10853970
Rare B decays in the standard model
Abstract We discuss the electromagnetic-penguin-dominated radiative B decays B → X s + γ , B ±(0) → K ∗±(0) + γ , and B s → φ + γ in the context of the Standard Model (SM) and their Cabibbo-Kobayashi-Maskawa (CKM)-suppressed counterparts, B → X d + γ , B ± → ϱ ± + γ , B 0 → ( ϱ 0 , ω ) + γ , and B s → K ∗0 + γ , using QCD sum rules for the exclusive decays. The importance of these decays in determining the parameters of the CKM matrix [1] is emphasized. The semileptonic decays B → X s l + l − are also discussed in the context of the SM and their role in determining the Wilson coefficients of the effective theory is stressed. Comparison with the existing measurements are made and SM-based predictions for a large number of rare B decays are presented.
119012010
$B$ Decays, Flavour Mixings and CP Violation in the Standard Model
These lectures review the progress made in our present understanding of $B$ decays. The emphasis here is on applications of QCD to $B$ decays and the attendant perturbative and non-perturbative uncertainties, which limit present theoretical precision in some cases but the overall picture that emerges is consistent with the standard model (SM). This is illustrated by quantitatively analyzing some of the key measurements in $B$ physics.
13281897
Majorana neutrinos and same-sign dilepton production at LHC and in rare meson decays
Abstract. We discuss same-sign dilepton production mediated by Majorana neutrinos in high-energy proton–proton collisions $pp\rightarrow \ell^+ \ell^{\prime +}X$ for $\ell, \ell^\prime = e, \mu, \tau$ at the LHC energy $ s^{1/2} =14$ TeV, and in the rare decays of the $K, D, D_s$, and B mesons of the type $M^+\rightarrow M^{\prime -}\ell ^+\ell ^{\prime+}$. For the pp reaction, assuming one heavy Majorana neutrino of mass $m_N$, we present discovery limits in the $\left(m_N,\left|U_{\ell N}U_{\ell^\prime N}\right|\right)$ plane where $U_{\ell N}$ are the mixing parameters. Taking into account the present limits from low-energy experiments, we show that at LHC one has sensitivity to heavy Majorana neutrinos up to a mass $m_N\leq 2--5$ TeV in the dilepton channels $\mu\mu, \tau\tau$, and $\mu\tau$, but the dilepton states $e\ell$ will not be detectable due to the already existing constraints from neutrinoless double beta decay. We work out a large number of rare meson decays, both for the light and heavy Majorana neutrino scenarios, and argue that the present experimental bounds on the branching ratios are too weak to set reasonable limits on the effective Majorana masses.
120435310
A calculation of the electromagnetic vacuum polarization in lattice QCD
Abstract We present a calculation of the electromagnetic current vacuum polarization in the framework of lattice QCD. A 16th order hopping-parameter expansion of 〈 J em μ J em μ 〉 0 is reported on an 8 4 lattice. It gives a reasonable description of the mass m J ψ and the electromagnetic current-vector meson coupling constant f J ψ , in the vector meson dominance approximation.
16422980
Rare radiative b decays in the standard model
A status report on the theory and phenomenology of rare radiative $B$ decays in the standard model is presented with emphasis on the measured decays $B \to X_s \gamma$ and $B \to K^* \gamma$. Standard model is in agreement with experiments though this comparison is not completely quantitative due to imprecise data and lack of the complete next-to-leading order contributions to the decay rates. Despite this, it is possible to extract non-perturbative parameters from the shape of the photon energy spectrum in $B \to X_s \gamma$, such as the $b$-quark mass and the kinetic energy of the $b$ quark in $B$ hadron. The measured decay rate $\BBGAMAXS =(2.32\pm 0.67) \times 10^{-4}$ can also be used to extract the CKM ratio $\absvts/\absvcb$, yielding $\absvts/\absvcb =1.10 \pm 0.43$. Issues bearing on the determination of the parameters of the CKM matrix from the CKM-suppressed decays $B \to X_d + \gamma$ and $B \to (\rho,\omega) + \gamma$ are also discussed. It is argued that valuable and independent constraints on the CKM matrix can be obtained from the measurements of these decays, in particular those involving neutral $B$-mesons (to appear in the Proceedings of the XXXth Rencontres de Moriond ``Electroweak Interactions and Unified Theories'', Les Arcs, France, March 1995).
