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We study 4D low-energy effective field theory, derived from heterotic string theory on the orbifolds. In particular, we study Abelian and non-Abelian discrete symmetries and their anomalies. Furthermore, stringy computations also provide with stringy coupling selection rules.
We investigate in detail the gravitational wave signal from kinks on cosmic (super)strings, including the kinematical effects from the internal extra dimensions. We find that the signal is suppressed, however, the effect is less significant that that for cusps. Combined with the greater incidence of kinks on (super)strings, it is likely that the kink signal offers the better chance for detection of cosmic (super)strings.
Cosmic super-strings interact generically with a tower of relatively light and/or strongly coupled Kaluza-Klein (KK) modes associated with the geometry of the internal space. In this paper, we study the production of spin-2 KK particles by cusps on loops of cosmic F- and D-strings. We consider cosmic super-strings localized either at the bottom of a warped throat or in a flat internal space with large volume. The total energy emitted by cusps in KK modes is comparable in both cases, although the number of produced KK modes may differ significantly. We then show that KK emission is constrained by the photo-dissociation of light elements and by observations of the diffuse gamma ray background. We show that this rules out regions of the parameter space of cosmic super-strings that are complementary to the regions that can be probed by current and upcoming gravitational wave experiments. KK modes are also expected to play an important role in the friction-dominated epoch of cosmic super-string evolution.
Space-filling S-branes can mediate a transition between a contracting and an expanding universe in the Einstein frame. Following up on previous work that uncovered such bouncing solutions in the context of weakly coupled thermal configurations of a certain class of type II superstrings, we set up here the formalism in which we can study the evolution of metric fluctuations across such an S-brane. Our work shows that the specific nature of the S-brane, which is sourced by non-trivial massless thermal string states and appears when the universe reaches a maximal critical temperature, allows for a scale invariant spectrum of curvature fluctuations to manifest at late times via a stringy realization of the matter bounce scenario. The finite energy density at the transition from contraction to expansion provides calculational control over the propagation of the curvature perturbations through the bounce, furnishing a working proof of concept that such a stringy universe can result in viable late time cosmology.
Multiloop superstring amplitudes are calculated within an extensively used gauge where the two-dimensional gravitino field carries Grassmann moduli. In general, the amplitudes possess, instead of modular symmetry, symmetry with respect to modular transformation supplemented with appropriate transformations of two-dimensional local supersymmetry. If the number of loops is larger than three, the integrationmeasures are notmodular forms, while the expression for the amplitude contains integrals along the boundary of the fundamental region of the modular group.
The Standard Model of particle physics treats quarks and leptons as having no size at all. Quarks are found inside protons and neutrons and the most familiar lepton is the electron. While the best measurements to date support that idea, there is circumstantial evidence that suggests that perhaps the these tiny particles might be composed of even smaller building blocks. This video explains this circumstantial evidence and introduces some very basic ideas of what those building blocks might be.
We consider the scattering amplitudes of five and six gravitons at tree level in superstring theory. Their power series expansions in the Regge slope {alpha}{sup '} are analyzed through the order {alpha}{sup '8} showing some interesting constraints on higher order gravitational couplings in the effective superstring action such as the absence of R{sup 5} terms. Furthermore, some transcendentality constraints on the coefficients of the nonvanishing couplings are observed: the absence of zeta values of even weight through the order {alpha}{sup '8} like the absence of {zeta}(2){zeta}(3)R{sup 6} terms. Our analysis is valid for any superstring background in any space-time dimension, which allows for a conformal field theory description.
We use the flat space limit of the AdS/CFT correspondence to derive a simple relation between the 2{yields}2 scattering amplitude of massless string states in type IIB superstring theory on ten-dimensional Minkowski space and a scaling limit of the N=4 super Yang-Mills four-point functions. We conjecture that this relation holds nonperturbatively and at arbitrarily high energy.
