Searcharxiv⌕ Search

arXiv subjects

Cosmin Macesanu

Publications and source records attributed to Cosmin Macesanu.

17 recordsLinked to original sources
arXiv2006

Precision electroweak constraints on Universal Extra Dimensions revisited

We reconsider the constraints on Universal Extra Dimensions (UED) models arising from precision electroweak data. We take into account the subleading contributions from new physics (expressed in terms of the X,Y ... variables), as well as two loop corrections to the Standard Model rho parameter. For the case of one extra dimension, we obtain a lower bound on the inverse compactification scale M = R^{-1} of 600 GeV (at 90% confidence level), with a Higgs mass of 115 GeV. However, in contradiction to recent claims, we find that this constraint is significantly relaxed with increasing Higgs mass, allowing for compactification scales as low as 300 GeV. LEP II data does not significantly affect these results.

hep-ph↗
arXiv2006

On Dark Matter Self-Interactions from Higher Dimensional Gravity

It has recently been suggested that in a brane world scenario with large extra dimensions, short distance gravitational interactions can enhance the dark matter scattering cross-section in a velocity dependent way. Such a modification may then help to address possible problems with non-interacting cold dark matter on galactic and sub-galactic scales. We argue that, considering the singular character of the higher dimensional Newtonian potential, the scattering cross-section is UV-dependent, depending ultimately on the underlying quantum gravity theory considered. We demonstrate that for a wide class of unitary short distance regularizations, the actual cross-section is velocity-independent and does not significantly affect dark matter substructure. We comment on the problem of thermalization of ultra-light cold dark matter by gravitational interactions in the early universe.

astro-ph↗
arXiv2005

The Phenomenology of Universal Extra Dimensions at Hadron Colliders

Theories with extra dimensions of inverse TeV size (or larger) predict a multitude of signals which can be searched for at present and future colliders. In this paper, we review the different phenomenological signatures of a particular class of models, universal extra dimensions, where all matter fields propagate in the bulk. Such models have interesting features, in particular Kaluza-Klein (KK) number conservation, which makes their phenomenology similar to that of supersymmetric theories. Thus, KK excitations of matter are produced in pairs, and decay to a lightest KK particle (LKP), which is stable and weakly interacting, and therefore will appear as missing energy in the detector (similar to a neutralino LSP). Adding gravitational interactions which can break KK number conservation greatly expands the class of possible signatures. Thus, if gravity is the primary cause for the decay of KK excitations of matter, the experimental signals at hadron colliders will be jets + missing energy, which is typical of supergravity models. If the KK quarks and gluons decay first to the LKP, which then decays gravitationally, the experimental signal will be photons and/or leptons (with some jets), which resembles the phenomenology of gauge mediated supersymmetry breaking models.

hep-ph↗
arXiv2005

Neutrino Masses and Mixings in a Minimal SO(10) Model

We consider a minimal formulation of SO(10) Grand Unified Theory wherein all the fermion masses arise from Yukawa couplings involving one 126 and one 10 of Higgs multiplets. It has recently been recognized that such theories can explain, via the type-II seesaw mechanism, the large ν_μ- ν_τmixing as a consequence of b-tau unification at the GUT scale. In this picture, however, the CKM phase δlies preferentially in the second quadrant, in contradiction with experimental measurements. We revisit this minimal model and show that the conventional type-I seesaw mechanism generates phenomenologically viable neutrino masses and mixings, while being consistent with CKM CP violation. We also present improved fits in the type-II seesaw scenario and suggest fully consistent fits in a mixed scenario.

hep-ph↗
arXiv2005

The Higgs Sector on a Two-Sheeted Space Time

We present a general formalism based on the framework of non-commutative geometry, suitable to the study the standard model of electroweak interactions, as well as that of more general gauge theories. Left- and right-handed chiral fields are assigned to two different sheets of space-time (a discretized version of Kaluza-Klein theory). Scalar Higgs fields find themselves treated on the same footing as the gauge fields, resulting in spontaneous symmetry breaking in a natural and predictable way. We first apply the formalism to the Standard Model, where one can predict the Higgs mass and the top Yukawa coupling. We then study the left-right symmetric model, where we show that this framework imposes constraints on the type and coefficients of terms appearing in the Higgs potential.

hep-ph↗
arXiv2004

Relaxing Cosmological Constraints on Large Extra Dimensions

We reconsider cosmological constraints on extra dimension theories from the excess production of Kaluza-Klein gravitons. We point out that, if the normalcy temperature is above 1 GeV, then graviton states produced at this temperature will decay early enough that they do not affect the present day dark matter density, or the diffuse gamma ray background. We rederive the relevant cosmological constraints for this scenario.