10853970
Rare B decays in the standard model
Abstract We discuss the electromagnetic-penguin-dominated radiative B decays B → X s + γ , B ±(0) → K ∗±(0) + γ , and B s → φ + γ in the context of the Standard Model (SM) and their Cabibbo-Kobayashi-Maskawa (CKM)-suppressed counterparts, B → X d + γ , B ± → ϱ ± + γ , B 0 → ( ϱ 0 , ω ) + γ , and B s → K ∗0 + γ , using QCD sum rules for the exclusive decays. The importance of these decays in determining the parameters of the CKM matrix [1] is emphasized. The semileptonic decays B → X s l + l − are also discussed in the context of the SM and their role in determining the Wilson coefficients of the effective theory is stressed. Comparison with the existing measurements are made and SM-based predictions for a large number of rare B decays are presented.
46115571
A proposal for testing quantum gravity in the lab
Attempts to formulate a quantum theory of gravitation are collectively known as {\it quantum gravity}. Various approaches to quantum gravity such as string theory and loop quantum gravity, as well as black hole physics and doubly special relativity theories predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called generalized uncertainty principle (GUP). We have proposed a GUP consistent with string theory, black hole physics and doubly special relativity theories and have showed that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it suggests that the space that confines it must be quantized, and in fact that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this may signal the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale. Because this influences all the quantum Hamiltonians in an universal way, it predicts quantum gravity corrections to various quantum phenomena. Therefore, in the present work we compute these corrections to the Lamb shift, simple harmonic oscillator, Landau levels, and the tunneling current in a scanning tunneling microscope.
120051381
Discreteness of space from GUP II: Relativistic wave equations
Abstract Various theories of Quantum Gravity predict modifications of the Heisenberg Uncertainty Principle near the Planck scale to a so-called Generalized Uncertainty Principle (GUP). In some recent papers, we showed that the GUP gives rise to corrections to the Schrodinger equation, which in turn affect all quantum mechanical Hamiltonians. In particular, by applying it to a particle in a one-dimensional box, we showed that the box length must be quantized in terms of a fundamental length (which could be the Planck length), which we interpreted as a signal of fundamental discreteness of space itself. In this Letter, we extend the above results to a relativistic particle in a rectangular as well as a spherical box, by solving the GUP-corrected Klein–Gordon and Dirac equations, and for the latter, to two and three dimensions. We again arrive at quantization of box length, area and volume and an indication of the fundamentally grainy nature of space. We discuss possible implications.
118780957
Discreteness of space from the generalized uncertainty principle
Various approaches to Quantum Gravity (such as String Theory and Doubly Special Relativity), as well as black hole physics predict a minimum measurable length, or a maximum observable momentum, and related modifications of the Heisenberg Uncertainty Principle to a so-called Generalized Uncertainty Principle (GUP). We propose a GUP consistent with String Theory, Doubly Special Relativity and black hole physics, and show that this modifies all quantum mechanical Hamiltonians. When applied to an elementary particle, it implies that the space which confines it must be quantized. This suggests that space itself is discrete, and that all measurable lengths are quantized in units of a fundamental length (which can be the Planck length). On the one hand, this signals the breakdown of the spacetime continuum picture near that scale, and on the other hand, it can predict an upper bound on the quantum gravity parameter in the GUP, from current observations. Furthermore, such fundamental discreteness of space may have observable consequences at length scales much larger than the Planck scale.
118350400
The Generalized Uncertainty Principle and Quantum Gravity Phenomenology
In this article we examine a Generalized Uncertainty Principle which differs from the Heisenberg Uncertainty Principle by terms linear and quadratic in particle momenta, as proposed by the authors in an earlier paper. We show that this affects all Hamiltonians, and in particular those which describe low energy experiments. We discuss possible observational consequences. Further, we also show that this indicates that space may be discrete at the fundamental level.
119191368
Minimal length in quantum gravity, equivalence principle and holographic entropy bound
A possible discrepancy has been found between the results of a neutron interferometry experiment and quantum mechanics. This experiment suggests that the weak equivalence principle is violated at small length scales, which quantum mechanics cannot explain. In this paper, we investigated whether the generalized uncertainty principle (GUP), proposed by some approaches to quantum gravity such as string theory and doubly special relativity theories, can explain the violation of the weak equivalence principle at small length scales. We also investigated the consequences of the GUP on the Liouville theorem in statistical mechanics. We have found a new form of invariant phase space in the presence of GUP. This result should modify the density states and affect the calculation of the entropy bound of local quantum field theory, the cosmological constant, black body radiation, etc. Furthermore, such modification may have observable consequences at length scales much larger than the Planck scale. This modification leads to a -type correction to the bound of the maximal entropy of a bosonic field which would definitely shed some light on the holographic theory.