119289762
Quantum gravity effects on compact star cores
Abstract Using the Tolman–Oppenheimer–Volkoff equation and the equation of state of zero temperature ultra-relativistic Fermi gas based on generalized uncertainty principle (GUP), the quantum gravitational effects on the cores of compact stars are discussed. Our results show that 2 m ( r ) / r varies with r. Quantum gravity plays an important role in the region r ∼ 10 3 r 0 , where r 0 ∼ β 0 l p , l p is the Planck length and β 0 is a dimensionless parameter accounting for quantum gravity effects. Furthermore, near the center of compact stars, we find that the metric components are g t t ∼ r 4 and g r r = [ 1 − r 2 / ( 6 r 0 2 ) ] − 1 . All these effects are different from those obtained from classical gravity. These results can be applied to neutron stars or denser ones like quark stars. The observed masses of neutron stars ( ⩽ 2 M ⊙ ) indicate that β 0 can not exceed 1037, not as good as the upper bound β 0 10 34 from simple electroweak consideration. This means that incorporating either quantum gravity effects or nuclear interactions, one obtains almost the same mass limits of neutron stars.
119256430
Remnants, fermions’ tunnelling and effects of quantum gravity
A bstractThe remnants are investigated by fermions’ tunnelling from a 4-dimensional charged dilatonic black hole and a 5-dimensional black string. Based on the generalized uncertainty principle, effects of quantum gravity are taken into account. The quantum numbers of the emitted fermions affects the Hawking temperatures. For the black hole, the quantum gravity correction slows down the increase of the temperature, which leads to the remnant left in the evaporation. For the black string, the existence of the remnant is determined by the quantum gravity correction and effects of the extra compact dimension.
123394838
Calculation of the one point Green's function for a g phi 4 quantum field theory
119746683
Generalized Uncertainty Principle in the Presence of Extra Dimensions
We argue that in the generalized uncertainty principle (GUP) model, the parameter ?0 whose square root, multiplied by Planck length ?p, approximates the minimum measurable distance, varies with energy scales. Since the minimal measurable length and extra dimensions are both suggested by quantum gravity theories, we investigate the models based on the GUP and one extra dimension, compactified with radius ?. We obtain an inspiring relation . This relation is also consistent with the predictions at Planck scale and the usual quantum mechanics scale. We also estimate the application range of the GUP model. It turns out that the minimum measurable length is exactly the compactification radius of the extra dimension.
17081750
String Field Theory and Tachyon Dynamics
In this thesis we present some works done during my doctoral studies. These results focus on two directions. The first one is motivated by tachyon dynamics in open string theory. We calculate the stress tensors for the p-adic string model and for the pure tachyonic sector of open string field theory (OSFT). We give the energy density of lump solutions and attempt to evaluate the evolution of the pressure in rolling tachyon solutions. We discuss the relevance of the pressure calculation for the identification of the large time solution with a gas of closed strings. In the second direction, we give some results in closed string field theory (CSFT). We considered marginal deformations in CSFT. The marginal parameter, called a, is that associated with the dimension-zero primary operator cWcX&X. We use this marginal operator to test the quartic structure of CSFT and the feasibility of level expansion. We check the vanishing of the effective potential for a. In the level expansion the quartic terms generated by the cubic interactions must be cancelled by the elementary quartic interaction of four marginal operators. We confirm this prediction, thus giving evidence that the sign, normalization, and region of integration Vo, 4 for the quartic vertex are all correct. This is the first calculation of an elementary quartic amplitude for which there is an expectation that can be checked. We also extend the calculation to the case of the four marginal operators associated with two space coordinates. We then try to search a critical point of the tachyon potential in CSFT. We include the tachyon, the dilaton, and massive fields in the computation. Some evidence is found for the existence of a closed string tachyon vacuum. It seems that this critical point becomes more shallow when higher level contributions are considered. We also relate fields in the sigma model and those in CSFT. Moreover, large dilaton deformations are studied numerically. Finally, we use the low-energy effective field equations that couple gravity, the dilaton, and the bulk closed string tachyon to study the end result of the physical decay process associated with the instability of closed string tachyon. We establish that whenever the tachyon induces the rolling process, the Einstein metric undergoes collapse while the dilaton rolls to strong coupling. Some more general potentials and the possible cosmological application are discussed. Thesis Supervisor: Barton Zwiebach Title: Professor of Physics
119468158
The nonperturbative closed string tachyon vacuum to high level
We compute the action of closed bosonic string field theory at quartic order with fields up to level ten. After level four, the value of the potential at the minimum starts oscillating around a nonzero negative value, in contrast with the proposition made in [5]. We try a different truncation scheme in which the value of the potential converges faster with the level. By extrapolating these values, we are able to give a rather precise value for the depth of the potential.
