118565456
Stability of BTZ black strings
We study the dynamical stability of the Banados-Teitelboim-Zanelli (BTZ) black string against fermionic and gravitational perturbations. The BTZ black string is not always stable against these perturbations. There exist threshold values for m{sup 2} related to the compactification of the extra dimension for fermionic perturbation, the scalar part of the gravitational perturbation, and the tensor perturbation, respectively. Above the threshold values, perturbations are stable; while below these thresholds, perturbations can be unstable. We find that this nontrivial stability behavior qualitatively agrees with that predicted by a thermodynamical argument, showing that the BTZ black string phase is not the privileged stable phase.
122741264
Quantum cosmology at finite temperature in superstring theory
We study cosmology induced by an ideal superstring gas at finite temperature. The thermal/quantum effects of the string gas generate a nontrivial effective potential at one-loop level. At certain points in the moduli space where generically massive states become massless, the effective potential develops local minima. The latter serve as moduli attractors, which induce time-dependent scalar masses decreasing in cosmological time. As a result, the coherent scalar oscillations dilute before nucleosynthesis, and the cosmological moduli problem is avoided. In particular, we study moduli stabilization in the cases of cosmology induced by i) a maximally supersymmetric heterotic string gas; ii) a gas of type II string compactified on Calabi-Yau three-folds. In case i), the local minima of the potential arise at enhanced gauge symmetry points, which can stabilize all moduli but the dilaton. In case ii), local minima of the effective potential are reached at the loci where 2-spheres or 3-spheres in the Calabi-Yau space shrink to zero size, giving rise to either conifold transitions or non Abelian gauge symmetries. Extra massless states are induced by D-brane wrapping the shrinking spheres, and the stabilized moduli are those controlling the volume of those spheres. In addition, in the two cases we also study respectively the type I dual theory which is maximally supersymmetric and the heterotic dual theory compactified on K3xT2. We show that dual moduli can be stabilized by novel non-perturbative effects implied by duality maps.
54192043
Lecture notes on thermodynamics of ideal string gases and its application in cosmology
In these lecture notes I give a pedagogical introduction to the thermodynamics of ideal string gases. The computation of thermodynamic quantities in the canonical ensemble formalism will be shown in detail with explicit examples. Attention will be given mainly to the thermodynamical consequences of string degrees of freedom, where I will especially address i) the Hagedorn temperature, a critical temperature above which the canonical ensemble description breaks down, which can be the onset point of some instability of the string gas; ii) the phase structure arising from compactification, embodied in the moduli-dependence of the Helmholtz free energy, which corrects the tree-level vacuum and can provide mechanism for moduli stabilization. Then I will briefly explain the implementation of string gas thermodynamics in cosmology, showing a simple example which gives rise to a radiation-dominated early universe. Further phenomenological issues and open questions will be discussed qualitatively with references indicated, including the Hagedorn instability in the resolution of the initial singularity, moduli stabilization, generation of hierarchy, radiative symmetry breaking and primordial cosmological fluctuations.
119217520
Moduli stabilisation in early superstring cosmology
We study the cosmological evolution induced by the free energy of a string gas at finite temperature. We first consider the maximally supersymmetric heterotic string in the weak coupling regime in dimension D ≥ 4. The free energy develops local minima associated to some gauge symmetry enhancement induced by perturbative states. This can stabilize all heterotic moduli except the dilaton. By string-string S-dualities, it follows that the dual type I moduli can be stabilized by either non perturbative D-string states or perturbative open string states. We next consider the type II string compactified on Calabi-Yau three-folds, which has = 2 supersymmetry in D = 4. The moduli space has singular loci where the Calabi-Yau space undergoes extremal transitions, accompanied with either conifold transitions or certain gauge symmetry enhancement. Also the free energy reaches local minima due to the emergence of extra non perturbative massless modes. Consequently, the type II moduli are attracted to these singular loci. Using the type II/heterotic string duality, we can stabilize the dual heterotic moduli, and in particular it is possible to stabilize the heterotic dilaton.
118644408
Topological limit of gravity admitting an SU(2) connection formulation
We study the Hamiltonian formulation of the generally covariant theory defined by the Lagrangian 4-form L=e{sub I} and e{sub J} and F{sup IJ}({omega}), where e{sup I} is a tetrad field and F{sup IJ} is the curvature of a Lorentz connection {omega}{sup IJ}. This theory can be thought of as the limit of the Holst action for gravity for the Newton constant G{yields}{infinity} and Immirzi parameter {gamma}{yields}0, while keeping the product G{gamma} fixed. This theory has for a long time been conjectured to be topological. We prove this statement both in the covariant phase space formulation as well as in the standard Dirac formulation. In the time gauge, the unconstrained phase space of theory admits an SU(2) connection formulation which makes it isomorphic to the unconstrained phase space of gravity in terms of Ashtekar-Barbero variables. Among possible physical applications, we argue that the quantization of this topological theory might shed new light on the nature of the degrees of freedom that are responsible for black entropy in loop quantum gravity.
