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D. A. Demir

Publications and source records attributed to D. A. Demir.

At least 37 records · Page 2Linked to original sources
arXiv2000

CP conserving constraints on Supersymmetric CP violation in the MSSM

We address the following question. Take the Constrained Minimal Supersymmetric Standard Model (CMSSM) with the two CP violating SUSY phases different from zero, and neglect the bound coming from the electric dipole moment of the neutron (EDM): is it possible to fully account for CP violation in the kaon and B systems using only the SUSY contributions with vanishing CKM phase? We show that the ${BR}(B\to X_{s} γ)$ constraint, though CP conserving, forces a negative answer to the above question. This implies that, even in the regions of the CMSSM where a cancellation of different contributions to the EDM allows for large SUSY phases, it is not possible to exploit the SUSY phases to fully account for observable CP violation. Hence to have sizeable SUSY contributions to CP violation, one needs new flavor structures in the sfermion mass matrices beyond the usual CKM matrix.

hep-ph↗
arXiv1999

Probing the sources of CP violation via B -> K^* l^+ l^- decay

The B -> K^* l^+ l^- (l = mu, tau) is analyzed in a minimally extended Standard Model in which the Wilson coefficients have new CP-odd phases. The sensitivity of the CP asymmetry and lepton polarization asymmetries to the new phases is discussed. It is found that the CP asymmetry is sensitive to the new phase in the Wilson coefficient C_7 whereas the normal lepton polarization asymmetry is sensitive to the phase in the Wilson coefficient C_(10). Additionally, the correlation between the CP and normal lepton polarization asymmetries is studied. A simultaneous measurement of these two asymmetries can be useful in search for the existence of the new sources of CP violation beyond the Standard Model.

hep-ph↗
arXiv1999

Higgs pair production in the MSSM with explicit CP violation

In the minimal supersymmetric standard model with explicit CP violation, associated production of the lightest Higgs boson with heavier ones is analyzed. Due to explicit CP violation, the Higgs bosons are no longer CP eigenstates so that both of the heavy Higgs bosons contribute to the process. While the radiative corrections in the Higgs sector turn out to be quite important, the vertex radiative corrections remain small as in the CP conserving theory.

hep-ph↗
arXiv1999

Fully Supersymmetric CP Violation in K and B Systems

We analyze CP violation in supersymmetric extensions of the Standard Model with heavy scalar fermions of the first two generations. Neglecting intergenerational mixing in the sfemion mass matrices and thus considering only chargino, charged Higgs and W--boson diagrams we show that it is possible to fully account for CP violation in the kaon system even in the absence of the standard CKM phase. This opens new possibilities for large supersymmetric contributions to CP violation in the B system.

hep-ph↗
arXiv1999

Additional phases induced by the supersymmetric CP phases

The explicit CP violation in the MSSM radiatively induces a finite unremovable alignment between the Higgs doublets. This additinal phase can be as large as the original CP phases in certain portions of the MSSM parameter space. Considering the specific case of the charginos, this additional phase is shown to induce a conceivable amount of CP violation near the would--be CP conserving points. Moreover, the CP violation in the absence of this phase is smaller than the one in the presence of it, and the former can never compete with the latter, however large $\tanβ$ is.

hep-ph↗
arXiv1999

gg\to γ\bar{f}f in the strongly interacting phase of the MSSM

g g \to γ\bar{f}f scattering is discussed in the strongly interacting phase of the MSSM. The rate for the decay h \to γ\bar{f} f is computed in the MSSM and SM, and values of the Higgs-sfermion coupling needed for the former to dominate on the latter are identified. It is found that the MSSM signal dominates on the SM one for Higgs-sfermion couplings well below the one needed for developing stopponium bound states via Higgs mediation.

hep-ph↗
arXiv1999

Probing the phases in the MSSM via e^+ e^- \to h A

In the presence of the supersymmetric CP phases, e^+ e^- \to Z^{*} \to h A scattering is analyzed, with special emphasis on Z^{*} h A vertex, taking into account radiatve corrections due to dominant top quark and top squark loops in the Higgs sector as well as the vertex formfactors. It is found that the lightest Higgs remains essentially CP-even whereas the heavier ones mix with each other strongly. Moreover, the supersymmetric CP phases are found to create tree-level couplings between a pseudoscalar and identical sfermion mass eigenstates which, together with the radiative corrections in the Higgs sector, are found to enhance the vertex formfactors significantly.

hep-ph↗
arXiv1999

Effects of the supersymmetric phases on the neutral Higgs sector

By using the effective potential approximation and taking into account the dominant top quark and scalar top quark loops, radiative corrections to MSSM Higgs potential are computed in the presence of the supersymmetric CP-violating phases. It is found that, the lightest Higgs scalar remains essentially CP-even as in the CP-invariant theory whereas the other two scalars are heavy and do not have definite CP properties. The supersymmetric CP-violating phases are shown to modify significantly the decay rates of the scalars to fermion pairs.