Superstring theory and other supersymmetric theories predict the existence of relatively light, weakly interacting scalar particles, called moduli, with a universal form of coupling to matter. Such particles can be emitted from cusps of cosmic strings, where extremely large Lorentz factors are achieved momentarily. Highly boosted modulus bursts emanating from cusps subsequently decay into gluons; they generate parton cascades which in turn produce large numbers of pions and then neutrinos. Because of very large Lorentz factors, extremely high energy neutrinos, up to the Planck scale and above, are produced. For some model parameters, the predicted flux of neutrinos with energies > or approx. 10{sup 21} eV is observable by JEM-EUSO and by the future large radio detectors LOFAR and SKA.
We analyze quartic gauge-invariant interactions of massless higher spin fields by using vertex operators constructed in our previous works and computing their 4-point amplitudes in superstring theory. The kinematic part of the quartic interactions of the higher spins is determined by the matter structure of their vertex operators; the nonlocality of the interactions is the consequence of the specific ghost structure of these operators. We compute explicitly the 4-point amplitude describing the complete gauge-invariant 1-1-3-3 quartic interaction (two massless spin 3 particles interacting with two photons) and comment on more general 1-1-s-s cases, particularly pointing out the structure of 1-1-5-5 coupling.
We study signatures of cosmic superstring networks containing strings of multiple tensions and Y junctions, on the cosmic microwave background (CMB) temperature and polarization spectra. Focusing on the crucial role of the string coupling constant g{sub s}, we show that the number density and energy density of the scaling network are dominated by different types of string in the g{sub s}{approx}1 and g{sub s}<<1 limits. This can lead to an observable shift in the position of the B-mode peak--a distinct signal leading to a direct constraint on g{sub s}. We forecast the joint bounds on g{sub s} and the fundamental string tension {mu}{sub F} from upcoming and future CMB polarization experiments, as well as the signal to noise in detecting the difference between B-mode signals in the limiting cases of large and small g{sub s}. We show that such a detectable shift is within reach of planned experiments.
In this paper it is studied a relation between the kappa-symmetric and pure spinor formulations of the supermembrane in eleven dimensions using Berkovits' recently developed method for the superstring (in D = 10). In the present paper I present an extension of this method to the supermembrane, showing that it is possible to reinstate the reparameterization constraints in the pure spinor formulation of the supermembrane by introducing a topological sector and performing a similarity transformation. The resulting BRST charge is then of conventional type and is argued to be (related to) the BRST charge of the kappa-symmetric supermembrane in a formulation where all second class constraints are 'gauge unfixed' to first class constraints. In the present analysis a natural candidate for a (non-covariant) supermembrane analogue of the superstring B-ghost is encountered.
We consider the perturbative stability of non-supersymmetric configurations in N=1 supergravity models with a spectator sector not involved in supersymmetry breaking. Motivated by the supergravity description of complex structure moduli in Large Volume Compactifications of type IIB-superstrings, we concentrate on models where the interactions are consistent with the supersymmetric truncation of the spectator fields, and we describe their couplings by a random ensemble of generic supergravity theories. We characterise the mass spectrum of the spectator fields in terms of the statistical parameters of the ensemble and the geometry of the scalar manifold. Our results show that the non-generic couplings between the spectator and the supersymmetry breaking sectors can stabilise all the tachyons which typically appear in the spectator sector before including the supersymmetry breaking effects, and we find large regions of the parameter space where the supersymmetric sector remains stable with probability close to one. We discuss these results about the stability of the supersymmetric sector in two physically relevant situations: non-supersymmetric Minkowski vacua, and slow-roll inflation driven by the supersymmetry breaking sector. For the class of models we consider, we have reproduced the regimes in which the KKLT and Large Volume Scenarios stabilise all supersymmetric moduli. We have also identified a new regime in which the supersymmetric sector is stabilised at a very robust type of dS minimum without invoking a large mass hierarchy.
