# Naturalness in D-brane inspired models

Benedetti, Ron (0000 0001 0662 7451, grid.64337.35, Department of Chemistry and Physics, Louisiana State University, Shreveport, LA, 71115, U.S.A.) ; Li, Tianjun (0000000119573309, grid.9227.e, CAS Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing, 100190, P.R. China) (0000 0004 1797 8419, grid.410726.6, School of Physical Sciences, University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing, 100049, P.R. China) ; Maxin, James (0000 0001 0662 7451, grid.64337.35, Department of Chemistry and Physics, Louisiana State University, Shreveport, LA, 71115, U.S.A.) ; Nanopoulos, Dimitri (0000 0004 4687 2082, grid.264756.4, George P. and Cynthia W. Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M; University, College Station, TX, 77843, U.S.A.) (0000 0001 0194 7560, grid.420764.3, Astroparticle Physics Group, Houston Advanced Research Center (HARC), Mitchell Campus, Woodlands, TX, 77381, U.S.A.) (0000 0001 2358 8802, grid.417593.d, Academy of Athens, Division of Natural Sciences, 28 Panepistimiou Avenue, Athens, 10679, Greece)

10 July 2019

Abstract: We examine the naturalness of the D-brane inspired model constructed in flipped SU(5) supplemented with vector-like particles at the TeV scale, dubbed flippons. We find the model can produce a mainly Higgsino-like lightest supersymmetric particle (LSP) and small light stops, as favored by naturalness. In fact, a large trilinear scalar A t term at the electroweak (EW) scale creates a large mass splitting between the top squarks, driving the light stop to near degeneracy with an LSP that is almost all Higgsino, with Δ M t ˜ 1 χ ˜ 1 0 $\Delta M\left({\tilde{t}}_1,{\tilde{\chi}}_1^0\right)$ < 5GeV, evading the LHC constraint on t ˜ 1 → c χ ˜ 1 0 ${\tilde{t}}_1\to c{\tilde{\chi}}_1^0$ thus far. Given the smallness of the light stop, generating a 125 GeV light Higgs boson mass is aided by one-loop contributions from the Yukawa couplings between the flippons and Higgs fields. The resulting parameter space satisfying naturalness is rather constrained, thus we assess its viability by means of comparison to the LHC constraint on soft charm jets and direction detection limits on spin-independent cross-sections. Finally, we compute the level of electroweak fine-tuning and uncover a region with Δ EW < 30, i.e., fine-tuning better than 3%, regarded as low electroweak fine-tuning. Given the small light stop, the electroweak fine-tuning from only the top squarks is of O $\mathcal{O}$ (1), indicating no fine-tuning from neither the light stop t ˜ 1 ${\tilde{t}}_1$ nor the heavy stop t ˜ 2 ${\tilde{t}}_2$ .

Published in: JHEP 1907 (2019) 048 DOI: 10.1007/JHEP07(2019)048
arXiv: 1904.10809