hep-ph↗
arXiv2004

Single Kaluza Klein Production in Universal Extra Dimensions

In the universal extra dimensions models, Kaluza Klein excitations of matter are generaly produced in pairs. However, if matter lives on a fat brane embedded in a larger space, gravity-matter interactions do not obey KK number conservation, thus making possible the production of single KK excitations at colliders. We evaluate the production rates for such excitations at the Tevatron and LHC colliders, and look for ways to detect them.

hep-ph↗
arXiv2001

QCD Loop Corrections to Top Production and Decay at e^+ e^- Colliders

We present a computation of QCD next-to-leading order virtual corrections to the top production and decay process at linear colliders. The top quarks are allowed to be off-shell and the production and decay subprocesses are treated together, thus allowing for interference effects. The framework employed for our computation is the double pole approximation (DPA). We describe the implementation of this approximation for the top production and decay process and compare it with the implementation of DPA for the evaluation of QED corrections to the W pair production at LEP II. Similarities and differences between the two cases are pointed out. One result of interest is the incomplete cancelation of interference corrections. Other results include values for the total NLO top production cross section, and the impact the nonfactorizable (interference) corrections have on the top invariant mass distribution.

hep-ph↗
arXiv2001

The Top Quark at Linear Colliders: QCD Corrections

We present a computation of QCD next-to-leading order corrections to the top production and decay process at linear colliders. The top quarks are allowed to be off-shell and the production and decay subprocesses are treated together, thus allowing for interference effects. Real gluon radiation effects as well as virtual corrections are evaluated. The framework employed for this computation is the double pole approximation (DPA).The results discussed include studies of the gluon radiation properties, interference between production- and decay- stage radiation, and top mass reconstruction.

hep-ph↗
arXiv2000

Gluon Radiation in Top Quark Production and Decay at $e^+e^-$ Colliders

We study gluon radiation in top quark production above threshold at high energy $e^+e^-$ colliders. We allow for the top quarks to be off-shell, considering radiation in both the top production and decay processes simultaneously. Our calculation includes all top width effects, spin correlations, and $b$ quark mass effects. We study the effects of gluon radiation on top mass reconstuction and examine the interference between production- and decay-stage radiation, which can be sensitive to the value of the top quark decay width.

hep-ph↗
arXiv2000

Top Production and Decay at Linear Colliders: QCD Corrections

We present the results of an exact calculation of gluon radiation in top production and decay at high energy electron-positron colliders. We include all spin correlations and interferences, the bottom quark mass, and finite top width effects in the matrix element calculation. We study properties of the radiated gluons and implications for top mass measurement. We also discuss virtual corrections to the process.

hep-ph↗
arXiv2000

QCD Loop Corrections to Top Production and Decay

We discuss the computation of QCD virtual corrections to the top production and decay process at linear colliders. The double pole approximation (DPA) is used, and we comment on similarities and differences between our results and results obtained in a similar framework for the QED corrections to the W pair production process at LEPII.

hep-ph↗
arXiv2000

Gluon Radiation in Top Production and Decay

We present the results of an exact calculation of gluon radiation in top production and decay at high energy electron-positron colliders. We include all spin correlations and interferences, the bottom quark mass, and finite top width effects in the matrix element calculation. We study properties of the radiated gluons and implications for top mass measurement.

hep-ph↗
arXiv1999

Top and gluons at lepton colliders

In this talk we present results of an exact calculation of gluon radiation in top production and decay at lepton colliders, including all spin correlations and interferences. We compare properties of gluons radiated in the production and decay stages and investigate the sensitivity of interference effects to the top decay width.

hep-ph↗
arXiv1998

Could the $τ$ be substantially different from $e$ and $μ$ in the supersymmetric standard model?

R-parity stands as an ad hoc assumption in the most popular version of the supersymmetric standard model. More than fifteen years' studies of R-parity violations have been restricted to various limiting scenarios. We illustrate how the single-VEV parametrization provides a workable framework to analyze the phenomenology of the complete theory of supersymmetry without R-parity. In our comprehensive study of various aspects of the resulting leptonic phenomenology at tree-level, we find that the physical $τ$ lepton could actually bear substantial gaugino and higgsino components, making it very different from the $e$ and the $μ$.

hep-ph↗
arXiv1998

A Simple Phenomenological Parametrization of Supersymmetry without R-Parity

We present a parametrization of the supersymmetric standard model without R-parity that permits efficient phenomenological analyses of the full model without a priori assumptions. Under the parametrization, which is characterized by a single vacuum expectation value for the scalar components of the Y=-1/2 superfields, the expressions for tree-level mass matrices are quite simple. They do not involve the trilinear R-parity violating couplings; however, the bilinear μ_i terms do enter and cannot be set to zero without additional assumptions. We set up a framework for doing phenomenology and show some illustrative results for fermion mass matrices and related bounds on parameters. We find in particular that large values of tan(beta) can suppress R-parity violating effects, substantially weakening experimental constraints.

hep-ph↗