and derive from first principle the corresponding geometric objects, i.e. D-branes. In addition to giving classical D-branes an intrinsic and geometric foundation, D-branes in nontrivial H flux and D-branes embedded within D-branes are precisely defined. A well known topological condition on D-branes is replaced.
43434280
Matrix Description of Intersecting M5 Branes
Novel 3+1 dimensional N = 2 superconformal field theories (with tensionless BPS string solitons) are believed to arise when two sets of M5 branes intersect over a 3+1 dimensional hyperplane. We derive a DLCQ description of these theories as supersymmetric quantum mechanics on the Higgs branch of suitable 4d N = 1 supersymmetric gauge theories. Our formulation allows us to determine the scaling dimensions of certain chiral primary operators in the conformal field theories. We also discuss general criteria for quantum mechanical DLCQ descriptions of supersymmetric field theories (and the resulting multiplicities and scaling dimensions of chiral primary operators).
15577760
From boundaries to conditions over superspace
N = 1 and 2 superconformal boundary conditions are shown to be the consequence of a ``boundary'' on the worldsheet superspace with positive codimension in the anticommuting subspace. In addition to the well-known boundary conditions, I also find two new infinite series of N = 2 boundary states. Their free field realizations are given. A self-contained development of 2d superspace leads to new perspectives on this subject.
10041169
Conformal invariance on orbifolds and excitations of singularity
We study conformal field theory on two-dimensional orbifolds and show this to be an effective way to analyze physical effects of geometric singularities with angular deficits. They are closely related to boundaries and cross caps. Representative classes of singularities can be described exactly using generalizations of boundary states. From this we compute correlation functions and derive the spectra of excitations localized at the singularities.
5633727
Anomalies, Branes, and Currents
Abstract When a D-brane wraps around a cycle of a curved manifold, the twisting of its normal bundle can induce chiral asymmetry in its world-volume theory. We obtain the general form of the resulting anomalies for D-branes and their intersections. They are not cancelled among themselves, and the standard inflow mechanism does not apply at first sight because of their apparent lack of factorizability and the apparent vanishing of the corresponding inflow. We show, however, that after taking into consideration the effects of the non-trivial topology of the normal bundles, the anomalies can be transformed into factorized forms and precisely cancelled by finite inflow from the Chern-Simons actions for the D-branes as long as the latter are well defined. We then consider examples in type 11 compactifications where the twisting of the normal bundles occurs and calculate the changes in the induced Ramond-Ramond charges on the D-branes.
121970317
Charged particle identification with PHOS and central tracking of ALICE
The ALICE Photon Spectrometer (PHOS) has been designed to measure the photon spectrum produced in pp and AA collisions at LHC over a broad transverse momentum range from 0.5–100 GeV/c. We present a study on the matching of charged tracks, detected by the ALICE central tracking detectors, with clusters of hit PHOS elements. Matching efficiency and contamination due to false matches have been deduced for charged pions, muons and electrons. The study indicates also that material from other detectors in front of PHOS disturbs the photon detection.
108585326
Trigger electronics for the Alice PHOS detector
Abstract The Photon Spectrometer of ALICE consists of 5 identical modules of 56×64 PWO crystals with a total of 100° azimuthal coverage of the barrel. The electronics required for implementing both the L0 trigger for high luminosity p–p physics and the L1 trigger for high p T Pb+Pb physics has been studied. A full integration of the trigger logic into the detector's enclosure is based on analog transmission of fast trigger sums between stacks of front-end boards and trigger-router units. The latter contain 112 digitizer channels of 10 bit, which are mapped into a single FPGA per trigger unit, covering areas of 24×16 crystals. The running modes allow for Level-0 trigger at 800 ns and Level-1 at 6200 ns trigger latencies. The design and status of the PHOS trigger electronics are outlined.
110904443
Configurable electronics with low noise and 14-bit dynamic range for photodiode-based photon detectors
Abstract We describe the principles and measured performance of custom configurable 32-channel shaper/digitizer Front End Electronics (FEE) cards with 14-bit dynamic range for gain-adjustable photon detectors. The electronics has been designed for the PHOS calorimeter of ALICE with avalanche photodiode (APD) readout operated at −25 °C ambient temperature and a signal shaping time of 1 μs. The electronics has also been adopted by the EMCal detector of ALICE with the same APD readout, but operated at an ambient temperature of +20 °C and with a shaping time of 100 ns. The CR-RC2 signal shapers on the FEE cards are implemented in discrete logic on a 10-layer board with two shaper sections for each input channel. The two shaper sections with gain ratio of 16:1 are digitized by 10-bit ADCs and provide an effective dynamic range of 14 bits. Gain adjustment for each individual APD is available through 32 bias voltage control registers of 10-bit range. The fixed gains and shaping times of the pole-zero compensated shapers are defined prior to FEE production by the values of a few R and C components. For trigger purposes, “fast OR” outputs with 12-bit dynamic range are available. FPGA based slave logic, combined with a USB processor supports a variety of remote control and monitoring features, including APD gain calibration. The measurements presented here for APDs at −25 °C ambient temperature and 1 μs shaping time achieve an average RMS noise level of 0.25 ADC counts or 290 electrons.The linearity over the dynamic range is better than 1%, as is the uniformity of shaping time and gain over 32 channels. Due to the excellent correspondence of the output pulse shape with offline fit, a differential timing resolution of less than 1.5 ns between channels has been achieved at ca. 2 GeV, i.e. at 1.5% of the dynamic range of PHOS.
118604753
Strange and multi-strange particle production in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV with ALICE
We present ALICE results on strange and multi-strange hadron production as a function of centrality in Pb-Pb collisions at $\sqrt{s_{{\rm NN}}} = 2.76~{\rm TeV}$ at the LHC. Their transverse momentum spectra, yields and particle ratios are compared to the corresponding measurements in pp collisions to address strangeness enhancement and high pT particle suppression. The results are also compared to measurements at RHIC and SPS energies.
122716775
Elliptic flow of strange and multi-strange particles in Pb-Pb collisions at $\sqrt{s_{NN}}$ = 2.76-TeV measured with ALICE