Lowest Kaluza-Klein Research Articles

Simplicity of AdS super Yang-Mills at one loop

We perform a systematic bootstrap analysis of four-point one-loop Mellin amplitudes for super gluons in AdS5 × S3 with arbitrary Kaluza-Klein weights. The analysis produces the general expressions for these amplitudes at extremalities two and three, as well as analytic results for many other special cases. From these results we observe remarkable simplicity. We find that the Mellin amplitudes always contain only simultaneous poles in two Mellin-Mandelstam variables, extending a previous observation in the simplest case with the lowest Kaluza-Klein weights. Moreover, we discover a substantial extension of the implication of the eight-dimensional hidden conformal symmetry, which goes far beyond the Mellin poles associated with the leading logarithmic singularities. This leaves only a small finite set of poles which can be determined on a case-by-case basis from the contributions of protected operators in the OPE.

Wavefunctions on S2 with flux and branes

We formulate a six dimensional U(1) gauge theory compactified on a (two dimensional) sphere S2 with flux and localized brane sources. Profiles of the lowest Kaluza-Klein (KK) wavefunctions and their masses are derived analytically. In contrast to ordinary sphere compactifications, the above setup can lead to the degeneracy of and the sharp localizations of the linearly independent lowest KK modes, depending on the number of branes and their tensions. Moreover, it can naturally accommodate CP violation in Yukawa interactions.

Spectrum universality properties of holographic Chern-Simons theories

We give a master formula for the spin-2 spectrum of a class of three-dimensional Chern-Simons theories at large N , with flavour group containing SU(3), that arise as infrared fixed points of the D2-brane worldvolume field theory and have AdS4 duals in massive type IIA supergravity. We use this formula to compute the spin-2 spectrum of the individual theories, discuss its supermultiplet structure and, for an mathcal{N} = 2 theory in this class, the spectrum of protected operators with spin 2. We also show that the trace of the Kaluza-Klein graviton mass matrix on the dual AdS4 solutions enjoys certain universality properties. These are shown to relate the class of AdS4 massive IIA solutions under consideration to a similar class of AdS4 solutions of D = 11 supergravity with the same symmetries. Finally, for the mathcal{N} = 2 AdS4 solution in this class, we study the entire spectrum at lowest Kaluza-Klein level and relate it to an analogue solution in D = 11 supergravity.

Higgs-radion phenomenology in stabilized RS models

An important general prediction of stabilized brane world models is the existence of a bulk scalar radion field, whose lowest Kaluza-Klein (KK) mode is the scalar particle called the radion. This field comes from the fluctuations of the metric in the extra dimension and the radion mass can be smaller than that of all the massive KK modes of the other particles propagating in the multidimensional bulk. Due to its origin, the radion and its KK tower couple to the trace of the energy-momentum tensor of the Standard Model. These fields have the same quantum numbers as the neutral Higgs field and can mix with the latter, if they are coupled. We present a short review of some aspects of Higgs-radion phenomenology in stabilized brane-world models. In particular, we discuss the possibility of explaining the 750 GeV excess by the production of a radion-dominated state.

Non-custodial warped extra dimensions at the LHC?

With the prospect of improved Higgs measurements at the LHC and at proposed future colliders such as ILC, CLIC and TLEP we study the non-custodial Randall-Sundrum model with bulk SM fields and compare brane and bulk Higgs scenarios. The latter bear resemblance to the well studied type III two-Higgs-doublet models. We compute the electroweak precision observables and argue that incalculable contributions to these, in the form of higher dimensional operators, could have an impact on the T-parameter. This could potentially reduce the bound on the lowest Kaluza-Klein gauge boson masses to the 5 TeV range, making them detectable at the LHC. In a second part, we compute the misalignment between fermion masses and Yukawa couplings caused by vector-like Kaluza-Klein fermions in this setup. The misalignment of the top Yukawa can easily reach 10%, making it observable at the high-luminosity LHC. Corrections to the bottom and tau Yukawa couplings can be at the percent level and detectable at ILC, CLIC or TLEP.

Higgs boson-radion similarity in production processes involving off-shell fermions

The appearance of the radion field, which is associated with the spin-0 metric fluctuations combined in some manner with the scalar stabilizing field, and of the radion, the corresponding lowest Kaluza-Klein (KK) mode, is a generic prediction of stabilized brane world models. In such models the radion plays the role of the dilaton, and its mass may be somewhat smaller than that of all the KK modes of other particles propagating in the multidimensional bulk. Due to its origin, the radion couples to the trace of the energy-momentum tensor of the Standard Model, the interaction Lagrangian of the radion and the Standard Model fermions being similar to that of the SM Higgs-fermion interactions except for additional terms, which come into play only in the case of off-shell fermions. In the present paper it is shown that all the contributions to perturbative amplitudes of physical processes due to these additional terms are canceled out for both massless and massive off-shell fermions. Thus the additional fermion-radion terms in the interaction Lagrangian do not alter any production and decay properties of the radion compared to those of the Higgs boson.

