Volume 57, Number 56, 2012
Papers presented at the Fourth Southeastern European Workshop
Particle Physics from TeV to Planck Scale  BW2011
Donji Milanovac, Serbia, 28 August  1 September 2011
Guest Editors:
Luis AlvarezGaume
Goran Djordjevic
Goran Senjanovic
Mihai Visinescu
Theoretical Physics
P r e f a c e
Romanian Journal of Physics 57,
783784 (2012)
Black Holes and Other Solutions in Commutative and Noncommutative Gauge Theory of Gravitation Simona Babeţi (Pretorian) Romanian Journal of Physics 57,
785792 (2012)
An analytical procedure conceived in GRTensorII for Maple was developed in order to obtain the leading noncommutative correction based on particular ansatz for gauge fields and noncommutative parameter. Using recursion relations in the noncommutative parameter, the gauge potentials and the components of deformed metric are calculated to second order. The procedure is used for black holes solutions starting with the commutative gauge theory of gravitation and mapping these in a noncommutative theory.
Supersymmetric Dark Energy Neven Bilić Romanian Journal of Physics 57,
793802 (2012)
We study a noninteracting supersymmetric model in de Sitter spacetime. A soft supersymmetry breaking induces a nonzero vacuum energy density. A short distance cutoff of the order of Planck length provides a matching between the vacuum energy density and the cosmological constant related to the de Sitter expansion parameter.
Mass Formulas for SingleCharm Tetraquarks with FermiBreit Hyperfine Interaction V. Borka Jovanović, D. Borka Romanian Journal of Physics 57,
803815 (2012)
In this paper we present the main results of our investigation of the $cq\bar{q}\bar{q}$ singlecharm scalar tetraquarks and their SU(3)_{F} representations: $\overline{15}_S$, $\bar{3}_S$, $6_A$ and $\bar{3}_A$. We use the FermiBreit interaction Hamiltonian with SU(3) flavor symmetry breaking to determine the masses of the singlecharm tetraquarks. We also discuss mass spectra obtained from meson and baryon mass fits. The mass spectra are very similar to those obtained with GlozmanRiska hyperfine interaction, and they indicate that some of the experimentally detected states may have tetraquark nature.
Noncommutativity and TDuality Lj. Davidović, B. Nikolić, B. Sazdović Romanian Journal of Physics 57,
816829 (2012)
We will discuss the relation between the open string parameters $G^{eff}_{\mu\nu}(G, B)$ and $\theta^{\mu\nu}(G, B)$ and Tdual background fields $^*G^{\mu\nu}(G, B)$ and $^*B^{\mu\nu}(G, B)$ given in terms of the initial background fields: metric tensor $G_{\mu\nu}$ and KalbRamond field $B_{\mu\nu}$. The investigations are extended to the case of type IIB superstring theory with bosonic and fermionic Tduality as well as to the case of ”weakly curved background”.
Renormalizability of the DDeformed WessZumino Model Marija Dimitrijević, Biljana Nikolić, Voja Radovanović Romanian Journal of Physics 57,
830840 (2012)
We discuss a deformation of superspace which is defined using the twist formalism. The twist we use is nonhermitian and it is given in terms of the covariant derivatives $D_{\alpha}$. We calculate oneloop divergences in the twopoint, threepoint and fourpoint Green functions. Possibilities to render the model renormalizable are discussed.
Slow Roll Inflation: A Somehow Different Perspective Cristiano Germani Romanian Journal of Physics 57,
841848 (2012)
In this note we point out that, contrary to the standard point of view, slow roll inflation is due to high gravitational friction. We show that the requirement of slow roll coincides with the requirement of a flat scalar field potential in the case of minimally coupled scalar field. In this sense, the search for a successful inflationary theory may be more fruitful by shifting the focus on models with high gravitational friction. We review then a gravitational mechanism, the so called ”Gravitationally Enhanced Friction” mechanism, such that high gravitational friction is dynamically generated during inflation allowing even steep (i.e. nonflat) scalar potential to inflate.
FourDimensional Nernst Branes M. Haack Romanian Journal of Physics 57,
849856 (2012)
This is a short summary of the results of [1], as presented at the BW2011 Workshop. Compared to the original paper it contains some additional pedagogical background information, following the talk at the workshop.
