scholarly journals The effective potential in nonconformal gauge theories

2017 ◽  
Vol 32 (02n03) ◽  
pp. 1750003 ◽  
Author(s):  
F. T. Brandt ◽  
F. A. Chishtie ◽  
D. G. C. McKeon
Keyword(s):  
Effective Potential ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Mass Term ◽  
Coupling Constants ◽  
Tree Level ◽  
Massless Scalar ◽  
Classical Action ◽  
Expectation Value ◽  
Logarithmic Corrections

By using the renormalization group (RG) equation it has proved possible to sum logarithmic corrections to quantities that arise due to quantum effects in field theories. In particular, the effective potential [Formula: see text] in the Standard Model in the limit that there are no massive parameters in the classical action (the “conformal limit”) has been subject to this analysis, as has the effective potential in a scalar theory with a quartic self-coupling and in massless scalar electrodynamics. Having multiple coupling constants and/or mass parameters in the initial action complicates this analysis, as then several mass scales arise. We show how to address this problem by considering the effective potential in a Yukawa model when the scalar field has a tree-level mass term. In addition to summing logarithmic corrections by using the RG equation, we also consider the consequences of the condition [Formula: see text] where [Formula: see text] is the vacuum expectation value of the scalar. If [Formula: see text] is expanded in powers of logarithms that arise, then it proves possible to show that either [Formula: see text] is zero or that [Formula: see text] is independent of the scalar. (That is, either there is no spontaneous symmetry breaking or the vacuum expectation value is not determined by minimizing [Formula: see text] as [Formula: see text] is “flat”.)

scholarly journals THE RENORMALIZATION GROUP IMPROVED EFFECTIVE POTENTIAL IN MASSLESS MODELS

2005 ◽  
Vol 20 (29) ◽  
pp. 2215-2226 ◽  
Author(s):  
F. T. BRANDT ◽  
F. A. CHISHTIE ◽  
D. G. C. MCKEON
Keyword(s):  
Renormalization Group ◽  
Effective Potential ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Background Field ◽  
Massless Scalar ◽  
Expectation Value

The effective potential V is considered in massless [Formula: see text] theory. The expansion of V in powers of the coupling λ and of the logarithm of the background field ϕ is reorganized in two ways; first as a series in λ alone, then as a series in ln ϕ alone. By applying the renormalization group (RG) equation to V, these expansions can be summed. Using the condition V′(v)=0 (where v is the vacuum expectation value of ϕ) in conjunction with the expansion of V in powers of ln ϕ fixes V provided v≠0. In this case, the dependence of V on ϕ drops out and V is not analytic in λ. Massless scalar electrodynamics is considered using the same approach.

COLOR CONFINEMENT AND FINITE TEMPERATURE QCD PHASE TRANSITION

2004 ◽  
Vol 19 (02) ◽  
pp. 271-285 ◽  
Author(s):  
H. C. PANDEY ◽  
H. C. CHANDOLA ◽  
H. DEHNEN
Keyword(s):  
Phase Transition ◽  
Critical Temperature ◽  
Effective Potential ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Zero Temperature ◽  
Expectation Value ◽  
Qcd Phase Transition ◽  
Qcd Vacuum ◽  
Color Confinement

We study an effective theory of QCD in which the fundamental variables are dual magnetic potentials coupled to the monopole field. Dual dynamics are then used to explain the properties of QCD vacuum at zero temperature as well as at finite temperatures. At zero temperature, the color confinement is realized through the dynamical breaking of magnetic symmetry, which leads to the magnetic condensation of QCD vacuum. The flux tube structure of SU(2) QCD vacuum is investigated by solving the field equations in the low energy regimes of the theory, which guarantees dual superconducting nature of the QCD vacuum. The QCD phase transition at finite temperature is studied by the functional diagrammatic evaluation of the effective potential on the one-loop level. We then obtained analytical expressions for the vacuum expectation value of the condensed monopoles as well as the masses of glueballs from the temperature dependent effective potential. These nonperturbative parameters are also evaluated numerically and used to determine the critical temperature of the QCD phase transition. Finally, it is shown that near the critical temperature (Tc≃0.195 GeV ), continuous reduction of vacuum expectation value (VEV) of the condensed monopoles caused the disappearance of vector and scalar glueball masses, which brings a second order phase transition in pure SU(2) gauge QCD.

scholarly journals LIGHT-CONE FLUCTUATIONS AND THE RENORMALIZED STRESS TENSOR OF A MASSLESS SCALAR FIELD

2013 ◽  
Vol 28 (01) ◽  
pp. 1350001 ◽  
Author(s):  
V. A. DE LORENCI ◽  
G. MENEZES ◽  
N. F. SVAITER
Keyword(s):  
Scalar Field ◽  
Light Cone ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Flat Space ◽  
Massless Scalar ◽  
Energy Tensor ◽  
Massless Scalar Field ◽  
Expectation Value ◽  
Stress Energy

We investigate the effects of light-cone fluctuations over the renormalized vacuum expectation value of the stress–energy tensor of a real massless minimally coupled scalar field defined in a (d+1)-dimensional flat space–time with topology [Formula: see text]. For modeling the influence of light-cone fluctuations over the quantum field, we consider a random Klein–Gordon equation. We study the case of centered Gaussian processes. After taking into account all the realizations of the random processes, we present the correction caused by random fluctuations. The averaged renormalized vacuum expectation value of the stress–energy associated with the scalar field is presented.

scholarly journals Local zeta regularization and the scalar Casimir effect IV: The case of a rectangular box

2016 ◽  
Vol 31 (04n05) ◽  
pp. 1650003 ◽  
Author(s):  
Davide Fermi ◽  
Livio Pizzocchero
Keyword(s):  
Casimir Effect ◽  
Arbitrary Dimension ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Massless Scalar ◽  
Energy Tensor ◽  
Massless Scalar Field ◽  
Stress Energy Tensor ◽  
Expectation Value ◽  
Stress Energy

Applying the general framework for local zeta regularization proposed in Part I of this series of papers, we compute the renormalized vacuum expectation value of several observables (in particular, of the stress–energy tensor) for a massless scalar field confined within a rectangular box of arbitrary dimension.

