Searching singlet extensions of the supersymmetric standard model in Z 6−II orbifold compactification of heterotic string

We search for supersymmetric standard model realizations with extra singlets and extra U(1) using the heterotic string compactification on the Z _6?II orbifold with two Wilson lines. The effective superpotential produced through the vacuum restabilization mechanism is examined for three representative Pati–Salam string models obtained in the literature. An automated selection of semi-realistic vacua along flat directions in the non-Abelian singlet modes field space is performed by requiring the presence of massless pairs of electroweak Higgs bosons having trilinear superpotential couplings with massless singlet modes and the decoupling of color triplet exotic modes needed to suppress B and L number violating processes.     

Behavior of boundary string field theory associated with integrable massless flow

We put forward an idea that the boundary entropy associated with integrable massless flow of thermodynamic Bethe ansatz (TBA) is identified with tachyon action of boundary string field theory. We show that the temperature parametrizing a massless flow in the TBA formalism can be identified with tachyon energy for the classical action at least near the ultraviolet fixed point, i.e., the open string vacuum.     

Superconductivity in Restricted Chromo-Dynamics (RCD) in SU(2) and SU(3) Gauge Theories

Characterizing the dyonically condensed vacuum by the presence of two massive modes (one determining how fast the perturbative vacuum around a colour source reaches the condensation and the other giving the penetration length of colored flux) in SU(2) theory, it has been shown that due to the dynamical breaking of magnetic symmetry the vacuum of RCD acquires the properties similar to those of relativistic superconductor. Analysing the behaviour of dyons around RCD string, the solutions of classical field equations have been obtained and it has been shown that magnetic constituent of dyonic current is zero at centre of the string and also at the points far away from the string. Extending RCD in the realistic color gauge group SU(3), it has been shown that the resulting Lagrangian leads to dyonic condensation, color confinement and the superconductivity with the presence of two scalar modes and two vector modes.     

Phenomenology and conformal field theory or can string theory predict the weak mixing angle?

We show that the weak mixing angle θ_w is the same for continuously connected classical vacua of the heterotic string which have chiral fermions in their massless spectra. We also show that the world-sheet quantum field theory for any classical vacuum with spacetime supersymmetry possesses an N = 2 superconformal invariance.     

Modifying the bosonic string vacuum

A nontrivial string vacuum can induce effects in open bosonic string theories which can be interpreted in terms of nonlocality of the mapping of the string world sheet into spacetime. This is achieved by modifying the sum over Riemann surfaces to include boundaries on which the bosonic fields satisfy a Dirichlet condition, as well as holes with the usual Neumann condition and crosscaps. Such effects profoundly alter the large-angle behaviour of string amplitudes. With suitable normalization, they also lead to a cancellation of the one-loop divergence associated with the vacuum emission of a soft dilaton.     

Bound-states of D-branes in L–R asymmetric superstring vacua

We discuss bound-states of D-branes in truly L–R asymmetric and thus non-geometric Type II vacuum configurations with extended supersymmetry. We argue for their stability as a result of residual supersymmetry and coupling to R–R potentials surviving in the massless spectrum. We then identify the open string excitations of these L–R asymmetric BPS D-branes. Finally, we briefly comment on possible applications and extensions.     

σ-model β-functions and ghost-free string effective actions

We explore the relationship between the effective action for a bosonic string propagating in a massless background and the corresponding σ-model, and show that a simple criterion proposed by Mavromatos and Miramontes leads to a manifestly ghost-free form for the O(α'²) action     

Small E8 instantons and tensionless non-critical strings

T-duality is used to extract information on an instanton of zero size in the E₈ × E₈ heterotic string. We discuss the possibility of the appearance of a tensionless anti-self-dual non-critical string through an implementation of the mechanism suggested by Strominger of two coincident 5-branes. It is argued that when an instanton shrinks to zero size a tensionless non-critical string appears at the core of the instanton. It is further conjectured that the appearance of tensionless strings in the spectrum leads to new phase transitions in six dimensions in much the same way as massless particles do in four dimensions.     

Vacuum instability of massless electrodynamics and the Gell-Mann-Low eigenvalue condition for the bare coupling constant

We discuss a connection of the Gell-Mann-Low eigenvalue condition for the bare coupling α₀ with the normal phase vacuum rearrangement in massless electrodynamics which results in the fermion acquiring a physical mass. A new approach to determine the Gell-Mann-Low eigenvalue for α₀ is proposed.     

Quantum dynamics of a massless relativistic string (II)

The massless relativistic free string is studied in the gauge x₀ = τ. It is found that the classical solutions include transverse and longitudinal vibrations. The problem is treated both in the Lagrangian and Hamiltonian formalism. Different ways of quantizing the system are investigated. The path integral quantization leads to a Poincaré invariant quantum theory in any number of dimensions.     

Tadpole resummations in string theory

While R–R tadpoles should be canceled for consistency, string models with broken supersymmetry generally have uncanceled NS–NS tadpoles. Their presence signals that the background does not solve the field equations, so that these models are in “wrong” vacua. In this Letter we investigate, with reference to some prototype examples, whether the true values of physical quantities can be recovered resumming the NS–NS tadpoles, hence by an approach that is related to the analysis based on String Field Theory by open–closed duality. We show that, indeed, the positive classical vacuum energy of a Dp-brane of the bosonic string is exactly canceled by the negative contribution arising from tree-level tadpole resummation, in complete agreement with Sen's conjecture on open-string tachyon condensation and with the consequent analysis based on String Field Theory. We also show that the vanishing classical vacuum energy of the SO(8192) unoriented bosonic open-string theory does not receive any tree-level corrections from the tadpole resummation. This result is consistent with the fact that this (unstable) configuration is free from tadpoles of massless closed-string modes, although there is a tadpole of the closed string tachyon. The application of this method to superstring models with broken supersymmetry is also discussed.     

