56092735
Two-branes with variable tension model and the effective Newtonian constant
It is shown that, in the two brane time variation model framework, if the hidden brane tension varies according to the phenomenological Eoetvoes law, the visible brane tension behavior is such that its time derivative is negative in the past and positive after a specific time of cosmological evolution. This behavior is interpreted in terms of a useful mechanical system analog and its relation with the variation of the Newtonian (effective) gravitational ''constant'' is explored.
56078295
Towards a hybrid compactification with a scalar–tensor global cosmic string
We derive a solution of the gravitational equations which leads to a braneworld scenario in six dimensions, using a global cosmic string solution in a low energy effective string theory framework. The final spacetime is composed by one warped brane with topology and a power law warp factor, and one non-compact extra dimension transverse to the brane; by looking at the current experimental bounds, we find a range of parameters in which, if the on-brane dimension has an acceptable size, it does not solve the hierarchy problem. In another example, this problem is smoothed by means of the Brans–Dicke parameter.
117828168
Possible Generalizations within Braneworld Scenarios: Torsion fields
In this Chapter we introduce the aspects in which torsion can influence the formalism of braneworld scenarios in general, and also how it is possible to measure such kind of effects, namely, for instance, the blackstring transverse area corrections and variation of quasar luminosity due to those corrections. We analyze the projected effective Einstein equation in a 4-dimensional arbitrary manifold embedded in a 5-dimensional Riemann-Cartan manifold. The Israel-Darmois matching conditions are investigated, in the context where the torsion discontinuity is orthogonal to the brane. Unexpectedly, the presence of torsion terms in the connection does not modify such conditions whatsoever, despite of the modification in the extrinsic curvature and in the connection. Then, by imposing the Z2-symmetry, the Einstein equation obtained via Gauss-Codazzi formalism is extended, in order to now encompass the torsion terms. We also show that the factors involving contorsion change drastically the effective Einstein equation on the brane, as well as the effective cosmological constant. Also, we present gravitational aspects of braneworld models endowed with torsion terms both in the bulk and on the brane. In order to investigate a conceivable and measurable gravitational effect, arising genuinely from bulk torsion terms, we analyze the variation in the black hole area by the presence of torsion. Furthermore, we extend the well known results about consistency conditions in a framework that incorporates brane torsion terms. It is shown, in a rough estimate, that the resulting effects are generally suppressed by the internal space volume.
118609176
Static domain wall in braneworld gravity
In this paper we consider a static domain wall inside a 3-brane. Different from the standard achievement obtained in General Relativity, the analysis performed here gives a consistency condition for the existence of static domain walls in a braneworld gravitational scenario. Also the behavior of the domain wall’s gravitational field in the newtonian limit is shown.
119652642
Black holes in realistic branes: Black string-like objects?
Abstract A realistic model describing a black string-like object in an expanding Universe is analyzed in the context of the McVittieʼs solution of the Einstein field equations. The bulk metric near the brane is provided analogously to previous solutions for black strings. In particular, we show that at least when the Hubble parameter on the brane is positive, a black string-like object seems to play a fundamental role in the braneworld scenario, generalizing the standard black strings in the context of a dynamical brane.
119686824
Regular Bulk Solutions and Black Strings from Dynamical Braneworlds with Variable Tension
Regular black strings solutions associated to a dynamical Friedmann-Robertson-Walker braneworld are obtained as a particular case of a regular bulk metric, in the context of a variable brane tension. By analyzing the 5D Kretschmann invariants, we show that the variable brane tension is capable to remove bulk singularities, along some eras of the evolution of the Universe. In particular, the black string time-dependent profile in the bulk is analyzed in the context of the McVittie metric on an E\"otv\"os fluid braneworld, wherein the fluid dynamical brane tension depends on the brane temperature. The whole bulk is shown to be regular for a Universe dominated by non-relativistic matter or by relativistic matter/radiation, as the cosmological time elapses. In a particular case the associated black strings are shown to have finite extension along the extra dimension, what prominently modify the higher-dimensional physical singularities. For a Universe dominated by matter or radiation, we show that the brane singularities are removed along the extra dimension, as an effect of the variable brane tension, corresponding also to the vanishing of the black string horizon. In this case there is a regular solution in the bulk. We show further that no additional physical singularity is introduced in the bulk when the Universe is dominated by a cosmological constant.