We discuss how: (i) a dilaton/axion superfield can play the role of a Barbero-Immirzi field in four-dimensional conformal quantum supergravity theories, (ii) a fermionic component of such a dilaton/axion superfield may play the role of a Goldstino in the low-energy effective action obtained from a superstring theory with F-type global supersymmetry breaking, (iii) this global supersymmetry breaking is communicated to the gravitational sector via the supergravity coupling of the Goldstino, and (iv) such a scenario may be realized explicitly in a D-foam model with D-particle defects fluctuating stochastically.
A search for high-mass resonances decaying into tau-lepton pairs is performed using a data sample of pp collisions at $ \sqrt{s}=7 $ TeV. The data were collected with the CMS detector at the LHC and correspond to an integrated luminosity of 4.9 inverse femtobarns. The number of observed events is in agreement with the standard model prediction. An upper limit on the product of the resonance cross section and branching fraction into tau-lepton pairs is calculated as a function of the resonance mass. Using the sequential standard model resonance Z'(SSM) and the superstring-inspired E(6) model with resonance Z'(psi) as benchmarks, resonances with standard model couplings with masses below 1.4 and 1.1 TeV, respectively, are excluded at 95% confidence level.
We review the non-supersymmetric (Extended) Left-Right Symmetric Models (LRSM) and low energy E{sub 6}-based models to investigate if they can explain both the recently detected excess eejj signal at CMS and leptogenesis. The eejj excess can be explained from the decay of the right-handed gauge bosons (W{sub R}) with mass ∼ TeV in certain variants of the LRSM (with g{sub L}≠g{sub R}). However such scenarios can not accommodate high-scale leptogenesis. Other attempts have been made to explain leptogenesis while keeping the W{sub R} mass almost within the reach of the LHC by considering the resonant leptogenesis scenario in the context of the LRSM for relatively large Yukawa couplings. However, certain lepton number violating scattering processes involving the right-handed Higgs triplet and the right-handed neutrinos can stay in equilibrium till the electroweak phase transition and can washout the lepton asymmetry generated in the resonant leptogenesis scenario for mass range of W{sub R} as indicated by the CMS excess signal. Thus in such a scenario one needs to invoke post-sphaleron baryogenesis to explain the observed baryon asymmetry of the universe. Next, we consider three effective low energy subgroups of the superstring inspired E{sub 6} model having a number of additional exotic fermions which provides a rich phenomenology to be explored. We however find that these three effective low energy subgroups of E{sub 6} too cannot explain both the eejj excess signal and leptogenesis simultaneously.
In light of the present LHC Run II at √s = 13 TeV, a SM-like string model is studied. Specifically, a singlet S scalar-extended SM given in terms of four stacks of intersecting D6-branes in a type IIA superstring compactification producing a large gauge symmetry is examined. The scales involved are dealt with. According to the dark matter relic density, the mass of the scalar dark matter beyond the SM m{sub S} ≲ 10{sup 3} GeV and the corresponding Higgs portal couplings λ{sub SH} ≲ 10{sup –8} have been obtained.
A computer model which simulates, in principle, the chemical changes in the photooxidation of hydrocarbons using as input data a set of elementary reactions, corresponding kinetic rate data and appropriate initial conditions was developed. The Model was refined and exploited to examine more closely the photooxidation and photostabilization of a hydrocarbon polymer. The results lead to the following observations. (1) The time to failure, tau sub f (chosen as the level of 5% C-H bond oxidation which is within the range anticipated for marked change in mechanical properties) varies as the inverse square root of the light intensity. However, tau sub f is almost unaffected by both the photoinitiator type and concentration. (2) The time to failure decreases with the rate of abstraction of C-H by peroxy radicals but increases with the rate of bimolecular radical termination controlled by diffusion. (3) Of the various stabilization mechanisms considered, the trapping of peroxy radicals is distinctly the most effective, although the concommitant decomposition of hydroperoxide is also desirable.