Massless versus massive Hawking radiation in AdS2 spacetime

We study massless and massive Hawking radiations on a two-dimensional AdS spacetime. For the massless case, the quantum stress-energy tensor of a massless scalar field on the AdS background is calculated, and the expected null radiation is obtained. However, for the massive case, the scattering analysis is performed in order to calculate the absorption and reflection coefficients which are related to statistical Hawking temperature. On the contrary to the massless case, we obtain a nonvanishing massive radiation.     

Quasinormal Modes of the Schwarzschild Black Hole Surrounded by the Quintessence Field in Rastall Gravity

The quasinormal modes of the Schwarzschild black hole surrounded by the quintessence in Rastall gravity are studied using the sixth-order Wentzel-Kramers-Brillouin approximative approach. The effect of the Rastall parameter on the quasinormal modes of gravitational, electromagnetic and massless scalar perturbations is explored. Compared to the case of Einstein gravity, it is found that, when η < 0, the gravitational field, electromagnetic field as well as massless scalar field damp more rapidly and have larger real frequency of oscillation in Rastall gravity, while when η > 0, the gravitational field, electromagnetic field as well as massless scalar field damp more slowly and have smaller real frequency of oscillation in Rastall gravity. It is also found that the gravitational field, electromagnetic field as well as massless scalar field damp more and more slowly and the real frequency of oscillation for the gravitational perturbation, electromagnetic perturbation as well as massless scalar perturbation becomes smaller and smaller as the Rastall parameter η increases. Compared among the quasinormal frequencies of gravitational, electromagnetic and massless scalar perturbations, I find that, for fixed η, (l, n), ∈ and N_q, the oscillation damps most slowly for the gravitational perturbation, mediate for the electromagnetic perturbation and most rapidly for the massless scalar perturbation, and the real frequency of oscillation is the smallest for the gravitational perturbation, mediate for the electromagnetic perturbation and the largest for the massless scalar perturbation in Rastall gravity.     

Non-commutative Geometry in Massless and Massive Particles

In this paper, we study the symmetries of massless and massive particles action. By considering the non-commutative space-time, we find appropriate non-commutative relation for relativistic particles which leaves invariant the non-commutative Minkowski space-time. We show that non-commutativity break the scale and conformal invariance in massless and massive action. So, in non-commutative space-time the massless and massive particles have same symmetry.     

Massless D-Branes on Calabi–Yau Threefolds and Monodromy

We analyze the link between the occurrence of massless B-type D-branes for specific values of moduli and monodromy around such points in the moduli space. This allows us to propose a classification of all massless B-type D-branes at any point in the moduli space of Calabi–Yau’s. This classification then justifies a previous conjecture due to Horja for the general form of monodromy. Our analysis is based on using monodromies around points in moduli space where a single D-brane becomes massless to generate monodromies around points where an infinite number become massless. We discuss the various possibilities within the classification.     

Inclusive D^* production in photon-photon collisions at next-to-leading order QCD}

The next-to-leading order cross section for the inclusive production of charm quarks in collisions is calculated as a function of the transverse momentum and the rapidity y in approaches using massive or massless charm quarks. For the direct cross section we derive the massless limit from the massive theory with the result that this limit differs from the massless version with factorization by finite corrections. Subtracting or adding these corrections allows us to compare the two approaches on equal footing. We establish massless and massive versions with 3 and 4 initial flavours which are shown to approach the massless approximations very fast with increasing . With these results we calculate the inclusive cross section in collisions using realistic evolved fragmentation functions with appropriate factorization scales and compare with recent data for from three LEP collaborations after single- and double-resolved contributions have been added. Received: 25 September 2001 / Published online: 5 November 2001     

Spontaneously broken spacetime symmetries and Goldstone's theorem

Goldstone's theorem states that there is a massless mode for each broken symmetry generator. It has been known for a long time that the naive generalization of this counting fails to give the correct number of massless modes for spontaneously broken spacetime symmetries. We explain how to get the right count of massless modes in the general case, and discuss examples involving spontaneously broken Poincaré and conformal invariance.     

Anomalies and the particle content of grand unified theories

For the largest class of grand unified models based on simple gauge groups, the presence of anomalies not only results in unrenormalizability, but in addition means that there are charged, massless fermions in the theory. Conversely, the absence of charged, massless particles in such models guarantees the absence of anomalies. For models outside this class, if there are anomalies but no charged massless fermions, the anomalies occur only for rather exotic currents.     

Renormalization group and infrared behaviour in theories with coupled massless fields

The renormalization-group method is applied to investigate the infrared singularities in gauge theories with Abelian or non-Abelian symmetry, involving both massive and massless fermions. In the Abelian gauge model the infrared structures of massive and massless fermion propagators and of a massive fermion form factor are found. In the non-Abelian gauge model (quantum chromodynamics) the infrared behaviour of a massless gluon propagator and a massive quark form factor is considered in the logarithmic approximation.     

Spin-1/2 and spin-3/2 field solutions in plane wave spacetimes

We have found two non-trivial massless Dirac and two massive Rarita–Schwinger solutions in plane wave spacetimes. The first order symmetry operator transforming one of the massless Dirac solution to the other is constructed. The only non-vanishing spinor bilinear generated by the standard spinor basis is obtained and algebraic relations between the induced parallel forms are demonstrated. It is also seen that the spin-3/2 norm of the Rarita–Schwinger solutions enforces to the massless sector.     