1. S. Barisch, G. L. Cardoso, M. Haack, S. Nampuri and N. A. Obers, JHEP 1111, 090 (2011) [arXiv:1108.0296/hepth].
SParameter Estimation for Walking Technicolor by a New Version of the ACD Method Siniša R. Ignjatović Romanian Journal of Physics 57,
857862 (2012)
The PeskinTakeuchi Sparameter is sensitive to physics beyond the Standard Model. The current experimental data favor the Standard Model value $S = 0$. The Walking Technicolor (WTC) is a model of dynamical electroweak symmetry breaking with a very slowly running (walking) coupling constant, which makes its dynamics different from QCD. While Technicolor models tend to yield $S > 0$, WTC helps reduce this value. An early evaluation of the Sparameter for WTC (S_{WTC}) used the unreliable Analytic Continuation by Duality (ACD) method. ACD is used to evaluate dispersive integrals using largemomentum expansion of the vacuum polarization, usually the first few terms of the Operator Product Expansion (OPE). The original ACD method depends on the approximation of $1/s$ by polynomials and is unstable while a simplified version is stable, but gives only a lower bound for S_{WTC}. A new version of the ACD matches the polynomial to $1/s$ at the peaks of dominant resonances in the vector and axial channels. S_{WTC} is expressed in terms of 1) two unknown (due to uncertainties in the OPE for WTC) parameters – by far the greatest source of the uncertainties, and 2) ratios of the masses of the resonances, also unknown for WTC. The WTC dynamics necessitates addition of at least one additional resonance. Negative SWTC is obtained in many cases. It is possible to obtain $S = 0$ in several ways, e.g. if the parameters derived from OPE coefficients for WTC are small and the resonances in WTC spectrum are spaced further apart compared to the lowenergy QCD spectrum.
A Precise Determination of the Expansion History of the Universe Up to z ~ 2 Raul Jimenez Romanian Journal of Physics 57,
863872 (2012)
I present some recent results on efforts to constraint the variation of dark energy as a function of redshift. In particular I concentrate on observational determinations of the expansion history $H(z)$. I also review a formalism that constructs an effective theory of accelerated expansion with a well defined cutoff. This in turn allows to construct the Lagrangian of accelerated expansion. This is done in this paper. I show how the shape of the dark energy potential can be recovered non parametrically using this formalism. This reconstruction can also be used in other approaches followed in the literature (e.g., the reconstruction of the redshift evolution of the dark energy equation of state w(z)). Using observations of passively evolving galaxies I derive constraints on the dark energy potential shape in the redshift range $0.1 < z < 1.8$. It is shown that at the $1\sigma$ level the potential is consistent with being constant at the few % level. This is the first time that such accuracy has been achieved, opening the possibility to unveil the symmetries underlying accelerated expansion.
Recent Observational Challenges to Dark Matter Paradigm P. Jovanović Romanian Journal of Physics 57,
873878 (2012)
Here we study some possible consequences of recently observed TullyFisher relation for gas rich galaxies, as well as perturbed stellar motions around the black hole in Galactic center on dark matter paradigm. We investigate the ability of some alternative approaches which require modifications of fundamental gravitational and/or dynamical laws to explain these observational results. We found that predictions of modified Newtonian dynamics for orbital precession of S2 star strongly depend on the choice of interpolating function, which in turn could also affect its predictions regarding TullyFisher relation. On the other hand, $R^n$ gravity causes retrograde precession of pericenter of S2 star (which is opposite to the predictions of General Relativity), and hence could reproduce the effects of extended dark matter distributed inside its orbit.
Footprints of HigherDimensional Decaying Black Holes Panagiota Kanti Romanian Journal of Physics 57,
879893 (2012)
We review the current results for the emission of Hawking radiation by a higher dimensional black hole during the Schwarzschild and the spindown phases. We discuss particularly the role of the angular variation of the emitted radiation on the brane during the latter phase, the radiation spectra for gravitons in the bulk, and the effect of the mass of the emitted particles in determining the bulktobrane energy balance.
Modified NonLocal Gravity Alexey S. Koshelev Romanian Journal of Physics 57,
894900 (2012)
In this note I provide an extended version of the talk given at BW2011 workshop. The concise introduction to the nonlocal SFT motivated models is given with an emphasis on the nonlocal generalization of gravity. A number of open questions and future directions in the development of such models is outlined.
Invisible Higgs and Scalar Dark Matter Yann Mambrini Romanian Journal of Physics 57,
901905 (2012)
In this proceeding, we show that when we combined WMAP and the most recent results of XENON100, the invisible width of the Higgs to scalar dark matter is negligible ($\lesssim 10 \%$), except in a small region with very light dark matter ($\lesssim 10$ GeV) not yet excluded by XENON100 or around 60 GeV where the ratio can reach 50% to 60%. The new results released by the Higgs searches of ATLAS and CMS set very strong limits on the elastic scattering cross section.