119186303
Moduli stabilization in type II Calabi-Yau compactifications at finite temperature
A bstractWe consider the type II superstring compactified on Calabi-Yau threefolds, at finite temperature. The latter is implemented at the string level by a free action on the Euclidean time circle. We show that all Kähler and complex structure moduli involved in the gauge theories geometrically engineered in the vicinity of singular loci are lifted by the stringy thermal effective potential. The analysis is based on the effective gauged super-gravity at low energy, without integrating out the non-perturbative BPS states becoming massless at the singular loci. The universal form of the action in the weak coupling regime and at low enough temperature is determined in two cases. Namely, the conifold locus, as well as a locus where the internal space develops a genus-g curve of AN −1 singularities, thus realizing an SU(N ) gauge theory coupled to g hypermultiplets in the adjoint. In general, we argue that the favored points of stabilization sit at the intersection of several such loci. As a result, the entire vector multiplet moduli space is expected to be lifted, together with hypermultiplet moduli. The scalars are dynamically stabilized during the cosmological evolution induced by the back-reaction of the thermal effective potential on the originally static background. When the universe expands and the temperature T drops, the scalars converge to minima, with damped oscillations. Moreover, they store an energy density that scales as T4, which never dominates over radiation. The reason for this is that the mass they acquire at one-loop is of order the temperature scale, which is time-dependent rather than constant. As an example, we analyze the type IIA compactification on a hy-persurface $$ \mathbb{P}_{{\left( {1,1,2,2,6} \right)}}^4 $$ [12], with Hodge numbers h11 = 2 and h12 = 128. In this case, both Kähler moduli are stabilized at a point, where the internal space develops a node and an enhanced SU(2) gauge theory coupled to 2 adjoint hypermultiplets. This shows that in the dual thermal heterotic picture on K3 × T2, the torus modulus and the axio-dilaton are stabilized, though in a strong coupling heterotic regime.
39191409
Charmonium spectroscopy from an anisotropic lattice study
We present a progress report on our study of the charmonium spectrum in full QCD on anisotropic lattices generated by the Hadron Spectrum Collaboration. We adopt a large basis of interpolating operators to extract the excited charmonium states using the variational method. A detailed spectrum of excited charmonium mesons in many J PC channels is obtained. Hybrid states with exotic and non-exotic quantum numbers are determined and preliminary results from a study of disconnected contributions to the hc are presented.
119254926
Scaling of the Higgs Self-coupling and bounds on the Extra Dimension
In this paper we study the one-loop evolution equation of the Higgs quartic coupling $\lambda$ in the minimal Universal Extra Dimension model, and find that there are certain bounds on the extra dimension due to the singularity and vacuum stability conditions of the Higgs sector. In the range $250GeV \sim {R^{- 1}} \sim 80TeV$ of the compactification radius, we notice that for a given initial value $\lambda ({M_Z})$, there is an upper limit on ${R^{- 1}}$ for a Higgs mass of $183GeV \sim {m_H}({M_Z}) \sim 187GeV$; where any other compactification scales beyond that have been ruled out for theories where the evolution of $\lambda$ does not develop a Landau pole and become divergent in the whole range (that is, from the electroweak scale to the unification scale). Likewise, in the range of the Higgs mass $152GeV \sim {m_H}({M_Z}) \sim 157GeV$, for an initial value $\lambda ({M_Z})$, we are led to a lower limit on ${R^{- 1}}$; any other compactification scales below that will be ruled out for theories where the evolution of $\lambda$ does not become negative and destabilize the vacuum between the electroweak scale and the unification scale. For a Higgs mass in the range $157GeV < {m_H}({M_Z}) < 183GeV$, the evolution of $\lambda$ is finite and the theory is valid in the whole range (from the electroweak scale to the unification scale) for $250GeV \sim {R^{- 1}} \sim 80TeV$.
119090662
Sommerfeld's quantum condition of action and the spectra of Schwarzschild black hole
If the situation of quantum gravity nowadays is nearly the same as that of the quantum mechanics in it's early time of Bohr and Sommerfeld, then a first step study of the quantum gravity from Sommerfeld's quantum condition of action might be helpful. In this short paper the spectra of Schwarzschild black hole(SBH) in quasi-classical approach of quantum mechanics is given. We find the quantum of area, the quantum of entropy and the Hawking evaporation will cease as the black hole reaches its ground state.
8230888
Measurement of the cross section for electromagnetic dissociation with neutron emission in Pb-Pb collisions at sqrt[s(NN)] = 2.76 TeV.
The first measurement of neutron emission in electromagnetic dissociation of ^{208}Pb nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at sqrt[s(NN)]=2.76 TeV with neutron emission are σ(singleEMD)=187.4 ± 0.2(stat)(-11.2)(+13.2) (syst) b and σ(mutualEMD) = 5.7 ± 0.1(stat) ± 0.4(syst) b, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model.
121055509
The quantum cosmology in the Brans-Dicke theory
In this paper, we try to establish the quantum cosmology based on the Brans-Dicke gravitational theory. The most remarkable property of it is that the scale factora(t) has a lower limit, where the cosmological wave function approaches zero.