Mon·Jan 16, 2017Monday·January 16, 2017

1. 01*

   Revisiting fine-tuning in the MSSM

   Graham G. Ross🇬🇧 · Kai Schmidt-Hoberg🇩🇪 · Florian Staub🇩🇪

   We evaluate the amount of fine-tuning in constrained versions of the minimal supersymmetric standard model (MSSM), with different boundary conditions at the GUT scale. Specifically we study the fully constrained version as well as the cases of non-universal Higgs and gaugino masses. We allow for the presence of additional non-holomorphic soft-terms which we show further relax the fine-tuning. Of particular importance is the possibility of a Higgsino mass term and we discuss possible origins for such a term in UV complete models. We point out that loop corrections typically lead to a reduction in the fine-tuning by a factor of about two compared to the estimate at tree-level, which has been overlooked in many recent works. Taking these loop corrections into account, we discuss the impact of current limits from SUSY searches and dark matter on the fine-tuning. Contrary to common lore, we find that the MSSM fine-tuning can be as small as 10 while remaining consistent with all experimental constraints. If, in addition, the dark matter abundance is fully explained by the neutralino LSP, the fine-tuning can still be as low as $\sim$ 20 in the presence of additional non-holomorphic soft-terms. We also discuss future prospects of these models and find that the MSSM will remain natural even in the case of a non-discovery in the foreseeable future.

   hep-phhep-exJHEP(2017)·66 citations
2. 02*

   Mesonic and nucleon fluctuation effects at finite baryon density

   G. Fejos🇯🇵 · A. Hosaka🇯🇵

   Mesonic and nucleon fluctuation effects are investigated in medium. We couple the nucleon field to the $2+1$ flavor meson model and investigate the finite temperature and density behavior of the system, in particular, the axial anomaly function. Somewhat contrary to earlier expectations we find that it tends to strengthen at finite density. At lower temperatures nucleon density fluctuations can cause a relative difference in the $U_A(1)$ axial anomaly of about $20\%$. This has important consequences on the mesonic spectra, especially on the $\eta -{\eta }^{\prime }$ system, as we observe no drop in the ${\eta }^{\prime }$ mass as a function of the baryochemical potential, irrespective of the temperature. Based on the details of chiral symmetry restoration, it is argued that there has to be a competition between underlying QCD effects of the anomaly and fluctuations of the low energy hadronic degrees of freedom, and the fate of the $U_A(1)$ coefficient should be decided by taking into account both effects simultaneously.

   hep-phnucl-thPRD(2017)·15 citations
3. 03*

   Nucleon resonances $N(1875)$ and $N(2100)$ as strange partners of LHCb pentaquarks

   Jun He🇨🇳

   In this work, we investigate the possibility of interpreting two nucleon resonances, the $N(1875)$ and the $N(2100)$, as hadronic molecular states from the ${\Sigma }^{\ast }K$ and $\Sigma K^{\ast }$ interactions, respectively. With the help of effective Lagrangians in which coupling constants are determined by the SU(3) symmetry, the ${\Sigma }^{\ast }K$ and $\Sigma K^{\ast }$ interactions are described by the vector-meson and pseudoscalar-meson exchanges. With the one-boson-exchange potential obtained, bound states from the ${\Sigma }^{\ast }K$ and $\Sigma K^{\ast }$ interactions are searched for in a quasipotential Bethe-Saltpeter equation approach. A bound state with quantum number $I(J^P)=1/2(3/2^{-})$ is produced from the ${\Sigma }^{\ast }K$ interaction, which can be identified as the $N(1875)$ listed in PDG. It can be seen as a strange partner of the LHCb pentaquark $P_c(4380)$ with the same quantum numbers in the molecular state picture. The $\Sigma K^{\ast }$ interaction also produces a bound state with quantum number $I(J^P)=1/2(3/2^{-})$, which is related to experimentally observed $N(2100)$ in the $\varphi$ photoproduction. Our results suggest that the $N(2120)$ observed in the $K\Lambda (1520)$ photoproduction and the $N(2100)$ observed in the $\varphi$ photoproduction have different origins. The former is a conventional three-quark state while the latter is a $\Sigma K^{\ast }$ molecular state, which can be seen as a strange partner of the $P_c(4450)$ with different spin parity.

   hep-phhep-exnucl-exnucl-thPRD(2017)·69 citations
4. 04*

   Pseudomagnetic effects for resonance neutrons in the search for time reversal invariance violation

   Vladimir Gudkov🇺🇸 · Hirohiko M. Shimizu🇯🇵

   A general theory of pseudomagnetic effects for the propagation of polarized neutrons through polarized target in multi resonance approach is presented. Some applications related to the proposed search for time reversal invariance violation in neutron scattering are considered.

   ↳ nucl-thhep-phPRC(2017)·9 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.