共查询到20条相似文献,搜索用时 31 毫秒
1.
We introduce a new string-inspired approach to the subject of grand unification which allows the GUT scale to be small, ≲200 TeV,
so that it is within the reach of conceivable laboratory accelerated colliding beam devices. The key ingredient is a novel use of the heterotic string symmetry group physics
ideas to render baryon number violating effects small enough to have escaped detection to date. This part of the approach
involves new unknown parameters to be tested experimentally. A possible hint at the existence of these new parameters may
already exist in the EW precision data comparisons with the SM expectations. 相似文献
2.
《Nuclear Physics B》1995,457(3):409-483
We discuss the unification of gauge couplings within the framework of a wide class of realistic free-fermionic string models which have appeared in the literature, including the flipped SU(5), SO(6) × SO(4), and various SU(3) × SU(2) × U(1) models. If the matter spectrum below the string scale is that of the Minimal Supersymmetric Standard Model (MSSM), then string unification is in disagreement with experiment. We therefore examine several effects that may modify the minimal string predictions. First, we develop a systematic procedure for evaluating the one-loop heavy string threshold corrections in free-fermionic string models, and we explicitly evaluate these corrections for each of the realistic models. We find that these string threshold corrections are small, and we provide general arguments explaining why such threshold corrections are suppressed in string theory. Thus heavy thresholds cannot resolve the disagreement with experiment. We also study the effect of non-standard hypercharge normalizations, light SUSY thresholds, and intermediate-scale gauge structure, and similarly conclude that these effects cannot resolve the disagreement with low-energy data. Finally, we examine the effects of additional color triplets and electroweak doublets beyond the MSSM. Although not required in ordinary grand unification scenarios, such states generically appear within the context of certain realistic free-fermionic string models. We show that if these states exist at the appropriate thresholds, then the gauge couplings will indeed unify at the string scale. Thus, within these string models, string unification can be in agreement with low-energy data. 相似文献
3.
Mohab Abou-Zeid Christopher M. Hull Lionel J. Mason 《Communications in Mathematical Physics》2008,282(2):519-573
A family of new twistor string theories is constructed and shown to be free from world-sheet anomalies. The spectra in space-time
are calculated and shown to give Einstein supergravities with second order field equations instead of the higher derivative
conformal supergravities that arose from earlier twistor strings. The theories include one with the spectrum of N = 8 supergravity, another with the spectrum of N = 4 supergravity coupled to N = 4 super-Yang-Mills, and a family with N ≥ 0 supersymmetries with the spectra of self-dual supergravity coupled to self-dual super-Yang-Mills. The non-supersymmetric
string with N = 0 gives self-dual gravity coupled to self-dual Yang-Mills and a scalar. A three-graviton amplitude is calculated for the
N = 8 and N = 4 theories and shown to give a result consistent with the cubic interaction of Einstein supergravity. 相似文献
4.
Stefan Cordes Gregory Moore Sanjaye Ramgoolam 《Communications in Mathematical Physics》1997,185(3):543-619
We describe a topological string theory which reproduces many aspects of the 1/N expansion of SU(N) Yang-Mills theory in two spacetime dimensions in the zero coupling (A= 0) limit. The string theory is a modified version of topological gravity coupled to a topological sigma model with spacetime
as target. The derivation of the string theory relies on a new interpretation of Gross and Taylor's “Ω-1 points ”. We describe how inclusion of the area, coupling of chiral sectors, and Wilson loop expectation values can be incorporated
in the topological string approach.
Received: 3 March 1994 / Accepted: 2 February 1995 相似文献
5.
Sunil Mukhi 《Pramana》2000,54(4):543-559
In addition to being a prime candidate for a fundamental unified theory of all interactions in nature, string theory provides
a natural setting to understand gauge field theories. This is linked to the concept of ‘D-branes’: extended, solitonic excitations of string theory which can be studied using techniques of string theory and which
support gauge fields localized along their world-volumes. It follows that the techniques of string theory can be very useful
even for those particle physicists who are not specifically interested in unification and/or quantum gravity. In this talk
I attempt to review how strings help us to understand fields. The discussion is restricted to 3+1 spacetime dimensions. 相似文献
6.
7.
《Physics letters. [Part B]》1988,201(3):315-320
Minimal left-right (LR) models are often inconsistent with gauge unification at the Planck scale, as they imply too large a Weinberg angle. In (E6) superstring-inspired models true gauge unification is nit required, and the absence of unification of coupling constants might be an indication of non-zero (string) renormalization effects. Here we perform a quantitative analysis of the necessary spreading of the gauge coupling constants in order to accommodate a realistic value of the Weinberg angle in minimal LR models motivated by the string. 相似文献
8.
V. K. Oikonomou 《General Relativity and Gravitation》2012,44(5):1285-1297
We study massive spinor fields in the geometry of a straight cosmic string in a de Sitter background. We find a hidden N = 2 supersymmetry in the fermionic solutions of the equations of motion. We connect the zero mode solutions to the heat-kernel
regularized Witten index of the supersymmetric algebra. 相似文献
9.
Ignatios Antoniadis 《Pramana》2006,67(5):793-802
Type-I string theory in the presence of internal magnetic fields provides a concrete realization of split supersymmetry. To
lowest order, gauginos are massless while squarks and sleptons are superheavy. For weak magnetic fields, the correct Standard
Model spectrum guarantees gauge coupling unification with sin2
ϑW=3/8 at the compactification scale of M
GUT ⋍ 2 × 1016 GeV. I discuss mechanisms for generating gaugino and higgsino masses at the TeV scale, as well as generalizations to models
with split extended supersymmetry in the gauge sector. 相似文献
10.