A Sharpened Nuclearity Condition for Massless Fields

A recently proposed phase space condition which comprises information about the vacuum structure and timelike asymptotic behavior of physical states is verified in massless free field theory. There follow interesting conclusions about the momentum transfer of local operators in this model.     

On the equivalence of the Lagrangians of massless dirac and supersymmetrical particles

The classical equivalence between the Lagrangians of massless spinning and supersymmetrical particles presented in terms of u _A and Grassmannian _A Weyl spinor variables is established. It is shown that the condition of the inverse Higgs effect for a spinor invariant superform leads to the extension of the Penrose representation and the realization of fermionic string variables in terms of superstring variables. New superfield formulations of the actions for particles and strings invariant under local (world-sheet) and global (spacetime) supersymmetrics are suggested.     

Mass Inequalities in Vectorial Gauge.Theory Based on Compact Semi-simple Lie Group

The mass inequalities valid in the vectorial gauge theory based on a simple group can be generalized to the case with a compact semi-simple Lie group if the vacuum angle is assumed to be zero. A new meaning of these inequalities lies in that a vectorial Aavor gauge symmetry can not be spontaneously broken by the color condensates among the fermions with nonzero bare masses. In the semi-simple group case the vacuum angle could be naturally set to be zero only if there are massless fermions assigned in special representations of the group. This provides the possibility to break down the mass inequalities and could find some physical applications.     

Surface vacuum energy and stresses for a brane in de Sitter spacetime

Vacuum expectation values of the surface energy–momentum tensor is investigated for a massless scalar field obeying mixed boundary condition on a brane in de Sitter bulk. To generate the corresponding vacuum surface densities we use the conformal relation between de Sitter and Rindler spacetimes.     

Adjoint QCD1 + 1 in light-cone gauge, quantized at equal time

SU (2) gauge theory coupled to massless fermions in the adjoint representation is quantized in light-cone gauge by imposing the equal-time canonical algebra. The theory is defined on a space-time cylinder with “twisted” boundary conditions, periodic for one color component (the diagonal 3-component) and antiperiodic for the other two. The focus of the study is on the non-trivial vacuum structure and the fermion condensate. It is shown that the indefinite-metric quantization of free gauge bosons is not compatible with the residual gauge symmetry of the interacting theory. A suitable quantization of the unphysical modes of the gauge field is necessary in order to guarantee the consistency of the subsidiary condition and allow the quantum representation of the residual gauge symmetry of the classical Lagrangian: the 3-color component of the gauge field must be quantized in a space with an indefinite metric while the other two components require a positive-definite metric. The contribution of the latter to the free Hamiltonian becomes highly pathological in this representation, but a larger portion of the interacting Hamiltonian can be diagonalized, thus allowing perturbative calculations to be performed. The vacuum is evaluated through second order in perturbation theory and this result is used for an approximate determination of the fermion condensate.     

Evidence for heterotic - Type I string duality

A study is made of the implications of heterotic string T-duality and extended gauge symmetry for the conjectured equivalence of heterotic and Type I superstrings. While at first sight heterotic string world-sheet dynamics appears to conflict with Type I perturbation theory, a closer look shows that Type I perturbation theory “miraculously” breaks down, in some cases via novel mechanisms, whenever the heterotic string has massless particles not present in Type I perturbation theory. This strongly suggests that the two theories actually are equivalent. As further evidence in the same direction, we show that the Dirichlet one-brane of Type I string theory has the same world-sheet structure as the heterotic string.     

Our world as an intersection of walls and a string

A solution of Einstein equations is obtained for our four-dimensional world as an intersection of a wall and a string-like defect in seven-dimensional spacetime with a negative cosmological constant. A matter energy–momentum tensor localized on the wall and on the string is needed. A single massless graviton is found and is localized around the intersection. The leading correction to the gravitational Newton potential from massive spin 2 graviton is found to be almost identical to that of a wall in five dimensions, contrary to the case of a string in six dimensions. The generalization to the intersection of a string and n orthogonally intersecting walls is also obtained and a similar result is found for the gravitational potential.     

考虑绳及圆盘质量时对Atwood机运动的影响

求解Atwood机动力学问题,教材中通常把绳子及滑轮当做理想模型(不考虑它们的质量).本文利用动力学的方法,考虑了Atwood机中滑轮、绳的质量,对其实际情况下的运动进行了求解,分析了两者质量及重物的初位移对系统运动的影响,指出了与理想模型之间的差异.     

Spontaneous breaking of C-invariance in a Friedmann universe with matter

This paper considers the theory of a massless complex scalar field in an isotropic nonstationary Friedmann universe, where account of the self-interaction leads to spontaneous symmetry breaking relative to certain transformations. Consideration of the exact solutions to the self-consistent Einstein equations and the equations of the complex field in an open Friedmann universe in the presence of dust can lead to a nonzero macroscopic vacuum charge density, which is interpreted by the author as a breaking of C-invariance by the vacuum.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 22–26, July, 1984.In conclusion, the author would like to thank G. G. Ivanov for the general formulation of the problem, and also A. A. Grib for discussion of the results obtained.