15090356
Dark Energy and Emergent Spacetime
A natural geometric framework of noncommutative spacetime is symplectic geometry rather than Riemannian geometry. The Darboux theorem in symplectic geometry then admits a novel form of the equivalence principle such that the electromagnetism in noncommutative spacetime can be regarded as a theory of gravity. Remarkably the emergent gravity reveals a noble picture about the origin of spacetime, dubbed as emergent spacetime, which is radically different from any previous physical theory all of which describe what happens in a given spacetime. In particular, the emergent gravity naturally explains the dynamical origin of flat spacetime, which is absent in Einstein gravity: A flat spacetime is not free gratis but a result of Planck energy condensation in a vacuum. This emergent spacetime picture, if it is correct anyway, turns out to be essential to resolve the cosmological constant problem, to understand the nature of dark energy and to explain why gravity is so weak compared to other forces.
16109424
Frequency scanned interferometry for ILC tracker alignment
In this paper, we report high-precision absolute distance and vibration measurements performed with frequency scanned interferometry using a pair of single-mode optical b ers. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. A high-nesse Fabry-Perot interferometer was used to determine frequency changes during scanning. A dual-laser scanning technique was used to cancel drift errors to improve the absolute distance measurement presicion. Under realistic conditions, a precision of 0.16 microns was achieved for absolute distance of 0.41 meters. Numerical simulation of an optical alignment system for a single silicon ladder, cylinder is also presented. The motivation for this project is to design a novel optical system for quasi-real time alignment of tracker detector elements used in High Energy Physics (HEP) experiments. A.F. Fox-Murphy et.al. from Oxford University reported their design of a frequency scanned interferometer (FSI) for precise alignment of the ATLAS Inner Detector [1, 2]. Given the demonstrated need for improvements in detector performance, we plan to design and prototype an enhanced FSI system to be used for the alignment of tracker elements in the next generation of electron-positron Linear Collider detectors. Current plans for future detectors require a spatial resolution for signals from a tracker detector, such as a silicon microstrip or silicon drift detector, to be approximately 7-10 m [3]. To achieve this required spatial resolution, the measurement precision of absolute distance changes of tracker elements in one dimension should be on the order of 1 m . Simultaneous measurements from hundreds of interferometers will be used to determine the 3-dimensional positions of the tracker elements. The University of Michigan group has constructed several demonstration Frequency Scanned Interferometer (FSI) systems with the laser light transported by air or single-mode optical b er, using single-b er and dual-laser scanning techniques for initial feasibility studies. Absolute distance was determined by counting the interference fringes produced while scanning the laser frequency. The main goal of the demonstration systems was to determine the potential accuracy of absolute distance measurements that could be achieved under both controlled and realistic conditions. Secondary goals included estimating the eects of vibrations and studying error sources crucial to the absolute distance accuracy. Two multiple-distance-measurement analysis techniques were developed to improve distance precision and to extract the amplitude and frequency of vibrations. Under laboratory conditions, a measurement precision of 50 nm was achieved for absolute distances ranging from 0.1 meters to 0.7 meters by using the rst multipledistance-measurement technique. The second analysis technique has the capability to measure vibration frequencies ranging from 0.1 Hz to 100 Hz with amplitude as small as a few nanometers, without a priori knowledge[4]. The multiple-distance-measurement analysis techniques are well suited for reducing vibration eects and uncertainties from fringe & frequency determination, but do not handle well the drift errors such as from thermal eects. In this paper, we describe a dual-laser system intended to reduce the drift errors and show some results under realistic conditions. Numerical simulation of an optical alignment system for a single silicon ladder and for cylinders is also presented.
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.
18986664
Discovery Potential of the Standard Model Higgs Boson Through H -> WW Decay Mode with the ATLAS Detector at LHC
We report results of a study of the Standard Model Higgs boson discovery potential through the W-pair leptonic decay modes with the ATLAS detector at LHC at 14 TeV center-of-mass energy. We used MC samples with full detector simulation and reconstruction of the ATLAS experiment to estimate the ATLAS detection sensitivity for the reaction of pp -> H -> WW -> e\nu \mu\nu with no hard jet or two hard jets in the final states. The prospects for the Higgs boson searches at ATLAS are presented, including trigger efficiencies and data-driven methods to estimate the backgrounds using control samples in data. With 10/fb of integrated luminosity, one would expect to discover a Standard Model Higgs boson with ATLAS detector in Higgs boson mass range 135 < m_H < 190 GeV. If the Higgs boson does not exist, we will extend and confirm the exclusion produced by the Tevatron Higgs boson search result, which has ruled out the Higgs boson mass range of 160 < m_H < 170 GeV at 95% confidence level. If Higgs boson would be discovered, ATLAS could measure its mass with a precision of about 2 and 7 GeV for Higgs boson mass around 160 GeV and 130 GeV, respectively.
16912746
Towards an Efficient Prototype of a RPC Detector Readout System for the Daya Bay Neutrino Experiment
The Daya Bay RPC (Resistive Plate Chamber) readout system is responsible for collecting event data created by muons entering the detector systems from above. The readout system should be capable of converting analog signals from the RPC detectors into digital signals, which are buffered and uploaded for readout by the online DAQ (Data Acquisition) system. The RPC readout system will report trigger information to a master trigger system. The numerous and relatively minute pulses from the RPC detectors require accurate signal discriminating and reliable data transmission. This article provides a brief overview of the Daya Bay RPC detector and then outlines the design and performance of the prototype RPC readout system.