FTheory Compactifications on Manifolds with SU(3) Structure Andrei Micu Romanian Journal of Physics 57,
906915 (2012)
In this paper we derive part of the low energy action corresponding to Ftheory compactifications on specific eight manifolds with SU(3) structure. The setup we use can actually be reduced to compactification of sixdimensional supergravity coupled to tensor multiplets on a $T^2$ with duality twists. The resulting theory is a $N = 2$ gauged supergravity coupled to vectortensor multiplets.
On Description of Black Hole Motion in Entropic Reformulation of General Relativity A.Morozov Romanian Journal of Physics 57,
916923 (2012)
A naive attempt is made to deduce classical equations of motion of two interacting black holes from entropic principle, identifying the action with a sum of horizon areas. These areas depend on accelerations of the black holes and on distance between them. Attempt is only partly successful: the two numeric coefficients, parameterizing the deviation from Newton’s second and gravitational laws coincide, but are different from unity.
Neutrino Mass and the LHC M. Nemevšek Romanian Journal of Physics 57,
924930 (2012)
We discuss the feasibility of probing the physics of neutrino mass generation at the LHC and its connection to low energy phenomena. Motivation for existence of a low scale of the neutrino mass operator might be provided by an observation of a signal in neutrinoless beta decay searches, which may run in tension with cosmology, if neutrino mass is its only source. An example of a theory which resolves this tension, and at the same time may be probed at the LHC, is provided by the minimal leftright (LR) symmetric model with Majorana neutrinos. We show how colliders can probe lepton number and flavor violating couplings and how these are connected to other low energy processes. Moreover, we exemplify the impact of the low luminosity data from the 7 TeV LHC run on the parameter space of the theory, both for the heavy righthanded neutrinos and for doubly charged scalars.
Supersymmetry of Noncommutativity Relations B. Nikolić, B. Sazdović Romanian Journal of Physics 57,
931937 (2012)
In the present paper we investigate the noncommutativity of type IIB superstring theory in pure spinor formulation (up to the quadratic terms) using canonical approach. Boundary conditions, Neumann ones for bosonic coordinates and fermionic boundary conditions preserving half of the initial supersymmetry, are treated as canonical constraints. Solving the constraints we obtain original coordinates in terms of the effective coordinates and momenta. We show that noncommutativity relations are consistent with $N = 1$ supersymmetry transformations.
Thermal Duality and NonSingular Superstring Cosmology Hervé Partouche Romanian Journal of Physics 57,
938949 (2012)
We review the construction of superconformal field theories on the worldsheet, which describe superstring models where only a finite number of states are effectively thermalized. Compared to conventional superstring models at finite temperature, they are obtained by switching on suitable Wilson lines along the Euclidean time circle $S^1(R_0 )$. This discrete deformation forbids the appearance of tachyons at any radius $R_0$ and restores a Tduality symmetry on the temporal cycle. This implies the existence of a maximal temperature $T_c$, which is equal to twice the standard Hagedorn temperature. The models obtained this way differ substantially from the usual thermal ones only in the regime where the temperature is of order of the string scale, when the canonical ensemble of the full superstring spectrum breaks down. In the tachyon free models, a transition occurs at the temperature $T_c$, which transforms a phase of pure KaluzaKlein excitations along $S^1(R_0)$ into a Tdual phase of pure winding modes. Thanks to the consistency of these thermal backgrounds, cosmological evolutions induced by the free energy are found in various dimensions, with neither Hagedorn instabilities nor initial singularities. They describe bouncing universes, which can be described consistently in perturbation theory throughout the evolution.
Topological Quintessence: Generalizing ΛCDM with Inhomogeneous Dark Energy L. Perivolaropoulos Romanian Journal of Physics 57,
950968 (2012)
There have been observational hints for anisotropy on large cosmological scales accumulating during the last decade. In this talk I review these hints and discuss a concrete cosmological model that could induce cosmological anisotropy on Hubble scales. The model assumes the existence of a Hubble scale dark energy inhomogeneity. Such an inhomogeneity could be induced for example by a topological defect with a Hubble scale core formed during a recent phase transition. An observer displaced from the center of such spherical inhomogeneity would experience a cosmological anisotropy on various cosmological observations. The observational signatures of such anisotropy are discussed and the corresponding current constraints on the model parameters are derived.
