Recent content by wam_mi

The existence of the cosmological constant in the field equations is by itself inconsistant with the metric being flat because the condition g_{\mu\nu}\rightarrow \eta_{\mu\nu} so that T_{\mu\nu}\rightarrow 0 will no longer hold. This can also be understood from the property of the...

Dear all, In flat conformal space-time, e.g. \quad g_{\alpha \beta} = e^{4\kappa} \eta_{\alpha \beta} where \kappa is some function of space-time coordinates. What sort of paths do photons and massive particles follow? Could anyone describe their paths with some analagy or a...

I read the following on wiki "The Einstein's field equation is a tensor equation relating a set of symmetric 4 x 4 tensors. It is written here using the abstract index notation. Each tensor has 10 independent components. Given the freedom of choice of the four spacetime coordinates, the...

Homework Statement How do I show the following metric have time-like geodesics, if \theta and R are constants ds^{2} = R^{2} (-dt^{2} + (cosh(t))^{2} d\theta^{2}) Homework Equations v^{a}v_{a} = -1 for time-like geodesic, where v^{a} is the tangent vector along the curve The Attempt at a...

Hi there, I am learning the basics of QFT at the moment. Could someone explain to me, in the case for any number of scalar fields, the difference between correlation functions and scattering amplitudes please? Correlation functions <0|T(\phi_{1}...\phi{n})|0> Does one always write the...

I think I got it. Is it correct to say if one puts the inner product into the parallel transport expression, one finds that the expression vanishes as parallel transport preserves the inner product such that the character of the geodesic never changes. Thanks

Homework Statement If the geodesic is space-like somewhere, show that the geodesic is space-like everywhere. Homework Equations Geodesic equation: \ddot{X}^{\mu}+\Gamma^{\mu}_{\alpha \beta}\dot{X}^{\alpha}\dot{X}^{\beta} = 0 The Attempt at a Solution I looked at the metric...

Homework Statement Hello, Consider a rod of proper length l_{0}. Prove/Show that there is no length contraction if an observer moves perpendicular to the direction of the rod. Homework Equations l = l_{0}/\gamma where \gamma is the usual relativistic vector The Attempt at a...

The limit (R --> 0) of type IIA superstrings is equivalent Hi there, The limit (R --> 0) of type IIA superstrings is equivalent to the limit (R --> infty) of type IIB theory. Could someone explain how this works? Thanks

Hi there, It is said that the Virasoro algebra/constraint is the most important algebra is string theory. (i) Why is that? (ii) How is it related to the world-sheet conformal symmetry? (iii) How do I see that the Virasoro constraints are the vanishing of the stress tensor, which can...

Hi there, I recently read about the construction of the Nambu-Goto action by looking at the proper area of the world-sheet. However, when one varies the action with an arbitrary space-time coordinate (here I treat it in Minkowski space-time X^(\mu)), there appears three terms and some of them...

Dear all, I have recently read the effects of T-duality of both closed and open strings (Zwiebach 2009, Johnson 2003) and found it very interesting indeed. However, I found it difficult to understand the concept of Wilson lines. Could someone please explain me the idea and concept of Wilson...

Hi there, Could someone explain to me what a moduli space is. (i) What does the generating group O(d, d,R) mean? (ii) Why is it then the modular space is written as O(d,d,R)/O(d,R)×O(d,R) What role does the division play here? Thanks a lot!

Hi there, Where can I find some review articles about space-time supersymmetry? Cheers!

Hi there, What is the difference between Space-time Supersymmetry and Supersymmetry? Is Space-time Supersymmetry the same thing as Supergravity? What is Supergravity... All these terms make me very confused... Thanks a lot!