Massless spectrum and critical dimension of the supermembrane

We show the existence of massless particles in the supermembrane. These occur in the sector of a completely collapsed membrane and receive zero vacuum energy thanks to supersymmetry. Only in the 11-dimensional supermembrane the massless states include a graviton. Thus, in the critical dimension d = 11 the massless particles correspond to the supergravity multiplet. We also find that higher extended objects beyond the supermembrane have no critical dimension in which the supergravity multiplet emerges.     

Gravitational scattering of massless scalars in QFT and superstring theory

In this paper we perform the calculation of the gravitational scattering amplitude for 4 massless scalars in quantum field theory and Type II superstring theory. We show that the results agree, providing an example of how gravity is incorporated in the superstring theory. During the calculation we quantize gravitational action to derive graviton propagator and interaction vertex with massless scalar. We also calculate general 3‐point and 4‐point scattering amplitudes in SST for open and closed massless strings in NS sector.     

The Adler condition and high energy bounds on massless particle total cross sections

We study the problem of deriving high energy bounds on total cross sections for processes in which massless particles can participate. We are able to prove such bounds given the following assumptions 1) Mandelstam analyticity 2) polynomial boundedness 3) smoothness 4) Adler's condition for massless pions or analogous conditions for other massless particles such as neutrinos. The resulting bound is that total cross sections are constant up to powers of logarithims of the energy.     

Physical charged fermions in the fermion-monopole system

In order to demonstrate existence of physical charged fermions in the system consisting of a doublet of J = 0 massless fermions coupled to the radial electric field in the presence of a point-like SU(2) monopole, it is shown that the system is equivalent to that of a doublet of two-dimensional massless fermions carrying renormalized charges. As a consequence, it follows that charges are quantized if we confine ourselves to Fock space of the free massless fermion fields.     

Inclusive D production in $\gamma \gamma$ collisions: including the single-resolved contribution with massive quarks

We have calculated the next-to-leading order cross section for the inclusive production of charm quarks as a function of the transverse momentum p_T and the rapidity in two approaches using massive or massless charm quarks. For the single-resolved cross section we have derived the massless limit from the massive theory. We find that this limit differs from the genuine massless version with factorization by finite corrections. By adjusting subtraction terms we establish a massive theory with subtraction which approaches the massless theory very fast with increasing transverse momentum. With these results and including the equivalent results for the direct cross section obtained previously as well as double-resolved contributions, we calculate the inclusive cross section in collisions using realistic evolved non-perturbative fragmentation functions and compare with recent data from the LEP collaborations ALEPH, L3 and OPAL. We find good agreement. Received: 14 February 2003 / Published online: 5 May 2003     

Single Transverse Spin Asymmetries at Parton Level

Two factorization approaches have been proposed for single transverse spin asymmetries. One is the cofiinear factorization, the other is the transverse-momentum-dependent factorization. They have been previously derived in a formal way by using diagram expansion at hadron level. If the two factorizations hold or can be proven, they should also hold when we replace hadrons with patton states. We examine these two factorizations at patton level with massless partons. It is nontrivial to generate these asymmetries at parton level with massless patrons because the asymmetries require helicity-flip and nonzero absorptive parts in scattering amplitudes. By constructing suitable patton states with massless partons we derive the two factorizations for the asymmetry in Drell-Yan processes. It is found from our results that the collinear factorization derived at parton level is not the same as that derived at hadron level. Our results with massless partons confirm those derived with single massive parton state in our previous works.     

A note on the inverse scattering problem in quantum field theory

We study the set of local fields describing the dynamics of a scalar, massless particle. It turns out that these fields are relatively local to the free, massless, scalar fieldA if the massless particle does not interact. This leads to a simple algebraic characterisation of interacting fields in the above framework.     

Neutrino helicity flip in a curved space-time

In Minkowskian spaces, the helicity of a massless fermion is a conserved quantity. In principle, this property may not hold when gravitational effects are not neglected. In this context, this work proves that the helicity of a massless neutrino is not conserved in curved spaces. In order to show this fact, the time variation of the helicity in the Heisenberg picture is calculated. Also, we verify that the differential cross-section due to helicity flip of a massless neutrino in a curved space does not vanish as a result of the coupling between the spin and the curvature of space-time.     

Complex frequencies of a massless scalar field in loop quantum black hole spacetime

Recently,considerable progress has been made in understanding the early universe by loop quantum cosmology.Modesto et al.investigated the loop quantum black hole(LQBH)using improved semiclassical analysis and they found that the LQBH has two horizons,an event horizon and a Cauchy horizon,just like the Reissner-Nordstr¨om black hole.This paper focuses on the dynamical evolution of a massless scalar wave in the LQBH background.By investigating the relation between the complex frequencies of the massless scalar field and the LQBH parameters using the numerical method,we find that the polymeric parameter P makes the massless scalar field decay more quickly and makes the ground scalar wave oscillate slowly.However,the polymeric parameter P causes the frequency of the high harmonic massless scalar wave to shift according to its value.We also find that the loop quantum gravity area gap parameter a 0 causes the massless scalar field to decay more slowly and makes the period of the massless scalar field wave become longer.In the complex ω plane,the frequency curves move counterclockwise when the polymeric parameter P increases and this spiral effect is more obvious for a higher harmonic scalar wave.     

Four-dimensional heterotic strings and conformal field theory

The techniques of (super) conformal field theory are applied to 4-dimensional heterotic string theories. We discuss certain aspects of 4-dimensional strings in the framework of the bosonic lattice approach such as the realization of superconformal symmetry, character valued partition functions, construction of vertex operators and ghost picture changing. As an application we compute all possible 3- and 4-point tree amplitudes of the massless fields and derive from them the low energy effective action of the massless modes. Some effects for the massless spectrum due to one-loop string effects are also mentioned.