Status of CMS Dark Matter Searches in 2011 Sezen Sekmen Romanian Journal of Physics 57,
969978 (2012)
We present the status of dark matter searches performed by the Compact Muon Solenoid Experiment using 7 TeV pp data collected by the CERN Large Hadron Collider in 2010 and 2011. Majority of the results shown here were obtained using 1.1 fb^{−1} of data. We give highlights from analyses searching for candidates like WIMPs, gravitinos, axinos and TeV scale particles. All observations so far were found to be consistent with the Standard Model predictions. The search results were used for setting exclusion limits on various new physics scenarios.
The Oddly Quiet Universe: How the CMB Challenges Cosmology's Standard Model Glenn D. Starkman, Craig J. Copi, Dragan Huterer, Dominik Schwarz Romanian Journal of Physics 57,
979991 (2012)
This paper is adapted by a talk given by one of us (GDS) at the SEENET2011 meeting in August 2011 on the Serbian bank of the Danube River.
Vanishing Dimensions: Theory and Phenomenology Dejan Stojkovic Romanian Journal of Physics 57,
9921001 (2012)
Lowerdimensionality at higher energies has manifold theoretical advantages as recently pointed out. Moreover, it appears that experimental evidence may already exists for it  a statistically significant planar alignment of events with energies higher than TeV has been observed in some earlier cosmic ray experiments. If this alignment is not a fluke, then the LHC should be able to see effects associated with the dimensional crossover. Further, (2+1)dimensional spacetimes have no gravitational degrees of freedom, and gravity waves cannot be produced in that epoch in the early universe. This places a universal maximum frequency at which primordial gravity waves can propagate, which may be accessible to future gravitational wave detectors such as LISA. In this talk, the theoretical motivation for ”vanishing dimensions” as well as generic experimental and observational signature will be discussed.
KillingYano Tensors of Rank Three and Lax Pair Tensors Anca Visinescu, Mihai Visinescu Romanian Journal of Physics 57,
10021010 (2012)
Higher order first integrals of Hamiltonian systems are investigated and the special role of the Killing tensors is pointed out. A geometrical interpretation of the Lax representation in connection with third rank KillingYano tensors is discussed. Some examples of spacetimes involved in recent studies of higher dimensional black holes admitting KillingYano tensors of rank three are presented.
On Cosmologies with NonMinimally Coupled Scalar Fields, the "reverse Engineering Method" and the Einstein Frame Dumitru N. Vulcanov, Goran S. Djordjevic Romanian Journal of Physics 57,
10111016 (2012)
This article is mainly dedicated to the socalled ”Reverse Engineering Method” (reconstructing the shape of the potential in cosmologies based on a scalar field and starting with the time behavior of the scale factor) recently developed by Ellis and Madsen [1] and other authors [2, 3], this time for a cosmology with a scalar field nonminimally coupled with gravity. It is more convenient to perform a conformal transformation of the metric to the so called Einstein frame [4]. In Einstein frame the new redefined scalar field appears to be only minimally coupled, thus we can proceed with REM as was prescribed by Ellis and Madsen and then transform back the main operators in the normal frame. We processed several examples pointing out the influence of the nonminimal coupling on the evolution of the universe.
1. G. F. R. Ellis and M. S. Madsen, Class. Quantum Grav. 8, pp. 667–676 (1991). 2. D. N. Vulcanov, Central European Journal of Physics 6(1), pp. 84–96 (2008). 3. G. S. Djordjevic, C. A. Sporea, D. N. Vulcanov, On the Reverse Engineering Method in Cosmologies with NonMinimally Coupled Scalar Field, Physics Conference TIM10. AIP Conf. Proc. 1387, pp. 98–103 (2011). 4. S. Tsujikawa, Phys. Rev. D62, p. 043512 and references cited there (2000).
The Backreaction of Localized Sources and de Sitter Vacua Marco Zagermann Romanian Journal of Physics 57,
10171025 (2012)
Dbranes and orientifold planes are important ingredients in semirealistic type II string compactifications. Determining their explicit backreaction on the compactification background poses generically a difficult computational problem. This problem is greatly simplified if one formally assumes the brane charges and masses to be smeared over the whole internal manifold, which corresponds to taking into account their backreaction only in an averaged sense. I summarize recent progress in the understanding of the range of validity of this smearing approximation and comment on possible implications for attempts to build “classical” de Sitter vacua.
