When Worlds Collide

We study the neutral current flavour changing rare decay mode $B\\to X_s +$\nmissing energy within the framework of theories with large extra spatial\ndimensions. The corresponding Standard Model signature is $B\\to X_s + \\nu\n\\bar{\\nu}$. But in theories with large extra dimensions, it is possible to have\nscalars and gravitons in the final state making it quite distinct from any\nother scenario where there are no gravitons and the scalars are far too heavier\nthan the B-meson to be present as external particles. We give an estimate of\nthe branching ratio for such processes for different values of the number of\nextra dimensions and the effective scale of the effective theory.\n

In models of large extra dimensions, the fundamental Planck scale can be as low as TeV. Thus, in hadronic collisions interesting objects such as black holes, string balls, or p-branes can be produced. In scenarios of a fat brane or universal extra dimensions, the standard model particles are allowed to propagate in the extra spatial dimensions, which leads to the enhancement of the production cross sections of black holes and p-branes. Especially, the ratio of the p-brane cross section to the black hole cross section increases substantially, in comparison with the original confined scenario. The ratio can be as large as $105$ (for the case $n=7,m=5=p=r=k).$

A search is conducted for non-resonant new phenomena in dielectron and dimuon final states, originating from either contact interactions or large extra spatial dimensions. The LHC 2012 proton–proton collision dataset recorded by the ATLAS detector is used, corresponding to 20 fb^{-1} at sqrt{s} = 8 TeV. The dilepton invariant mass spectrum is a discriminating variable in both searches, with the contact interaction search additionally utilizing the dilepton forward-backward asymmetry. No significant deviations from the Standard Model expectation are observed. Lower limits are set on the ell ell q q contact interaction scale Lambda between 15.4 TeV and 26.3 TeV, at the 95 % credibility level. For large extra spatial dimensions, lower limits are set on the string scale M_mathrm{S} between 3.2 TeV to 5.0 TeV.

Solving the hierarchy problem without supersymmetry or extra dimensions: an alternative approach

Searches for extra spatial dimensions remain among the most popular new directions in our quest for physics beyond the Standard Model. High-energy collider experiments of the current decade should be able to find an ultimate answer to the question of their existence in a variety of models. We review these models and recent results from the Tevatron on searches for large, inverse-TeV-size, and Randall-Sundrum extra spatial dimensions. The most dramatic consequence of low-scale (~1 TeV) quantum gravity is copious production of mini-black holes at the LHC. We discuss selected topics in the mini-black-hole phenomenology.

The hierarchy problem can by addressed by extending the four-dimensional space-time to include an extra compact spatial dimension with non-trivial “warped” metric, as first suggested by Randall and Sundrum. If the Randall-Sundrum framework is realized in string theory, and if the Standard Model particles propagate in the extra dimension, Regge excitations of the Standard Model states should appear around the TeV scale. In a previous publication, we proposed a field-theoretic framework to model the tensor (spin-2) Regge partner of the gluon. Here, we use this framework to study the collider phenomenology of this particle. We find that Regge gluon decays involving Kaluza-Klein (KK) partners of Standard Model fields are very important. In particular, the decay to two KK gluons (with one possibly off-shell) dominates in most of the parameter space. This decay produces a very distinctive experimental signature: four highly boosted top quarks. We present a preliminary study of the detection prospects for this signal at the Large Hadron Collider (LHC). We find that Regge gluon masses up to about 2 TeV can be probed with 10 fb−1 of data at 7 TeV center-of-mass energy. With design luminosity at 14 TeV, the LHC should be sensitive to Regge gluon masses up to at least 3.5 TeV.

New Higgs signals from flavor physics in large extra dimensions

Grand unification at intermediate mass scales through extra dimensions

New instability for rotating black branes and strings

The DANSS detector is located near the power reactor at the Kalinin Nuclear Power Plant (at distances of 10.9–12.9 m) and is able to detect up to 5000 antineutrino events per day. The results of the search for Large Extra Dimensions in the simplest case of a single dominant large extra dimension are discussed. The particle oscillations to a finite-size extra dimension are assumed in this theory, and its predictions depend on the difference between the squared masses, as well as on the absolute scale of the neutrino masses. The sensitivity of the experiment to Large Extra Dimensions for various values of the model parameters such as the size of the large extra dimension a and the lightest-neutrino mass $${{m}_{0}}$$ can be determined by its Monte Carlo simulation. No statistically significant indications of the existence of Large Extra Dimensions have been obtained from the analysis of almost 5.8 million antineutrino events (the statistical confidence of the best point is only 2.0σ (1.8σ) for the normal (inverted) ordering of neutrino masses). The bounds have been determined for the size of the extra dimension and the lightest neutrino mass. These bounds for a number of regions are the best in the world. These bounds exclude a large fraction of the parameters preferable for explaining the gallium anomaly and the reactor antineutrino anomaly in this model, including the corresponding best points.

