Fermionic Kaluza-Klein modes in the string-cigar braneworld

Abstract

We study the spin 1/2 and spin 3/2 fermion fields in a thick braneworld scenario in six dimensions called string-cigar model. This smooth string-like model has a source that satisfies the dominant energy condition and undergoes a Ricci flow. We propose a new coupling for the fermions with a background gauge field which allows a smooth and normalized massless mode in the brane with positive tension. By numerical methods the mass spectrum and the massive eigenfunctions are obtained. The Kaluza-Klein massive tower exhibits the usual increasing pattern and, in this scenario, the coupling term does not allow tachyonic Kaluza-Klein states. The brane core and the background gauge field alter the properties of the massive KK tower, enhancing the amplitude of the massive states near the origin and changing the properties of the analogue Schroedinger potential. Furthermore, we find massive modes as resonant states in this scenario for both fermionic fields.Comment: Final version to appear in Physical Review D. Section II substantially enlarged in order to do a comprehensive review of the thin string brane model and string cigar brane model. One section added for considering of the Rarita-Schwinger spinor field. Some references added. 35 pgs, 17 fig

Exotic Elko on string-like defects in six dimensions

“…This geometry is built upon a warped product between a 3-brane and the cigar soliton space, which is a 2D stationary solution for the Ricci flow [12][13][14]. Moreover, the changes performed by this regular HC model in comparison to the non-regular GS model arise just close to the origin.…”

“…In order to solve some issues involving the regularity and energy conditions, we use in this paper the regular thick model so-called Hamilton string-cigar (HC) [12][13][14]:…”

“…We demonstrate in this paper that the complex-valued Elko massive eigenfunctions can be removed by a covariant derivative specific coupling. In fact, regarding spin 1/2 Dirac (or Weyl) fermions and spin 3/2 Rarita-Schwinger fermions in 6D models, minimal couplings with an electromagnetic vector U (1) gauge background field are performed in order to bound the zero mode [14,21,42,43]. However, since Elko is a dark spinor, there is no interaction with electromagnetic gauge field, but an exotic spin structure term (such as 1-form field representing an element of the cohomology group H 1 (M, Z 2 )) is allowed though [44][45][46][47][48].…”

“…Moreover, in order to remove the Elko massive complex-valued eigenfunction, we introduce a 4D exotic coupling of Elko spinor fields [44,45], which also prevents the existence of bounded massive modes. To this end, we made a brief review of string-like defects, using the Gergheta-Shaposhnikov (GS) thin model [11,16,21] and the Hamilton string-cigar thick model (HC) [12][13][14]. Next, we show the task of the Elko spinor confinement in string-like models.…”

“…This paper focus on six-dimensional (6D) anti-de Sitter (AdS 6 ) brane-worlds, which have some interesting features. In fact, the mass hierarchy is solved without any requirement of fine tuning between the bulk cosmological constant and the brane tension [11], with correction O(d −3 ) to the Newtonian potential [11][12][13][14][15] that is smaller than within five-dimensional (5D) models [2]. Moreover, 6D models support the localisation of free gauge zero modes, even in the thin brane case [16][17][18], whereas a scalar coupling in the AdS 5 case is demanded [4].…”