V. D. Gershun 《Physics of Particles and Nuclei Letters》2011,8(3):293-298
We used the local invariant chiral currents to obtain new integrable string equations for string WZW model type with SU(3) constant torsion. We solved Burgers equation of motion for first invariant current in. terms of Lambert function. We show
that string model with SU(n), n > 3 constant torsion does not integrable, because procedure of decomposition of non-primitive invariant chiral currents to
primitive currents is the procedure of introduction of infinite-dimensions matrix of second kind constraints in bi-Hamiltonian
approach to integrable systems. 相似文献
11.
12.
We have constructed some Regge trajectories for mesons and baryons by taking the 70 MeV spinless mass quanta as the ultimate
building block for the light hadrons. In order to make masses integral multiples of seventy, small changes in masses has been
made with due explanation. We have shown how a linear relationship between J and M
2 is maintained by considering quantized hadron masses, which is a direct consequence of the string model and gives a strong
clue for quark confinement. It has also been established that mesons and baryons have different slopes and the slopes of baryons
is less than the slope of the mesons. This clearly defies the concept of universality of slopes (α ≈ 1.1 GeV2) of hadrons, which can only be achieved if the strings joining the quarks have constant string tension α = 1/(2πσ) (where σ is the string tension). 相似文献
13.
We discuss the main issues related to understanding closed string spectrum in Ramond-Ramond backgrounds on the example of AdS5 × S
5 and and its special limit – the maximally supersymmetric plane-wave background with constant null 5-form field strength. As we describe, in the latter case the spectrum can be found explicitly. We compare the plane-wave string spectrum with the expected form of the light-cone gauge spectrum of the AdS5 × S
5 superstring and comment on the tensionless string limit. 相似文献
14.
We discuss whether the (MSSM) unification of gauge couplings can be accommodated in string theories with a low (TeV) string scale. This requires either power law running of the couplings or logarithmic running extremely far above the string scale. In both cases it is difficult to arrange for the multiplet structure to give the MSSM result. For the case of power law running there is also enhanced sensitivity to the spectrum at the unification scale. For the case of logarithmic running there is a fine tuning problem associated with the light closed string Kaluza Klein spectrum which requires gauge mediated supersymmetry breaking on the “visible” brane with a dangerously low scale of supersymmetry breaking. Evading these problems in low string scale models requires a departure from the MSSM structure, which would imply that the success of gauge unification in the MSSM is just an accident. 相似文献
15.
The partition function of an N=2{\mathcal {N}=2} gauge theory in the Ω-background satisfies, for generic value of the parameter b = -e1/e2{\beta=-{\epsilon_1}/{\epsilon_2}} , the, in general extended, but otherwise β-independent, holomorphic anomaly equation of special geometry. Modularity together with the (β-dependent) gap structure at the various singular loci in the moduli space completely fixes the holomorphic ambiguity, also
when the extension is non-trivial. In some cases, the theory at the orbifold radius, corresponding to β = 2, can be identified with an “orientifold” of the theory at β = 1. The various connections give hints for embedding the structure into the topological string. 相似文献
16.
M. Hamani Daouda Manuel E. Rodrigues M. J. S. Houndjo 《The European Physical Journal C - Particles and Fields》2012,72(2):1893
We develop the reconstruction of the f(T) gravity model according to the holographic dark energy. T is the torsion scalar and its initial value from the teleparallel gravity is imposed for fitting the initial value of the
function f(T). The evolutionary nature of the holographic dark energy is essentially based on two important parameters, Ω
V
and ω
V
, respectively, the dimensionless dark energy and the parameter of the equation of state, related to the holographic dark
energy. The result shows a polynomial function for f(T), and we also observe that, when Ω
V
→1 at the future time, ω
V
may cross −1 for some values of the input parameter b. Another interesting aspect of the obtained model is that it provides a unification scenario of dark matter with dark energy. 相似文献
17.
18.
It is shown that homogeneous plane symmetric string cosmological model for Takabayasi string i.e. ρ=(1+ω)λ does not exist in Barber’s second self creation theory. Further it is found that the string cosmological model in this theory
exist only when ω=0. Therefore model for ρ=λ (geometric string) is constructed. Some physical and geometrical properties of the model are discussed. 相似文献
19.
《Nuclear Physics B》1988,307(1):145-156
Like grand unification of old, string unification predicts simple tree-level relations between the couplings of all unbroken gauge groups such as SU(3)C or SU(2)W. I show here how to compute one-loop corrections to these relations for any four-dimensional model based on a classical vacuum of the heterotic string. The result can be used to calculate both sin2θWand ΛQCD in terms of αQCD and MPlanck. 相似文献
20.
A. Sheykhi K. Karami M. Jamil E. Kazemi M. Haddad 《General Relativity and Gravitation》2012,44(3):623-638
In the derivation of holographic dark energy density, the area law of the black hole entropy plays a crucial role. However,
the entropy-area relation can be modified from the inclusion of quantum effects, motivated from the loop quantum gravity,
string theory and black hole physics. In this paper, we study cosmological implication of the interacting entropy-corrected
holographic dark energy model in the framework of Brans–Dicke cosmology. We obtain the equation of state and the deceleration
parameters of the entropy-corrected holographic dark energy in a non-flat Universe. As system’s IR cutoff we choose the radius
of the event horizon measured on the sphere of the horizon, defined as L = ar(t). We find out that when the entropy-corrected holographic dark energy is combined with the Brans–Dicke field, the transition
from normal state where w
D
> −1 to the phantom regime where w
D
< −1 for the equation of state of interacting dark energy can be more easily achieved for than when resort to the Einstein
field equations is made. 相似文献