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I am an experimentalist. For me the beauty of the Standard Model of particle physics lies in that it encompasses successfully, in a mathematical manner, the innumerable experimental data of the last sixty years and more. The pros for both proposed theories for gravity are the quantization of gravity, a long sought after holy grail. I am biased by ...


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Radioactivity is a result of unstable atoms. That is, an atom that either has too many protons, neutrons or electrons to stay stable. Using Quantum Mechanics and looking at the overlap of wavefunctions in time, it should be possible to predict the rate of radioactive decay. But I believe you and I would be long dead before today's computers would finish a ...


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No, it's not possible. The reason is that string theory is a quantum theory. That means it includes all of the properties of quantum theory among its basic assumptions. That includes the Born rule, which relates wavefunctions to stochastic probabilities ("randomness") when measurements are made. Because string theory includes quantum randomness as an ...


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For Supersymmetry: -Introduction to Supersymmetry, (Müller-Kirsten, Wiedemann) It's very detailed in every aspect, from graded algebras to the lagrangian of Supersymmetry and symmetry breaking.To be supplemented with something on phenomenology (see below) -Supersymmetry and Supergravity, (Wess, Bagger) Very advanced, but a bit obscure. To be ...


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As stated in another answer already, your definition of the holographic principle is misleading. More precisely, the holographic principle says the following: A theory of quantum gravity in a compact space should be equivalent to some theory on the boundary of this space. This statement (which is a conjecture) is motivated from the result of Bekenstein and ...


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A "fifth force" can be given by a scalar field. This field arises in many theories, for example from the dilaton scalar field of string theory, that is non minimally coupled to $R$ in the action. In the low energy limit we can phenomenologically treat string theory as a Scalar Tensor Theories of Gravitation (see the Wikipedia Link for details) in which you ...


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some theories propose that the infalton field is actually the same a dark energy,, if that were correct, then we would have a fifth field (force might not be correct in this context) that ineracts with the other four. And who knows what else, dark matter might have lots of forces that are invisible to us because they just do not inetract with the four we do. ...


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Brian Greene talks of many more types of multiverses...holographic, extra dimensional, simulated etc. It is also possible our universe is only a construct of our consciousness in which case consciousness would vary in a different universe..but that is in the realm of philosophy. Higgs field variation- a basic energy field value creating the constants and ...


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It is conjectured that they are equivalent. Regarding your two remarks notice that: 1) In string theory the extra dimensions are curled and small enough that we cannot perceive them. So for any practical everyday purposed string theory results in a 3D world. 2) the quote: Everything is happening in a surface and our three-dimensionality is an illusion of ...


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It is a pseudoproblem of definition. Some people define universe as everything that could ever possible exist, to them the word multiverse is an oxymoron. But those who like to use the idea of a multiverse, use it encompassing different things depending on context. For instance, Max tegmark defines 4 different levels of universes/multiverses: Level I: ...


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As far as I know, "a" Universe is caracterised by fundemental constants such as the speed of light, Newton's gravitationnal constant, the Planck constant and so on. You could distinguish between two different universe from the variation of these values I think.


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A simple way to see why the systems you describe are not identical is to recognize that a $D0$ brane carries R-R charge which sources a one-form potential, while the closed string is uncharged.


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If one calculates expectation value $\langle\Psi| M^2|\Psi\rangle$ of the mass-square operator $M^2$ of the state $|\Psi\rangle~=~ \alpha^j_{-1}| 0; p\rangle $, then the level-matching condition (2.25) would be violated.


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Define $$ N \equiv \sum_{i=0}^{D-2} \alpha_{-n}^i \alpha_n^i,~~~~{\tilde N} \equiv \sum_{i=0}^{D-2} {\tilde \alpha}_{-n}^i {\tilde \alpha}_n^i $$ The formula you have written tells us un particular that for any state, we must have $N = {\tilde N}$. This condition is known as the level-matching condition. The state $\alpha^i_{-1} |0;k\rangle$ has $N = 1$ but ...


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Both $h$ and $\tilde{h}$ are usually called weights. Their sum, $\Delta=h+\tilde{h}$ is the (scaling) dimension of the operator, while the difference, $s=h-\tilde{h}$ is called the spin. This is due to their association with scale transformations (dilatations) and rotations, respectively. To see this, note that the dilatation operator is given by ...


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One comes to this conclusion due to the fact that the contraction of a symmetric tensor with an antisymmetric one vanishes. Writing down the loop diagrams involves a contraction of both vertices. If you get expressions proportional to $\epsilon_{\mu\nu}\eta^{\mu\nu}$, this will be zero due to the fact that the metric is symmetric and the epsilon tensor is ...


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It's the chain rule: $$ \partial_x f(y(x)) = \partial_y f(y(x)) \cdot \partial_x y(x)$$ Your vector field $A^\mu$ depends on the worldsheet coordinates only through the worldsheet coordinates $x^\mu$. Thus, when how $A^\mu$ behaves under an infinitesimal shift on the world-sheet you need to take into account how $A^\mu$ depends on $z$ - that's $\partial_z ...



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