hep-ph↗
arXiv1999

Implications of Δρand CHARM II data for Z' Physics

We discuss the constraints on the Z' model parameters coming from Z- pole and low-energy ν_μ-e scattering data in the frame work of GUT- motivated models. We find that when the coupling constant of the extra U(1) is small (large) the parameter space is mainly determined by the Z-pole (the low-energy ν_μ-e scattering) data.

hep-ph↗
arXiv1999

Real-time tunneling

Starting with the equivalence of the rest energy of a particle to an amount of the radiant energy characterized by a frequency, in addition to the usual relativistic transformation rules leading to the wave-particle duality, we investigate the case in which this frequency is an internal propery of the particle. This kind of interpretation of the frequency is shown to be relevant to the tunneling effect. The investigations in this direction yield (1) a purely real time everywhere, (2) an anti-hermitian momentum operator, (3) a corpuscular structure for the particle, and (4) all of the known theoretical predictions about the tunneling effect.

quant-ph↗
arXiv1998

Weak-scale hidden sector and electroweak Q-balls

By extending the scalar sector of the Standard Model (SM) by a U(1) singlet, we show that the electroweak symmetry breaking enables the formation of a stable, electrically neutral, colorless Q-ball which couples to the SM particle spectrum solely through the Higgs boson. This Q-ball has mainly weak and gravitational interactions, and behaves as a collection of weakly interacting massive particles. Therefore, it can be a candidate for the dark matter in the universe.

hep-ph↗
arXiv1998

e^+e^-\to (h A)\to bbbb in Abelian Extended Supersymmetric Standard Model

We discuss the $e^{+}e^{-}\to (h A)\to bbbb$ cross section in an Abelian extended SM. We work in that minimum of the scalar potential for which Higgs trilier coupling is greater than the soft mass parameters. We find that nex-to-lightest Higgs gives the essential contribution to the cross section in the small $Z-Z'$ mixing angle and leptophobic $Z'$ limit.

hep-ph↗
arXiv1998

Higgs-strahlung in Abelian Extended Supersymmetric Standard Model

We analyze the Higgs production via the Higgs-strahlung process $e^{+}e^{-}\to h_{k}{\it{l}}^{+}{\it{l}}^{-}$ in an Abelian Extended Supersymmetric SM. We work in the large Higgs trilinear coupling driven minimum of the potential, and find that the next-to-lightest Higgs cannot be produced by this process. Other Higgs scalars, namely the lightest and the heaviest, have cross sections comparable to that in the pure SM. It is found that the present model has observable differences with the other popular model, NMSSM, in the same type of minimum.

hep-ph↗
arXiv1998

One-Loop Effects in Supergravity Models with an Additional U(1)

For an Abelian extended Supergravity model, we investigate some important low energy parameters: \tanβ, Z-Z' mixing angle, lightest CP-even Higgs mass bound, Z' mass, and effective μparameter. By integrating the RGE's from string scale down to the weak scale we constuct the scalar potential, and analyze the quantities above at the tree- and one-loop levels by including the contributions of top squarks and top quark in the effective potential. PACS: 04.65.+e, 12.60.Jv

hep-ph↗
arXiv1998

Two-Higgs doublet models from TeV-scale supersymmetric extra U(1) models

We investigate the reduction of a general TeV-scale supersymmetric extra U(1) model to a 2HDM below the TeV- scale through the tree level non-decoupling. Portions of the parameter space of the extra U(1) model appropriate for obtaining a 2HDM are identified. Various properties of the resulting 2HDM are connected to the parameter space of the underlying model. PACS: 12.60.Jv, 12.60.Cn, 12.60.Fr

hep-ph↗
arXiv1998

Electroweak Breaking and the mu problem in Supergravity Models with an Additional U(1)

We consider electroweak symmetry breaking in supersymmetric models with an extra non-anomalous U(1)' gauge symmetry and an extra standard-model singlet scalar S. For appropriate charges the U(1)' forbids an elementary mu term, but an effective mu is generated by the VEV of S, leading to a natural solution to the mu problem. There are a variety of scenarios leading to acceptably small Z-Z' mixing and other phenomenological consequences, all of which involve some but not excessive fine tuning. One class, driven by a large trilinear soft supersymmetry breaking term, implies small mixing, a light Z' (e.g., 200 GeV), and an electroweak phase transition that may be first order at tree level. In another class, with m_S^2 < 0 (radiative breaking), the typical scale of dimensional parameters, including M_{Z'} and the effective mu, is O(1 TeV), but the electroweak scale is smaller due to cancellations. We relate the soft supersymmetry breaking parameters at the electroweak scale to those at the string scale, choosing Yukawa couplings as determined within a class of string models. We find that one does not obtain either scenario for universal soft supersymmetry breaking mass parameters at the string scale and no exotic multiplets contributing to the renormalization group equations. However, either scenario is possible when the assumption of universal soft breaking is relaxed. Radiative breaking can also be generated by exotics, which are expected in most string models.

hep-ph↗