This dissertation presents the search for large extra dimensions using the rich and unique accelerator beam neutrino data collected by the MINOS and MINOS+ experiments from 2005 to 2012 and 2013 to 2016, respectively. Most data from neutrino oscillation experiments are consistent with the standard three-flavor paradigm. With increasing experimental precision, potential effects from physics beyond the Standard Model that could modify neutrino oscillations in subtle ways can be explored. One such scenario involves additional spatial dimensions. Following the Large Extra Dimensions (LED) model, sterile neutrinos arising as Kaluza-Klein states in an extra dimension with size R can mix with the three active neutrinos in 3+1 spacetime, thereby altering the neutrino oscillation probabilities. In addition, this model provides a natural explanation for small Dirac neutrino masses through mass suppression by the volume of the large extra dimensions. In this work, two analysis strategie s are employed to search for large extra dimensions: the Far-over-Near analysis and the two-detector analysis. In the former, the ratio of the neutrino energy spectra measured in the MINOS Far and Near Detectors is used to constrain the LED model parameters, while in the latter the measured spectra are used simultaneously. MINOS reported the strongest constraint on R from a neutrino oscillation experiment, constraining R to be smaller than $0.45\,\mu\text{m}$ at 90\% C.L. in the limit of a vanishing lightest neutrino mass, using the Far-over-Near approach. Including MINOS+ data, which significantly increases the number of events at higher neutrino energies away from the three-flavor minimum where the model effects are larger, and using the two-detector technique, the size of extra dimensions is further constrained to be smaller than $0.30\,\mu\text{m}$ at 90\% C.L. Stronger limits are obtained for non-vanishing lightest neutrino masses.

In presence of a magnetic field, photons can mix with any particle having a two-photon vertex. In theories with large compact extra-dimensions, there exists a hierachy of massive Kaluza-Klein gravitons that couple to any photon entering a magnetic field. We study this mixing and show that, in comparison with the four dimensional situation where the photon couples only to the massless graviton, the oscillation effect may be enhanced due to the existence of a large number of Kaluza-Klein modes. We give the conditions for such an enhancement and then investigate the cosmological and astrophysical consequences of this phenomenon; we also discuss some laboratory experiments. Axions also couple to photons in the same way; we discuss the effect of the existence of bulk axions in universes with large extra-dimensions. The results can also be applied to neutrino physics with extra-dimensions.

Motivated by a variety of theories that predict new effects, we tested the gravitational 1/r^2 law at separations between 10.77 mm and 137 microns using two different 10-fold azimuthally symmetric torsion pendulums and rotating 10-fold symmetric attractors. Our work improves upon other experiments by up to a factor of about 100. We found no deviation from Newtonian physics at the 95% confidence level and interpret these results as constraints on extensions of the Standard Model that predict Yukawa or power-law forces. We set a constraint on the largest single extra dimension (assuming toroidal compactification and that one extra dimension is significantly larger than all the others) of R <= 160 microns, and on two equal-sized large extra dimensions of R <= 130 microns. Yukawa interactions with |alpha| >= 1 are ruled out at 95% confidence for lambda >= 197 microns. Extra-dimensions scenarios stabilized by radions are restricted to unification masses M >= 3.0 TeV/c^2, regardless of the number of large extra dimensions. We also provide new constraints on power-law potentials V(r)\propto r^{-k} with k between 2 and 5 and on the gamma_5 couplings of pseudoscalars with m <= 10 meV/c^2.

We present limits for the compactification scale in the theory of Large Extra Dimensions (LED) proposed by Arkani-Hamed, Dimopoulos, and Dvali. We use 11 months of data from the Fermi Large Area Telescope (Fermi-LAT) to set gamma ray flux limits for 6 gamma-ray faint neutron stars (NS). To set limits on LED we use the model of Hannestad and Raffelt (HR) that calculates the Kaluza-Klein (KK) graviton production in supernova cores and the large fraction subsequently gravitationally bound around the resulting NS. The predicted decay of the bound KK gravitons to γγ should contribute to the flux from NSs. Considering 2 to 7 extra dimensions of the same size in the context of the HR model, we use Monte Carlo techniques to calculate the expected differential flux of gamma-rays arising from these KK gravitons, including the effects of the age of the NS, graviton orbit, and absorption of gamma-rays in the magnetosphere of the NS. We compare our Monte Carlo-based differential flux to the experimental differential flux using maximum likelihood techniques to obtain our limits on LED. Our limits are more restrictive than past EGRET-based optimistic limits that do not include these important corrections. Additionally, our limits are more stringent than LHC based limits for 3 or fewer LED, and comparable for 4 LED. We conclude that if the effective Planck scale is around a TeV, then for 2 or 3 LED the compactification topology must be more complicated than a torus.

Three flavour neutrino oscillations in models with large extra dimensions