Fermions on thick branes in the background of sine-Gordon kinks

A class of thick branes in the background of sine-Gordon kinks with a scalar potential $V(\ensuremath{\phi})=p(1+\mathrm{cos}\frac{2\ensuremath{\phi}}{q})$ was constructed by R. Koley and S. Kar [Classical Quantum Gravity 22, 753 (2005)]. In this paper, in the background of the warped geometry, we investigate the issue of localization of spin-$1/2$ fermions on these branes in the presence of two types of scalar-fermion couplings: $\ensuremath{\eta}\overline{\ensuremath{\Psi}}\ensuremath{\phi}\ensuremath{\Psi}$ and $\ensuremath{\eta}\overline{\ensuremath{\Psi}}\mathrm{sin}\ensuremath{\phi}\ensuremath{\Psi}$. By presenting the mass-independent potentials in the corresponding Schr\"odinger equations, we obtain the lowest Kaluza-Klein modes and a continuous gapless spectrum of Kaluza-Klein states with ${m}^{2}>0$ for both types of couplings. For the Yukawa coupling $\ensuremath{\eta}\overline{\ensuremath{\Psi}}\ensuremath{\phi}\ensuremath{\Psi}$, the effective potential of the right chiral fermions for positive $q$ and $\ensuremath{\eta}$ is always positive; hence only the effective potential of the left chiral fermions could trap the corresponding zero mode. This is a well-known conclusion which is discussed extensively in the literature. However, for the coupling $\ensuremath{\eta}\overline{\ensuremath{\Psi}}\mathrm{sin}\ensuremath{\phi}\ensuremath{\Psi}$, the effective potential of the right chiral fermions for positive $q$ and $\ensuremath{\eta}$ is no longer always positive. Although the value of the potential at the location of the brane is still positive, it has a series of wells and barriers on each side, which ensures that the right chiral fermion zero mode could be trapped. Thus we may draw the following remarkable conclusion: for positive $\ensuremath{\eta}$ and $q$, the potentials of both the left and right chiral fermions could trap the corresponding zero modes under certain restrictions.

Stable skyrmions from extra dimensions

We show that skyrmions arising from compact five dimensional models have stable sizes. We numerically obtain the skyrmion configurations and calculate their size and energy. Although their size strongly depends on the magnitude of localized kinetic-terms, their energy is quite model-independent ranging between 50 - 65 times F-pi(2)/m(rho), where F-pi is the Goldstone decay constant and m(rho) the lowest Kaluza-Klein mass. These skyrmion configurations interpolate between small 4D YM instantons and 4D skyrmions made of Goldstones and a massive vector boson. Contrary to the original 4D skyrmion and previous 5D extensions, these configurations have sizes larger than the inverse of the cutoff scale and therefore they are trustable within our effective 5D approach. Such solitonic particles can have interesting phenomenological consequences as they carry a conserved topological charge analogous to baryon number.

Instanton calculations in the β-deformed AdS/CFT correspondence

We consider non-perturbative effects in the beta-deformed N=4 supersymmetric gauge theory in the context of the AdS/CFT correspondence. We concentrate on the correlators of the Yang-Mills operators which correspond to the lowest Kaluza-Klein modes propagating on the dual supergravity background found by Lunin and Maldacena in hep-th/0502086. In particular, we calculate all multi-instanton contributions to these correlators in the beta-deformed SYM and find a compelling agreement with the results expected in supergravity.

Spectrum of TeV particles in warped supersymmetric grand unification

In warped supersymmetric grand unification, XY gauge particles appear near the TeV scale along with Kaluza-Klein towers of the standard model gauge fields. In spite of this exotic low-energy physics, the successful gauge coupling unification prediction of the minimal supersymmetric standard model (MSSM) is preserved and proton decay is naturally suppressed. In this paper we study in detail the low-lying mass spectrum of superparticles and grand unified particles in this theory, taking supersymmetry breaking to be localized to the TeV brane. The masses of the MSSM particles, Kaluza-Klein modes, and XY states are all determined by two parameters, one that fixes the strength of the supersymmetry breaking and the other that sets the scale of the infrared brane. A particularly interesting result is that for relatively strong supersymmetry breaking, the XY gauginos and the lowest Kaluza-Klein excitations of the MSSM gauginos may both lie within reach of the CERN Large Hadron Collider, providing the possibility that the underlying unified gauge symmetry and the enhanced $N=2$ supersymmetry of the theory will both be revealed.

Constraints on the bulk standard model in the Randall-Sundrum scenario

We derive constraints on the Randall-Sundrum scenario with the standard model fields in the bulk. These result from tree level effects associated with the deformation of the zero mode wave functions of the W and the Z once electroweak symmetry is broken. Recently Cs\'aki, Erlich and Terning pointed out that this implies large contributions to electroweak oblique parameters. Here we find that when fermions are allowed in the bulk the couplings of the W and the Z to zero-mode fermions are also affected. We perform a fit to electroweak observables, assuming universal bulk fermion masses and including all effects, and find constraints that are considerably stronger than for the case with fermions localized in the low energy boundary. These put the lowest Kaluza-Klein excitation out of reach of the CERN Large Hadron Collider. We then relax the universality assumption and study the effects of flavor violation in the bulk and its possible signatures.

Kaluza–Klein excitations of W and Z at the LHC?

Deviations from standard electroweak physics arise in the framework of a Randall-Sundrum model, with matter and gauge fields in the bulk and the Higgs field localized on the TeV brane. We focus in particular on modifications associated with the weak mixing angle. Comparison with the electroweak precision data yields a rather stringent lower bound of about 10 TeV on the masses of the lowest Kaluza-Klein excitation of the W and Z bosons. With some optimistic assumptions the bound could be lowered to about 7 TeV.

Phenomenology of a stabilized modulus

We explore the phenomenology of a stabilized modulus field in the Randall-Sundrum scenario. It is found that if the large separation between branes arises from a small bulk scalar mass then the modulus (i.e. radion) is likely to be lighter than the lowest Kaluza-Klein excitations of bulk fields, and consequently may be the first direct signature of the model. Four-dimensional general covariance completely determines the couplings of the modulus to Standard Model fields. The strength of these couplings is determined by a single parameter which is set by the TeV rather than the Planck scale.