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Register a new userDeuteron electric dipole moment from holographic QCD
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We compute the electric dipole moment (EDM) of the deuteron in the holographic QCD model of Witten-Sakai-Sugimoto. Previously, the leading contribution to the EDM of nucleons was computed, finding opposite values for the proton and the neutron which then cancel each other in the deuteron state. Here we compute the next-to-leading order contribution which provides a splitting between their absolute value. At large $N_{rm c}$ and large t Hooft coupling $lambda$, nuclei are bound states of almost isolated nucleons. In particular, we find that in this limit the deuteron EDM is given by the splitting between proton and neutron EDMs. Our estimate for the deuteron EDM extrapolated to the physical values of $N_{rm c}$, $lambda$, $M_{rm KK}$ and $m_q$ is $mathcal{D}_D = -0.92times 10^{-16} theta e cdot {cm}$. This is consistent, in sign and magnitude, with results found previously in the literature and obtained using completely different methods.
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The connection between a regularization-independent symmetric momentum substraction (RI-$tilde{rm S}$MOM) and the $overline{rm MS}$ scheme for the quark chromo EDM operators is discussed. A method for evaluating the neutron EDM from quark chromoEDM is described. A preliminary study of the signal in the matrix element using clover quarks on a highly improved staggered quark (HISQ) ensemble is shown.
In this paper, the renormalization-group equations for the (flavor-conserving) CP-violating interaction are derived up to the dimension six, including all the four-quark operators, at one-loop level. We apply them to the models with the neutral scalar boson or the color-octet scalar boson which have CP-violating Yukawa interactions with quarks, and discuss the neutron electric dipole moment in these models.
We compute the electric dipole moment of nucleons in the large $N_c$ QCD model by Witten, Sakai and Sugimoto with $N_f=2$ degenerate massive flavors. Baryons in the model are instantonic solitons of an effective five-dimensional action describing the whole tower of mesonic fields. We find that the dipole electromagnetic form factor of the nucleons, induced by a finite topological $theta$ angle, exhibits complete vector meson dominance. We are able to evaluate the contribution of each vector meson to the final result - a small number of modes are relevant to obtain an accurate estimate. Extrapolating the model parameters to real QCD data, the neutron electric dipole moment is evaluated to be $d_n = 1.8 cdot 10^{-16}, theta;ecdot mathrm{cm}$. The electric dipole moment of the proton is exactly the opposite.
The outstanding progress has been made in reducing the upper bounds on EDM of several particles. Even if significant challenges must be overcome to further improve these limits, it is still one of the best chances to detect new type of interactions beyond the standard model. Analyzing several examples, we highlight a common thread that is visible in different set-ups used for the EDM detection. The electric dipole moment is one of the clear consequences of CP- or T-violating interactions, however it is not the only one. These symmetry-violating interactions enable extra phenomena that unavoidably accompany the EDM-induced spin precession, and they must be taken into account in planning and executing sensitive experiments. After reviewing three typical cases, we suggest conditions for improving the sensitivity of detecting the intrinsic EDM.
We extract the neutron electric dipole moment $vert vec{d}_Nvert$ within the lattice QCD formalism. We analyse one ensemble of $N_f=2+1+1$ twisted mass clover-improved fermions with lattice spacing of $a simeq 0.08 {rm fm}$ and physical values of the quark masses corresponding to a pion mass $m_{pi} simeq 139 {rm MeV}$. The neutron electric dipole moment is extracted by computing the $CP$-odd electromagnetic form factor $F_3(Q^2 to 0)$ through small $theta$-expansion of the action. This approach requires the calculation of the topological charge for which we employ a fermionic definition by means of spectral projectors while we also provide a comparison with the gluonic definition accompanied by the gradient flow. We show that using the topological charge from spectral projectors leads to absolute errors that are more than two times smaller than those provided when the field theoretic definition is employed. We find a value of $vert vec{d}_Nvert = 0.0009(24) theta e cdot {rm fm}$ when using the fermionic definition, which is statistically consistent with zero.
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