Radiation from a moving mirror in two dimensional space-time: conformal anomaly

1976 ◽  
Vol 348 (1654) ◽  
pp. 393-414 ◽  
Keyword(s):  
Particle Production ◽  
Dimensional Space ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Momentum Tensor ◽  
Conformal Anomaly ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Two Dimensional ◽  
Expectation Value

The energy-momentum tensor is calculated in the two dimensional quantum theory of a massless scalar field influenced by the motion of a perfectly reflecting boundary (mirror). This simple model system evidently can provide insight into more sophisticated processes, such as particle production in cosmological models and exploding black holes. In spite of the conformally static nature of the problem, the vacuum expectation value of the tensor for an arbitrary mirror trajectory exhibits a non-vanishing radiation flux (which may be readily computed). The expectation value of the instantaneous energy flux is negative when the proper acceleration of the mirror is increasing, but the total energy radiated during a bounded mirror motion is positive. A uniformly accelerating mirror does not radiate; however, our quantization does not coincide with the treatment of that system as a ‘static universe’. The calculation of the expectation value requires a regularization procedure of covariant separation of points (in products of field operators) along time-like geodesics; more naïve methods do not yield the same answers. A striking example involving two mirrors clarifies the significance of the conformal anomaly.

Global symmetries and Noether’s theorem

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Global Symmetries ◽  
Symmetry Transformation ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Quantum Field ◽  
Expectation Value ◽  
Minkowski Space Time ◽  
Integral Measure ◽  
Colour Charge ◽  
Internal Symmetries

Noethers theorem shows that continuous global symmetries lead classically to conservation laws. Such symmetries can be divided into spacetime and internal symmetries. The invariance of Minkowski space-time under global Poincaré transformations leads to the conservation of the four-momentum and the total angular momentum. Examples for conserved charges due to internal symmetries are electric and colour charge. The vacuum expectation value of a Noether current is shown to beconserved in a quantum field theory if the symmetry transformation keeps the path-integral measure invariant.

scholarly journals Vacuum Polarization in a Zero-Width Potential: Self-Adjoint Extension

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 127
Author(s):  
Yuri V. Grats ◽  
Pavel Spirin
Keyword(s):  
Scalar Field ◽  
Vacuum Polarization ◽  
Dimensional Regularization ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Field Approximation ◽  
Dimensional Euclidean Space ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Adjoint Extension

The effects of vacuum polarization associated with a massless scalar field near pointlike source with a zero-range potential in three spatial dimensions are analyzed. The “physical” approach consists in the usage of direct delta-potential as a model of pointlike interaction. We use the Perturbation theory in the Fourier space with dimensional regularization of the momentum integrals. In the weak-field approximation, we compute the effects of interest. The “mathematical” approach implies the self-adjoint extension technique. In the Quantum-Field-Theory framework we consider the massless scalar field in a 3-dimensional Euclidean space with an extracted point. With appropriate boundary conditions it is considered an adequate mathematical model for the description of a pointlike source. We compute the renormalized vacuum expectation value ⟨ϕ2(x)⟩ren of the field square and the renormalized vacuum averaged of the scalar-field’s energy-momentum tensor ⟨Tμν(x)⟩ren. For the physical interpretation of the extension parameter we compare these results with those of perturbative computations. In addition, we present some general formulae for vacuum polarization effects at large distances in the presence of an abstract weak potential with finite-sized compact support.

scholarly journals THE TACHYON FIELD BELOW THE MASS BARRIER

1994 ◽  
Vol 09 (20) ◽  
pp. 3497-3502 ◽  
Author(s):  
D.G. BARCI ◽  
C.G. BOLLINI ◽  
M.C. ROCCA
Keyword(s):  
Green Function ◽  
Eigenvalue Problem ◽  
Plane Wave ◽  
Time Evolution ◽  
Mass Parameter ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Tachyon Field ◽  
Expectation Value ◽  
Wave Solutions

We consider a tachyon field whose Fourier components correspond to spatial momenta with modulus smaller than the mass parameter. The plane wave solutions have then a time evolution which is a real exponential. The field is quantized and the solution of the eigenvalue problem for the Hamiltonian leads to the evaluation of the vacuum expectation value of products of field operators. The propagator turns out to be half-advanced and half-retarded. This completes the proof4 that the total propagator is the Wheeler Green function.4,7

THE TWISTED EUCLIDEAN GREEN’S FUNCTION IN THE SPACETIME OF A COSMIC STRING

1992 ◽  
Vol 01 (02) ◽  
pp. 371-377 ◽  
Author(s):  
B. LINET
Keyword(s):  
Green’S Function ◽  
Green's Function ◽  
Minkowski Spacetime ◽  
Vacuum Expectation ◽  
Vacuum Expectation Value ◽  
Massive Scalar ◽  
Elementary Functions ◽  
Integral Expression ◽  
Massive Scalar Field ◽  
Expectation Value

In a conical spacetime, we determine the twisted Euclidean Green’s function for a massive scalar field. In particular, we give a convenient form for studying the vacuum averages. We then derive an integral expression of the vacuum expectation value <Φ2(x)>. In the Minkowski spacetime, we express <Φ2(x)> in terms of elementary functions.

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