118889338
Phenomenological aspects of CP violation
We present a pedagogical review of the phenomenology of CP violation, with emphasis on B decays. Main topics include the phenomenology of neutral meson systems, CP violation in the Standard Model of electroweak interactions, and B decays. We stress the importance of the reciprocal basis, sign conventions, rephasing invariance, general definitions of the CP transformation and the spurious phases they bring about, CP violation as originating from the clash of two contributions, the rho-eta plane, the four phases of a generalized CKM matrix, and the impact of discrete ambiguities. Specific B decays are included in order to illustrate some general techniques used in extracting information from B physics experiments. We include a series of simple exercises. The style is informal.
40594950
On the use of the reciprocal basis in neutral meson mixing
In the presence of CP violation, the effective Hamiltonian matrix describing a neutral meson anti-meson system does not commute with its hermitian conjugate. As a result, this matrix cannot be diagonalized by a unitary transformation and one needs to introduce a reciprocal basis. Although known, this fact is seldom discussed and almost never used. Here, we use this concept to highlight a parameterization of the Hamiltonian matrix in terms of physical observables, and we show that using it reduces a number of long and tedious derivations into simple matrix multiplications. These results have a straightforward application for propagation in matter. We also comment on the (mathematical) relation with neutrino oscillations.
16424986
Detecting new physics contributions to the D0 - anti-D0 mixing through their effects on B decays
New physics effects may yield a detectable mass difference in the D0-D0bar system, Delta m_D. Here we show that this has an important impact on some B --> D decays. The effect involves a new source of CP violation, which arises from the interference between the phases in the B --> D decays and those in the D0-D0bar system. This interference is naturally large. New physics may well manifest itself through Delta m_D contributions to these B decays.
120761568
Approximate flavor symmetries in the lepton sector
Approximate flavor symmetries in the quark sector have been used as a handle on physics beyond the standard model. Because of the great interest in neutrino masses and mixings and the wealth of existing and proposed neutrino experiments it is important to extend this analysis to the leptonic sector. We show that in the seesaw mechanism the neutrino masses and mixing angles do not depend on the details of the right-handed neutrino flavor symmetry breaking, and are related by a simple formula. We propose several [ital Ansa]$[ital uml]---[ital tze] which relate different flavor symmetry-breaking parameters and find that the MSW solution to the solar neutrino problem is always easily fit. Further, the [nu][sub [mu]-][nu][sub [tau]] oscillation is unlikely to solve the atmospheric neutrino problem and, if we fix the neutrino mass scale by the MSW solution, the neutrino masses are found to be too small to close the Universe.
30443539
Reparametrization invariance of B decay amplitudes and implications for new physics searches in B decays
When studying $B$ decays within the standard model (SM), it is customary to use the unitarity of the CKM matrix in order to write the decay amplitudes in terms of only two of the three weak phases which appear in the various diagrams. Occasionally, it is mentioned that those two weak phases can be used in order to describe any decay amplitude, even beyond the standard model. Here we point out that, when describing a generic decay amplitude, the two weak phases can be chosen completely at will, and we study the behavior of the decay amplitudes under changes in the two weak phases chosen as a basis. Of course, physical observables cannot depend on such reparametrizations. This has an impact on discussions of the SM and on attempts to parametrize new physics effects in the decay amplitudes. We illustrate these issues by looking at $B\ensuremath{\rightarrow}\ensuremath{\psi}{K}_{S}$ and the isospin analysis in $B\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}$.