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Landau Yang theorem is well known for the past several decades. It prohibits decay of a massive spin 1 particle to two photons. This emerges simply from the representation theory of the Poincare group and Bose Statistics. It does not require any action or Lagrangian. We generalize this theorem to theories with supersymmetry (SUSY) which disallows even decay to two photinos (Majorana fermions). We will prove that if the photon has a mass, howsoever small, this theorem can be evaded. We also show that the supersymmetric selection rule above can also be evaded through the Stueckelberg mass term. Further interesting implications are also pointed out., Comment: 17 pages

Noncommutative geometry is one of the quantum gravity theories, which various researchers have been using to describe different physical and astrophysical systems. However, so far, no direct observations can justify its existence, and this theory remains a hypothesis. On the other hand, over the past two decades, more than a dozen over-luminous type Ia supernovae have been observed, which indirectly predict that they originate from white dwarfs with super-Chandrasekhar masses $2.1-2.8 \rm\,M_\odot$. In this article, we discuss that considering white dwarfs as squashed fuzzy spheres, a class of noncommutative geometry, helps in accumulating more mass than the Chandrasekhar mass-limit. The length-scale beyond which the effect of noncommutativity becomes prominent is an emergent phenomenon, which depends only on the inter-electron separations in the white dwarf., Comment: 7 pages including 3 figures; based on the talk given in the parallel session "Quantum Gravity Phenomenology" in the Sixteenth Marcel Grossmann Meeting held online during July 5-10, 2021; to appear in the proceedings of Sixteenth Marcel Grossmann Meeting

We review gauge invariant $\mathcal N =1$ supersymmetric massive $U(1)$ gauge theory coupled to matter and Stuckelberg superfields. We focus on the leading order self energy and vertex correction to the matter field in the massless limit of both the $U(1)$ vector superfield and the Stuckelberg superfield. We explicitly verify that the theory is infrared divergence free in the massless limit. Hence the Stuckelberg mechanism appears to be the efficient route to handle infrared divergences seen in supersymmetric quantum electrodynamics.Since these additional particles have very small masses they can serve as dark matter candidates through `Ultralight particles' mechanism., Comment: 16 pages, 4 figures

In this letter, we propose a new model of fuzzy dark matter based on Stueckelberg theory. Dark matter is treated as a Bose-Einstein condensate of Stueckelberg particles and the resulting cosmological effects are analyzed. Fits are understood for the density and halo sizes of such particles and comparison with existing models is made. Certain attractive properties of the model are demonstrated and lines for future work are laid out., Comment: 11 pages, 4 figures, changes in presentation, additional references

Stueckelberg mechanism introduces a scalar field, known as Stueckelberg field, so that gauge symmetry is preserved in the massive abelian gauge theory. In this work, we show that the role of the Stueckelberg field is similar to the Kulish and Faddeev coherent state approach to handle infrared (IR) divergences. We expect that the light-front quantum electrodynamics (LFQED) with Stueckelberg field must be IR finite in the massless limit of the gauge boson. We have explicitly shown the cancellation of IR divergences in the relevant diagrams contributing to self-energy and vertex correction at leading order., Comment: 12 pages, 2 figures, references added

In a previous paper [1], we studied the $\eta'$ mass and formulated its chirally symmetric coupling to fermions which induces electric dipole moment (EDM). Here we calculate the EDM to one-loop. It is finite, having no ultraviolet divergence while its infrared divergence is canceled by soft photon emission processes \emph{exactly} as for $\theta=0$. The coupling does not lead to new divergences (not present for $\sin\theta=0$) in soft photon processes either. Furthermore, as it was argued previously [1], the EDM vanishes if suitable mixed quantum states are used. This means that in a quantum theory based on such mixed states, a strong bound on EDM will not necessarily lead to a strong bound such as $|\sin \theta|\lesssim 10^{-11}$ . This fact eliminates the need to fine-tune $\theta$ or for the axion field., Comment: 16 pages, 1 figure

The effective Lagrangian for \eta' incorporating the effect of the QCD \theta-angle has been developed previously. We revisit this Lagrangian and carry out its canonical quantization with particular attention to the test function spaces of constraints and the topology of the \eta'-field. In this way, we discover a new chirally symmetric coupling of this field to chiral multiplets which involves in particular fermions. This coupling violates P and T symmetries. In a subsequent paper, we will evaluate its contribution to the electric dipole moment (EDM) of fermions. Our motivation is to test whether the use of mixed states restores P and T invariance, so that EDM vanishes. This calculation will be shown to have striking new physical consequences., Comment: 14 pages, 1 figure; V2: NEW TITLE; revised version to be published in JHEP; references added

On Moyal space-time, one can implement twisted Poincar\'e symmetry with the resultant modification of symmetrization and anti-symmetrization postulates for bosons and fermions. We develop the thermofield approach of Umezawa and Takahashi on such a spacetime preserving the twisted Poincar\'e symmetry of the underlying quantum field theory(qft). Implications of this twisted Poincar\'e symmetry for qft's at finite temperature are pointed out., Comment: 11 pages, References added, Journal version

We analyse aspects of symmetry breaking for Moyal spacetimes within a quantisation scheme which preserves the twisted Poincar\'e symmetry. Towards this purpose, we develop the LSZ approach for Moyal spacetimes. The latter gives a formula for scattering amplitudes on these spacetimes which can be obtained from the corresponding ones on the commutative spacetime. This formula applies in the presence of spontaneous breakdown of symmetries as well.We also derive Goldstone's theorem on Moyal spacetime. The formalism developed here can be directly applied to the twisted standard model., Comment: +13 pages; minor changes in references,To appear in Phys Rev D

We study finite temperature phase transition of neutral scalar field on a fuzzy sphere using Monte Carlo simulations. We work with the zero mode in the temporal directions, while the effects of the higher modes are taken care by the temperature dependence of r. In the numerical calculations we use "pseudo-heatbath" method which reduces the auto-correlation considerably. Our results agree with the conventional calculations. We report some new results which show the presence of meta-stable states and also suggest that for suitable choice of parameters the symmetry breaking transition is of first order., Comment: 10 pages, 16 figures

We study noncommutative field theories, which are inherently nonlocal, using a Poincar\'e-invariant regularisation scheme which yields an effective, nonlocal theory for energies below a cut-off scale. After discussing the general features and the peculiar advantages of this regularisation scheme for theories defined in noncommutative spaces, we focus our attention onto the particular case when the noncommutativity parameter is inversely proportional to the square of the cut-off, via a dimensionless parameter $\eta$. We work out the perturbative corrections at one-loop order for a scalar theory with quartic interactions, where the signature of noncommutativity appears in $\eta$-dependent terms. The implications of this approach, which avoids the problems related to UV-IR mixing, are discussed from the perspective of the Wilson renormalisation program. Finally, we remark about the generality of the method, arguing that it may lead to phenomenologically relevant predictions, when applied to realistic field theories., Comment: 1+11 pages, 6 figures; v2: references added, typos corrected, conclusions unchanged